1 00:00:00,601 --> 00:00:02,901 ♪ ♪ 2 00:00:02,903 --> 00:00:05,504 JANNNNA LEVIN: Of all the objects in the cosmos... 3 00:00:05,506 --> 00:00:06,739 Planets... 4 00:00:06,741 --> 00:00:08,140 Stars... 5 00:00:08,142 --> 00:00:10,275 Galaxies... 6 00:00:10,277 --> 00:00:11,543 (explosion echoes) 7 00:00:11,545 --> 00:00:13,412 LEVIN: None are as strange, 8 00:00:13,414 --> 00:00:15,414 mysterious, 9 00:00:15,416 --> 00:00:16,448 or powerful 10 00:00:16,450 --> 00:00:18,784 as black holes. 11 00:00:18,786 --> 00:00:20,719 ♪ ♪ 12 00:00:20,721 --> 00:00:22,121 NEIL DEGRASSE TYSON: Black holes are 13 00:00:22,123 --> 00:00:25,391 the most mind-blowing things in the universe. 14 00:00:25,393 --> 00:00:26,725 PRIYAMVADA NATARAJAN: They can swallow a star 15 00:00:26,727 --> 00:00:28,360 completely intact. 16 00:00:29,930 --> 00:00:32,998 FERYAL OZEL: Black holes have these powerful jets 17 00:00:33,000 --> 00:00:34,166 that just spew matter out. 18 00:00:34,168 --> 00:00:36,635 LEVIN: First discovered on paper... 19 00:00:36,637 --> 00:00:38,871 PETER GALISON On the back of an envelope, 20 00:00:38,873 --> 00:00:40,439 some squiggles of the pen. 21 00:00:40,441 --> 00:00:42,908 LEVIN: ...the bizarre solution 22 00:00:42,910 --> 00:00:46,578 to a seemingly unsolvable equation... 23 00:00:46,580 --> 00:00:47,413 A mathematical enigma... 24 00:00:47,415 --> 00:00:49,448 LEVIN: Einstein himself 25 00:00:49,450 --> 00:00:52,051 could not accept black holes as real. 26 00:00:52,053 --> 00:00:53,952 People didn't even believe for many years that they existed. 27 00:00:53,954 --> 00:00:55,888 Nature doesn't work that way. 28 00:00:55,890 --> 00:00:58,590 ♪ ♪ 29 00:00:58,592 --> 00:01:03,228 LEVIN: Yet slowly, as scientists investigate black holes 30 00:01:03,230 --> 00:01:04,663 by observing the effect they have 31 00:01:04,665 --> 00:01:06,298 on their surroundings, 32 00:01:06,300 --> 00:01:08,967 evidence begins to mount... 33 00:01:08,969 --> 00:01:10,903 ANDREA GHEZ: That is the proof of a black hole. 34 00:01:10,905 --> 00:01:14,239 TYSON: Millions of times the mass of the sun. 35 00:01:14,241 --> 00:01:17,943 LEVIN: Cutting-edge discoveries show... 36 00:01:17,945 --> 00:01:18,510 We did it! 37 00:01:18,512 --> 00:01:19,645 (applause) 38 00:01:19,647 --> 00:01:22,881 LEVIN: ...black holes are very real. 39 00:01:22,883 --> 00:01:24,850 I thought it was crazy. 40 00:01:24,852 --> 00:01:26,418 I said, "Holy (bleep)!" 41 00:01:26,420 --> 00:01:30,889 ♪ ♪ 42 00:01:30,891 --> 00:01:32,958 LEVIN: But what exactly are they? 43 00:01:32,960 --> 00:01:37,896 If we could visit one, what might we see? 44 00:01:37,898 --> 00:01:42,201 With their immense power, do black holes somehow shape 45 00:01:42,203 --> 00:01:44,470 the very structure of the universe? 46 00:01:44,472 --> 00:01:48,841 Is it possible we might not exist without them? 47 00:01:50,211 --> 00:01:51,310 It's quite a journey. 48 00:01:51,312 --> 00:01:54,012 ♪ ♪ 49 00:01:54,014 --> 00:01:55,714 LEVIN: "Black Hole Apocalypse." 50 00:01:55,716 --> 00:01:59,418 Right now on "NOVA." 51 00:01:59,420 --> 00:02:02,955 ♪ ♪ 52 00:02:06,493 --> 00:02:10,495 VIN: There are apocalyptic objects in the universe: 53 00:02:10,497 --> 00:02:12,997 engines of destruction, 54 00:02:12,999 --> 00:02:17,602 menacing and mysterious. 55 00:02:17,604 --> 00:02:19,404 Black holes. 56 00:02:20,574 --> 00:02:23,074 Even scientists who study them 57 00:02:23,076 --> 00:02:25,210 find them astonishing. 58 00:02:25,212 --> 00:02:29,280 EILAT GLIKMAN: Black holes can sort of blow your mind. 59 00:02:29,282 --> 00:02:32,083 I'm amazed that these objects actually exist. 60 00:02:33,620 --> 00:02:38,523 LEVIN: Black holes defy our understanding of nature. 61 00:02:38,525 --> 00:02:40,191 Black holes are the greatest mystery in the universe. 62 00:02:40,193 --> 00:02:43,194 LEVIN: They're completely invisible, 63 00:02:43,196 --> 00:02:45,964 yet powerful beyond imagining. 64 00:02:45,966 --> 00:02:49,734 They can tear a star to shreds. 65 00:02:49,736 --> 00:02:51,870 OZEL: Black holes actually 66 00:02:51,872 --> 00:02:54,239 will eat anything that comes in their path. 67 00:02:55,909 --> 00:02:57,942 You really want to avoid them at all cost. 68 00:02:57,944 --> 00:03:02,347 LEVIN: Black holes even slow time. 69 00:03:02,349 --> 00:03:05,116 Once thought too strange to be real... 70 00:03:05,118 --> 00:03:06,551 (glass shatters) 71 00:03:06,553 --> 00:03:10,722 ...black holes shatter our very understanding of physics. 72 00:03:10,724 --> 00:03:13,291 But we're learning they may somehow be necessary 73 00:03:13,293 --> 00:03:16,294 for the universe we know to exist. 74 00:03:16,296 --> 00:03:19,397 They might well be the key players in the universe. 75 00:03:19,399 --> 00:03:24,202 LEVIN: What are these strange, powerful objects, 76 00:03:24,204 --> 00:03:27,539 outrageous and surprising? 77 00:03:27,541 --> 00:03:32,210 Where are they, and how do they control the universe? 78 00:03:32,212 --> 00:03:34,646 The search for black holes is on. 79 00:03:34,648 --> 00:03:39,217 And it will be a wild ride across the cosmos 80 00:03:39,219 --> 00:03:43,288 to places where everything you think you know is challenged -- 81 00:03:43,290 --> 00:03:46,624 where space and time, even reality, 82 00:03:46,626 --> 00:03:48,526 are stranger than fiction. 83 00:03:48,528 --> 00:03:51,696 ♪ ♪ 84 00:03:55,869 --> 00:04:01,439 And we're starting that journey at a very unlikely place: 85 00:04:01,441 --> 00:04:06,311 here, at a remote location in Washington state, 86 00:04:06,313 --> 00:04:08,546 where-- for the first time-- 87 00:04:08,548 --> 00:04:13,451 a radical new experiment has detected black holes. 88 00:04:13,453 --> 00:04:17,222 It originated over 50 years ago, 89 00:04:17,224 --> 00:04:21,359 when a few visionary scientists 90 00:04:21,361 --> 00:04:24,596 imagine a technology that hasn't yet been invented... 91 00:04:24,598 --> 00:04:27,131 ♪ ♪ 92 00:04:27,133 --> 00:04:31,769 Searching for something no one is certain can be found. 93 00:04:31,771 --> 00:04:34,572 The experiment is daring and risky. 94 00:04:34,574 --> 00:04:39,277 Failure could mark their lives forever. 95 00:04:39,279 --> 00:04:40,845 But they don't fail. 96 00:04:40,847 --> 00:04:42,680 Right here, in these facilities, 97 00:04:42,682 --> 00:04:44,883 they make a remarkable discovery. 98 00:04:47,621 --> 00:04:51,589 In the early hours of September 14, 2015, 99 00:04:51,591 --> 00:04:53,658 they record a message. 100 00:04:53,660 --> 00:04:58,229 It looks and sounds like this. 101 00:04:58,231 --> 00:04:59,831 (chirp) 102 00:04:59,833 --> 00:05:01,533 Just a little chirp. 103 00:05:01,535 --> 00:05:06,404 But that chirp is epic, monumental. 104 00:05:06,406 --> 00:05:10,742 The signal traveled over a billion light years to reach us. 105 00:05:10,744 --> 00:05:14,612 ♪ ♪ 106 00:05:14,614 --> 00:05:17,315 It started far, far away. 107 00:05:17,317 --> 00:05:20,518 And what it tells us is this: 108 00:05:20,520 --> 00:05:24,989 somewhere in the cosmos, over a billion years ago, 109 00:05:24,991 --> 00:05:32,196 two massive black holes circle each other in a fatal encounter. 110 00:05:32,198 --> 00:05:34,232 Closer and closer they come, 111 00:05:34,234 --> 00:05:36,901 swirling faster and faster, 112 00:05:36,903 --> 00:05:39,804 until finally, they slam together. 113 00:05:39,806 --> 00:05:41,306 (drum beats) 114 00:05:41,308 --> 00:05:44,509 The black holes create waves that spread outward. 115 00:05:44,511 --> 00:05:46,110 (drum beats) 116 00:05:46,112 --> 00:05:47,612 Just like vibrations on a drum, 117 00:05:47,614 --> 00:05:53,418 a ringing in the fabric of space itself. 118 00:05:53,420 --> 00:05:57,155 The collision creates a massive blast, 119 00:05:57,157 --> 00:05:59,157 putting out 50 times as much power 120 00:05:59,159 --> 00:06:03,695 as the entire visible universe. 121 00:06:03,697 --> 00:06:07,966 It sends out a wave not of heat, or light, or sound, 122 00:06:07,968 --> 00:06:11,202 but of gravity. 123 00:06:11,204 --> 00:06:13,271 This gravity wave is moving its way through the universe 124 00:06:13,273 --> 00:06:15,073 at the speed of light. 125 00:06:15,075 --> 00:06:17,308 ♪ ♪ 126 00:06:17,310 --> 00:06:19,811 LEVIN: The wave races by stars. 127 00:06:19,813 --> 00:06:23,615 On the young Earth, supercontinents are forming. 128 00:06:23,617 --> 00:06:27,852 Microscopic organisms have just appeared. 129 00:06:27,854 --> 00:06:29,220 TYSON: Washing over one galaxy 130 00:06:29,222 --> 00:06:31,155 after another, after another. 131 00:06:32,559 --> 00:06:36,094 LEVIN: Dinosaurs roam the Earth. 132 00:06:36,096 --> 00:06:37,195 The wave is still moving. 133 00:06:37,197 --> 00:06:41,633 LEVIN: It zooms through clouds of dust. 134 00:06:41,635 --> 00:06:43,801 And then it nears the Milky Way Galaxy. 135 00:06:43,803 --> 00:06:47,305 LEVIN: The Ice Age is just beginning. 136 00:06:47,307 --> 00:06:51,509 We're troglodytes, drawing in caves. 137 00:06:51,511 --> 00:06:55,313 LEVIN: The wave reaches nearby stars. 138 00:06:55,315 --> 00:06:58,883 Albert Einstein is in the sixth grade. 139 00:06:58,885 --> 00:07:03,021 The wave approaches as close as Alpha Centauri. 140 00:07:03,023 --> 00:07:07,392 At midnight on September 13, 2015, 141 00:07:07,394 --> 00:07:09,894 it is as close as Saturn. 142 00:07:09,896 --> 00:07:14,132 Finally, over a billion years after the black holes collide, 143 00:07:14,134 --> 00:07:16,034 the wave reaches us. 144 00:07:16,036 --> 00:07:17,535 It strikes a pair 145 00:07:17,537 --> 00:07:20,438 of revolutionary new observatories-- 146 00:07:20,440 --> 00:07:24,809 the sites of the daring experiment. 147 00:07:26,179 --> 00:07:27,345 (faint chirp) 148 00:07:31,017 --> 00:07:32,817 This is LIGO, 149 00:07:32,819 --> 00:07:37,422 the Laser Interferometer Gravitational Wave Observatory. 150 00:07:37,424 --> 00:07:40,058 The experiment 50 years in the making 151 00:07:40,060 --> 00:07:42,960 has finally hit the jackpot-- 152 00:07:42,962 --> 00:07:47,465 and opened an entirely new way of exploring the universe. 153 00:07:47,467 --> 00:07:53,037 For 400 years, almost everything we've observed in space 154 00:07:53,039 --> 00:07:58,409 has come to us in some form of electromagnetic energy. 155 00:07:58,411 --> 00:08:00,611 (chirp) 156 00:08:00,613 --> 00:08:02,947 That little chirp is different. 157 00:08:02,949 --> 00:08:06,551 What hits the Earth in September 2015 158 00:08:06,553 --> 00:08:09,120 is a gravitational wave-- 159 00:08:09,122 --> 00:08:13,858 a squeezing and stretching of the very fabric of space. 160 00:08:13,860 --> 00:08:16,761 It produced no light; 161 00:08:16,763 --> 00:08:21,265 no telescope could ever see the collision. 162 00:08:21,267 --> 00:08:27,805 We needed an entirely new kind of observatory to detect it. 163 00:08:27,807 --> 00:08:30,241 That wave is new and direct evidence 164 00:08:30,243 --> 00:08:33,377 of one of the strangest mysteries in our universe: 165 00:08:33,379 --> 00:08:34,378 black holes. 166 00:08:34,380 --> 00:08:36,647 ♪ ♪ 167 00:08:36,649 --> 00:08:39,350 Most of us have heard of black holes. 168 00:08:39,352 --> 00:08:41,919 They're invisible, powerful... 169 00:08:41,921 --> 00:08:43,221 NATARAJAN: We are talking about things 170 00:08:43,223 --> 00:08:45,656 that are a billion times the mass of the sun. 171 00:08:45,658 --> 00:08:48,259 LEVIN: Bizarre. 172 00:08:48,261 --> 00:08:50,061 GLIKMAN: A physical entity 173 00:08:50,063 --> 00:08:52,964 with infinite density. 174 00:08:52,966 --> 00:08:54,766 No beginning, no end. 175 00:08:54,768 --> 00:08:56,901 LEVIN: They pull things in. 176 00:08:58,338 --> 00:09:01,706 And warp light. 177 00:09:01,708 --> 00:09:06,711 Approach one, and time itself begins to change. 178 00:09:06,713 --> 00:09:11,215 NATARAJAN: The gravity is so intense that a moving clock 179 00:09:11,217 --> 00:09:12,517 will tick slower. 180 00:09:12,519 --> 00:09:16,654 TYSON: Time will become so slow for you 181 00:09:16,656 --> 00:09:21,726 that you will watch the entire future of the universe 182 00:09:21,728 --> 00:09:23,795 unfold before your very eyes. 183 00:09:26,599 --> 00:09:32,303 LEVIN: Fall in, and you'd be squeezed as thin as a noodle. 184 00:09:32,305 --> 00:09:36,207 TYSON: You'll be extruded through the fabric of space and time 185 00:09:36,209 --> 00:09:38,643 like toothpaste through a tube. 186 00:09:38,645 --> 00:09:42,513 ♪ ♪ 187 00:09:42,515 --> 00:09:47,051 LEVIN: Today, we know more about black holes than ever before. 188 00:09:47,053 --> 00:09:52,924 But the more we learn, the more mysterious they become. 189 00:09:52,926 --> 00:09:55,626 GHEZ: They're the most exotic objects in the universe. 190 00:09:55,628 --> 00:09:57,361 We don't have the physics to describe them. 191 00:09:57,363 --> 00:09:59,597 NATARAJAN: No matter how well you understand them, 192 00:09:59,599 --> 00:10:01,999 they remain unreachable in some sense. 193 00:10:02,001 --> 00:10:08,039 ANNOUNCER (on film): Now man is about to enter... 194 00:10:08,041 --> 00:10:09,941 the black hole! 195 00:10:09,943 --> 00:10:11,843 (machine beeping) 196 00:10:14,214 --> 00:10:16,614 So black holes have a pretty fierce reputation. 197 00:10:16,616 --> 00:10:20,885 And if you want a villain for a sci-fi movie, cast a black hole. 198 00:10:20,887 --> 00:10:24,822 But in reality, what exactly is a black hole? 199 00:10:24,824 --> 00:10:26,557 And where do they come from? 200 00:10:26,559 --> 00:10:31,562 You might think a black hole is like this-- an object. 201 00:10:31,564 --> 00:10:32,864 But it's not. 202 00:10:32,866 --> 00:10:38,169 It's a hole in the fabric of space. 203 00:10:38,171 --> 00:10:41,305 A place where there is nothing; nothing except gravity, 204 00:10:41,307 --> 00:10:44,642 gravity at its most intense and overwhelming. 205 00:10:44,644 --> 00:10:48,479 ♪ ♪ 206 00:10:48,481 --> 00:10:51,449 So if black holes are all about gravity-- 207 00:10:51,451 --> 00:10:54,518 gravity at its most extreme-- 208 00:10:54,520 --> 00:10:57,255 what exactly is gravity? 209 00:10:57,257 --> 00:11:02,026 ♪ ♪ 210 00:11:02,028 --> 00:11:03,461 (bell rings) 211 00:11:03,463 --> 00:11:06,530 (people chatting) 212 00:11:06,532 --> 00:11:09,267 We're all familiar with gravity. 213 00:11:09,269 --> 00:11:11,569 (plates crash): Yep, it's Friday. 214 00:11:13,006 --> 00:11:14,572 LEVIN: It rules our lives. 215 00:11:14,574 --> 00:11:18,209 But even so, for a very long time, 216 00:11:18,211 --> 00:11:20,378 how gravity actually works 217 00:11:20,380 --> 00:11:23,447 was one of the greatest mysteries. 218 00:11:23,449 --> 00:11:26,050 Over 300 years ago, 219 00:11:26,052 --> 00:11:28,152 Isaac Newton was fascinated 220 00:11:28,154 --> 00:11:30,154 with the behavior of moving objects. 221 00:11:30,156 --> 00:11:35,459 Eventually he figured out his laws of motion. 222 00:11:35,461 --> 00:11:38,195 They work so well, we still use them today. 223 00:11:38,197 --> 00:11:41,165 MAN (on film): Lift-off, we have lift-off at 9:34 a.m. 224 00:11:41,167 --> 00:11:45,102 But Newton's laws can only describe gravity's effects, 225 00:11:45,104 --> 00:11:47,738 not explain what it is. 226 00:11:47,740 --> 00:11:49,941 NEWTON (dramatized): Hm. 227 00:11:49,943 --> 00:11:51,776 And here's where Albert Einstein comes in. 228 00:11:51,778 --> 00:11:53,511 (camera clicking) 229 00:11:53,513 --> 00:11:56,213 Like Newton, he thinks about objects in motion. 230 00:11:56,215 --> 00:12:01,519 And he wonders what gravity actually is. 231 00:12:01,521 --> 00:12:03,888 Is it a force? 232 00:12:03,890 --> 00:12:05,856 Or could it be something else? 233 00:12:08,695 --> 00:12:10,494 Here's what concerns Einstein. 234 00:12:10,496 --> 00:12:13,364 Take this apple. 235 00:12:13,366 --> 00:12:18,302 I can't move it without touching it. 236 00:12:18,304 --> 00:12:22,440 But if I drop the apple, it moves toward the Earth. 237 00:12:22,442 --> 00:12:24,742 But what if I take my hand away, 238 00:12:24,744 --> 00:12:27,845 and the floor, and the basement, and the floor below that? 239 00:12:27,847 --> 00:12:29,447 Then what happens? 240 00:12:31,084 --> 00:12:34,952 The apple just keeps falling. 241 00:12:34,954 --> 00:12:38,756 Einstein realized that gravity 242 00:12:38,758 --> 00:12:41,459 had something to do with falling. 243 00:12:43,463 --> 00:12:47,798 Now, if I throw the apple, 244 00:12:47,800 --> 00:12:51,736 it falls along a curved path. 245 00:12:51,738 --> 00:12:56,273 But imagine I could get the apple moving much faster. 246 00:12:56,275 --> 00:13:00,277 (cannon firing) 247 00:13:00,279 --> 00:13:03,047 Eventually, if I get the apple moving really, really fast-- 248 00:13:03,049 --> 00:13:05,883 say, 17,000 miles an hour-- 249 00:13:05,885 --> 00:13:10,855 its curved path matches the curve of the Earth. 250 00:13:10,857 --> 00:13:13,924 The apple is in orbit, falling freely, 251 00:13:13,926 --> 00:13:17,361 just like the International Space Station 252 00:13:17,363 --> 00:13:19,864 and the astronauts inside it. 253 00:13:19,866 --> 00:13:23,134 According to Einstein, the apple-- 254 00:13:23,136 --> 00:13:25,770 and the space station, and the astronauts-- 255 00:13:25,772 --> 00:13:32,109 are all falling freely along a curved path in space. 256 00:13:32,111 --> 00:13:34,278 And what makes that path curved? 257 00:13:34,280 --> 00:13:36,013 The mass of the Earth. 258 00:13:36,015 --> 00:13:41,052 GALISON: Einstein came up with a supremely simple concept, 259 00:13:41,054 --> 00:13:44,155 and that is that space and time is bent by the Earth, 260 00:13:44,157 --> 00:13:46,157 and by the sun, and by all the objects in the world. 261 00:13:46,159 --> 00:13:48,726 So according to Einstein, 262 00:13:48,728 --> 00:13:57,201 the mass of every object causes the space around it to curve. 263 00:13:57,203 --> 00:13:59,303 GALISON: And that was Einstein's conception. 264 00:13:59,305 --> 00:14:01,605 There are no forces anymore. 265 00:14:01,607 --> 00:14:04,408 There's just objects bending space-time 266 00:14:04,410 --> 00:14:08,612 and other objects following the straightest line through it. 267 00:14:08,614 --> 00:14:15,186 LEVIN: All objects in motion follow the curves in space. 268 00:14:15,188 --> 00:14:20,157 So how does the Earth move the apple without touching it? 269 00:14:20,159 --> 00:14:22,193 The Earth curves space, 270 00:14:22,195 --> 00:14:26,764 and the apple falls freely along those curves. 271 00:14:26,766 --> 00:14:29,700 That, according to Einstein's general theory of relativity, 272 00:14:29,702 --> 00:14:32,336 is gravity: curved space. 273 00:14:32,338 --> 00:14:35,206 And that understanding of gravity-- 274 00:14:35,208 --> 00:14:38,642 that an object causes the space around it to curve-- 275 00:14:38,644 --> 00:14:43,547 leads directly to black holes. 276 00:14:43,549 --> 00:14:46,817 But it's not Albert Einstein who first makes the connection 277 00:14:46,819 --> 00:14:50,054 between gravity and black holes. 278 00:14:50,056 --> 00:14:52,790 It's another scientist. 279 00:14:52,792 --> 00:14:54,291 MARCIA BARTUSIAK: Karl Schwarzschild 280 00:14:54,293 --> 00:14:56,360 was a German astronomer, 281 00:14:56,362 --> 00:14:59,029 head of the Potsdam Observatory in Germany. 282 00:14:59,031 --> 00:15:03,000 Ever since he was a teenager, he had been calculating 283 00:15:03,002 --> 00:15:05,202 complicated features of planetary orbits. 284 00:15:06,873 --> 00:15:11,208 LEVIN: As Einstein unveils his theory of gravity in 1915, 285 00:15:11,210 --> 00:15:15,112 Karl Schwarzschild is in the German army, 286 00:15:15,114 --> 00:15:20,084 calculating artillery trajectories in World War I. 287 00:15:20,086 --> 00:15:24,255 BARTUSIAK: And just weeks after Einstein presented his papers, 288 00:15:24,257 --> 00:15:27,658 Schwarzschild, then on the Russian front, 289 00:15:27,660 --> 00:15:31,896 quickly got a copy and was mapping 290 00:15:31,898 --> 00:15:36,200 the gravitational field around a star. 291 00:15:36,202 --> 00:15:37,434 GALISON: Einstein had gotten at it 292 00:15:37,436 --> 00:15:39,570 through a series of approximations. 293 00:15:39,572 --> 00:15:43,307 But Schwarzschild, sitting on the front 294 00:15:43,309 --> 00:15:45,142 with bullets and bombs flying, 295 00:15:45,144 --> 00:15:49,346 calculated an exact solution to Einstein's theory 296 00:15:49,348 --> 00:15:54,485 and sent it to Einstein. 297 00:15:54,487 --> 00:15:56,987 Einstein was astonished. 298 00:15:56,989 --> 00:15:58,189 He hadn't even imagined 299 00:15:58,191 --> 00:15:59,890 that you could solve these equations exactly. 300 00:15:59,892 --> 00:16:04,094 LEVIN: But Schwarzschild isn't done. 301 00:16:04,096 --> 00:16:06,697 In his solution to Einstein's equations, 302 00:16:06,699 --> 00:16:12,736 he discovers something Einstein himself had not anticipated. 303 00:16:12,738 --> 00:16:14,271 GALISON: Schwarzschild said, 304 00:16:14,273 --> 00:16:18,175 "I can calculate this strange distance 305 00:16:18,177 --> 00:16:19,643 "from a gravitating object 306 00:16:19,645 --> 00:16:23,547 that represents a kind of boundary." 307 00:16:23,549 --> 00:16:27,918 LEVIN: Schwarzschild mathematically concentrates a mass-- 308 00:16:27,920 --> 00:16:29,453 for example, a star-- 309 00:16:29,455 --> 00:16:34,058 into a single point. 310 00:16:34,060 --> 00:16:37,628 Then he calculates how that mass would bend space 311 00:16:37,630 --> 00:16:41,999 and curve rays of light passing nearby. 312 00:16:42,001 --> 00:16:44,368 BARTUSIAK: As he, through his mathematics, 313 00:16:44,370 --> 00:16:48,906 aimed particles of light or matter towards this point, 314 00:16:48,908 --> 00:16:53,043 there was this boundary surrounding the point 315 00:16:53,045 --> 00:16:56,080 at which the particles would just stop. 316 00:16:58,317 --> 00:17:00,584 The particles disappeared. 317 00:17:00,586 --> 00:17:01,819 Time stopped. 318 00:17:01,821 --> 00:17:04,922 LEVIN: Schwarzschild has discovered 319 00:17:04,924 --> 00:17:07,858 that a concentration of mass will warp space 320 00:17:07,860 --> 00:17:09,526 to such an extreme 321 00:17:09,528 --> 00:17:13,297 that it creates a region of no return. 322 00:17:13,299 --> 00:17:16,066 Anything that enters that region will be trapped, 323 00:17:16,068 --> 00:17:20,204 unable to escape-- even light. 324 00:17:20,206 --> 00:17:21,672 GALISON: It's like those roach motels. 325 00:17:21,674 --> 00:17:23,841 You can check in, but you can't check out. 326 00:17:23,843 --> 00:17:25,776 Once you go across that boundary, 327 00:17:25,778 --> 00:17:28,112 even if you can sail through, 328 00:17:28,114 --> 00:17:30,080 there's nothing you can do to get out, 329 00:17:30,082 --> 00:17:31,982 there's nothing you can do to signal out. 330 00:17:31,984 --> 00:17:36,287 It becomes this strange, cut-off portion of space-time. 331 00:17:36,289 --> 00:17:41,592 LEVIN: What Karl Schwarzschild has discovered is that any mass, 332 00:17:41,594 --> 00:17:44,061 compressed into a small enough space, 333 00:17:44,063 --> 00:17:47,865 creates what we today call a black hole. 334 00:17:50,303 --> 00:17:51,902 But Albert Einstein-- 335 00:17:51,904 --> 00:17:54,872 whose own theory of gravity predicts such a thing-- 336 00:17:54,874 --> 00:17:58,742 cannot believe it can happen in the real world. 337 00:17:58,744 --> 00:18:00,411 BARTUSIAK: Einstein didn't think 338 00:18:00,413 --> 00:18:02,413 that nature would act like this. 339 00:18:02,415 --> 00:18:04,214 He didn't like this idea. 340 00:18:04,216 --> 00:18:10,788 LEVIN: Karl Schwarzschild becomes ill and dies before he has a chance 341 00:18:10,790 --> 00:18:15,259 to further investigate his own discovery. 342 00:18:15,261 --> 00:18:17,361 (crowd cheering) 343 00:18:17,363 --> 00:18:21,565 LEVIN: Two-and-a-half years later, in November 1918, 344 00:18:21,567 --> 00:18:23,667 World War I ends. 345 00:18:23,669 --> 00:18:28,105 The strange theoretical sphere discovered by Karl Schwarzschild 346 00:18:28,107 --> 00:18:30,708 seems destined to be forgotten-- 347 00:18:30,710 --> 00:18:34,445 nothing but a curious historical footnote. 348 00:18:34,447 --> 00:18:38,148 (explosion echoes) 349 00:18:38,150 --> 00:18:39,516 But in the coming decades, 350 00:18:39,518 --> 00:18:42,186 physicists learn more about the atom 351 00:18:42,188 --> 00:18:47,591 and about how fusing atoms powers stars-- 352 00:18:47,593 --> 00:18:52,329 a process called nuclear fusion. 353 00:18:52,331 --> 00:18:55,766 Some begin to wonder if something like a black hole 354 00:18:55,768 --> 00:18:59,036 could actually come from a star. 355 00:19:00,973 --> 00:19:06,443 But not just any star-- it would have to be big. 356 00:19:06,445 --> 00:19:07,811 GLIKMAN: Stars are born in litters, 357 00:19:07,813 --> 00:19:10,681 and you get a distribution of sizes and masses; 358 00:19:10,683 --> 00:19:15,185 thousands of little stars 359 00:19:15,187 --> 00:19:17,654 and a few big stars, very big stars, 360 00:19:17,656 --> 00:19:19,256 incredibly massive. 361 00:19:20,459 --> 00:19:25,629 NIA IMARA: Stars are in many ways similar to living creatures. 362 00:19:25,631 --> 00:19:28,265 Like humans, they have life cycles. 363 00:19:28,267 --> 00:19:34,605 LEVIN: Investigating stars' life cycles in the 1930s, two visionaries-- 364 00:19:34,607 --> 00:19:38,575 Subramanyan Chandrasekhar and Robert Oppenheimer-- 365 00:19:38,577 --> 00:19:41,211 discover that the most massive stars 366 00:19:41,213 --> 00:19:45,783 end their lives very differently from smaller ones. 367 00:19:45,785 --> 00:19:48,886 The life cycle of a star really depends on its mass. 368 00:19:48,888 --> 00:19:53,424 The mass of a star determines what's going to happen 369 00:19:53,426 --> 00:19:57,094 after it finishes burning its hydrogen fuel. 370 00:19:57,096 --> 00:20:03,400 LEVIN: All stars start out burning hydrogen-- the lightest atom-- 371 00:20:03,402 --> 00:20:05,836 fusing hydrogen atoms into helium, 372 00:20:05,838 --> 00:20:10,774 working their way up to heavier elements. 373 00:20:10,776 --> 00:20:14,111 Gravity wants to crush the entire mass of the star, 374 00:20:14,113 --> 00:20:19,249 but the enormous energy released by fusion pushes outward, 375 00:20:19,251 --> 00:20:22,653 preventing the star from collapsing. 376 00:20:22,655 --> 00:20:26,056 IMARA: Stars are stable because you have an outward-moving pressure 377 00:20:26,058 --> 00:20:27,558 due to nuclear fusion, 378 00:20:27,560 --> 00:20:30,260 and that's balancing with the inward force of gravity. 379 00:20:33,065 --> 00:20:38,335 LEVIN: Smaller stars can't fuse elements heavier than helium. 380 00:20:38,337 --> 00:20:41,071 But in the most massive stars, 381 00:20:41,073 --> 00:20:45,175 fusion crushes heavier and heavier atoms 382 00:20:45,177 --> 00:20:48,412 all the way up to iron. 383 00:20:48,414 --> 00:20:52,049 Iron is such a massive element, it has so many protons in it, 384 00:20:52,051 --> 00:20:55,719 that by the time you fuse iron, 385 00:20:55,721 --> 00:20:58,689 you don't get any energy back out. 386 00:20:58,691 --> 00:21:01,225 LEVIN: Iron is a dead end for stars. 387 00:21:01,227 --> 00:21:04,628 Fusing atoms larger than iron 388 00:21:04,630 --> 00:21:07,831 doesn't release enough energy to support the star. 389 00:21:07,833 --> 00:21:10,234 And without enough energy from fusion 390 00:21:10,236 --> 00:21:12,169 keeping the star inflated, 391 00:21:12,171 --> 00:21:14,771 there's nothing to fight gravity. 392 00:21:14,773 --> 00:21:17,841 GLIKMAN: And gravity wins. 393 00:21:17,843 --> 00:21:20,444 And so the entire star collapses. 394 00:21:20,446 --> 00:21:26,483 LEVIN: Very rapidly, trillions of tons of material come crashing down, 395 00:21:26,485 --> 00:21:29,653 hit the dense core, and bounce back out, 396 00:21:29,655 --> 00:21:33,991 blowing off the outer layers of the star in a massive explosion: 397 00:21:33,993 --> 00:21:35,826 (explosion roars) 398 00:21:35,828 --> 00:21:39,696 a supernova. 399 00:21:39,698 --> 00:21:41,899 The more mass, the more gravity. 400 00:21:41,901 --> 00:21:45,002 So if the remaining core is massive enough, 401 00:21:45,004 --> 00:21:47,771 gravity becomes unstoppable. 402 00:21:47,773 --> 00:21:49,273 TYSON: There's no known force 403 00:21:49,275 --> 00:21:54,177 to prevent the collapse to an infinitesimally small dot. 404 00:21:54,179 --> 00:21:56,079 (explosion roars) 405 00:21:56,081 --> 00:21:58,282 LEVIN: Gravity crushes the stellar core down, 406 00:21:58,284 --> 00:22:01,151 smaller and smaller and smaller, 407 00:22:01,153 --> 00:22:03,353 until all its mass is compressed 408 00:22:03,355 --> 00:22:07,991 in an infinitely small point: 409 00:22:07,993 --> 00:22:11,161 a black hole. 410 00:22:13,332 --> 00:22:14,932 The theory makes sense, 411 00:22:14,934 --> 00:22:20,137 but most physicists remain skeptical about black holes. 412 00:22:20,139 --> 00:22:23,106 NATARAJAN: Einstein and Eddington, all the sort of, you know, 413 00:22:23,108 --> 00:22:26,643 pre-eminent astrophysicists in the 1930s through 1950s, 414 00:22:26,645 --> 00:22:29,580 did not believe that they were actually real. 415 00:22:29,582 --> 00:22:33,116 It remained a solution, a mathematical enigma, 416 00:22:33,118 --> 00:22:34,685 for a very long time. 417 00:22:34,687 --> 00:22:37,287 So it took a long time for people 418 00:22:37,289 --> 00:22:39,990 to even start looking for them. 419 00:22:39,992 --> 00:22:42,826 LEVIN: It's not until the 1960s that the idea 420 00:22:42,828 --> 00:22:45,295 of a supernova creating a black hole 421 00:22:45,297 --> 00:22:48,799 is taken seriously. 422 00:22:48,801 --> 00:22:50,500 Princeton physicist John Wheeler, 423 00:22:50,502 --> 00:22:52,936 who had originally been a skeptic, 424 00:22:52,938 --> 00:22:55,105 begins to use a name from history 425 00:22:55,107 --> 00:22:57,874 for these invisible objects: 426 00:22:57,876 --> 00:23:00,744 black hole. 427 00:23:00,746 --> 00:23:03,480 The term "black hole" actually originates in India. 428 00:23:03,482 --> 00:23:07,284 The Black Hole was the name 429 00:23:07,286 --> 00:23:11,288 of an infamous prison in Calcutta. 430 00:23:13,092 --> 00:23:18,095 LEVIN: Still, no one has ever detected any sign of a black hole. 431 00:23:20,165 --> 00:23:24,234 Then, in 1967, graduate student Jocelyn Bell 432 00:23:24,236 --> 00:23:28,605 discovers a strange, extremely tiny dead star 433 00:23:28,607 --> 00:23:30,774 that gives off very little light-- 434 00:23:30,776 --> 00:23:34,378 a neutron star. 435 00:23:34,380 --> 00:23:36,680 The cold remains of a stellar collapse, 436 00:23:36,682 --> 00:23:39,850 the neutron star gives astronomers more confidence 437 00:23:39,852 --> 00:23:43,153 that black holes-- much heavier dead stars-- 438 00:23:43,155 --> 00:23:46,556 might also exist. 439 00:23:46,558 --> 00:23:48,525 (explosion roars) 440 00:23:48,527 --> 00:23:50,794 A half-century after Karl Schwarzschild 441 00:23:50,796 --> 00:23:53,463 mathematically showed that black holes 442 00:23:53,465 --> 00:23:55,966 were theoretically possible, 443 00:23:55,968 --> 00:23:59,236 scientists have identified a natural process 444 00:23:59,238 --> 00:24:04,541 that might create them: the death of large stars. 445 00:24:04,543 --> 00:24:06,376 So these giant supernova explosions 446 00:24:06,378 --> 00:24:08,412 of extremely massive stars 447 00:24:08,414 --> 00:24:09,813 make black holes. 448 00:24:09,815 --> 00:24:12,315 NATARAJAN: Any star that is born with a mass 449 00:24:12,317 --> 00:24:15,752 that's about ten times the mass of the sun or higher, 450 00:24:15,754 --> 00:24:18,789 will end in a black hole. 451 00:24:18,791 --> 00:24:22,392 So our galaxy is replete with little black holes, 452 00:24:22,394 --> 00:24:25,328 which are the stellar corpses of generations of stars 453 00:24:25,330 --> 00:24:28,532 that have come and gone. 454 00:24:28,534 --> 00:24:33,704 LEVIN: So what are these invisible stellar corpses like? 455 00:24:36,308 --> 00:24:39,042 Imagine I'm exploring space 456 00:24:39,044 --> 00:24:42,612 with some advanced technology for interstellar travel, 457 00:24:42,614 --> 00:24:45,582 so that we could visit a black hole-- 458 00:24:45,584 --> 00:24:48,485 maybe one in our own galactic neighborhood. 459 00:24:53,192 --> 00:24:55,859 This particular black hole isn't very big, 460 00:24:55,861 --> 00:24:57,728 only about ten solar masses-- 461 00:24:57,730 --> 00:25:00,330 meaning ten times the mass of the sun. 462 00:25:00,332 --> 00:25:04,134 And like all black holes, it has an event horizon-- 463 00:25:04,136 --> 00:25:07,471 a distinct edge to the darkness. 464 00:25:07,473 --> 00:25:10,340 That's the boundary Karl Schwarzschild first discovered, 465 00:25:10,342 --> 00:25:14,311 where gravity is so strong that nothing can escape-- 466 00:25:14,313 --> 00:25:15,812 not even light. 467 00:25:15,814 --> 00:25:17,914 And that's where we're going. 468 00:25:17,916 --> 00:25:20,417 (engine runs, machine chirps) 469 00:25:20,419 --> 00:25:26,056 ♪ ♪ 470 00:25:28,527 --> 00:25:34,431 ♪ ♪ 471 00:25:34,433 --> 00:25:39,402 LEVIN: As we get closer, some very strange things begin to happen. 472 00:25:41,140 --> 00:25:43,507 Look at the edge of the black hole-- 473 00:25:43,509 --> 00:25:45,408 see how the image of distant stars 474 00:25:45,410 --> 00:25:48,879 is distorted and smeared into a circle? 475 00:25:48,881 --> 00:25:51,815 That's gravitational lensing. 476 00:25:51,817 --> 00:25:54,017 The black hole's extreme gravity 477 00:25:54,019 --> 00:25:56,586 bends the path of light passing by, 478 00:25:56,588 --> 00:25:59,689 so that a single point of light, like a star, 479 00:25:59,691 --> 00:26:04,227 briefly appears as a ring around the event horizon. 480 00:26:04,229 --> 00:26:07,798 ♪ ♪ 481 00:26:07,800 --> 00:26:10,767 I'm now deep in the black hole's gravity well, 482 00:26:10,769 --> 00:26:13,403 and we're going to start experiencing the effects. 483 00:26:13,405 --> 00:26:17,774 The extreme gravity actually slows down time 484 00:26:17,776 --> 00:26:19,109 relative to the Earth. 485 00:26:19,111 --> 00:26:21,244 From their point of view... 486 00:26:21,246 --> 00:26:24,981 (audio slows): I appear to be slowing down. 487 00:26:24,983 --> 00:26:29,686 But from my point of view, time on Earth is speeding up. 488 00:26:33,759 --> 00:26:36,827 Now, let's say I want to get even closer, 489 00:26:36,829 --> 00:26:38,428 by taking a spacewalk. 490 00:26:38,430 --> 00:26:43,500 ♪ ♪ 491 00:26:48,640 --> 00:26:54,211 (machines beeping and hissing) 492 00:26:54,213 --> 00:26:56,513 The way the black hole slows down time 493 00:26:56,515 --> 00:26:58,949 is about to get even more pronounced. 494 00:26:58,951 --> 00:27:03,220 To keep track of the changes I'm about to experience, 495 00:27:03,222 --> 00:27:05,655 I'm turning on this strobe light. 496 00:27:05,657 --> 00:27:07,991 It'll blink once a second. 497 00:27:07,993 --> 00:27:13,263 From here, I can see the shadow of the event horizon approaching 498 00:27:13,265 --> 00:27:15,599 and my light blinking normally. 499 00:27:15,601 --> 00:27:17,968 But watching from the ship, 500 00:27:17,970 --> 00:27:20,937 the closer I move toward the black hole, 501 00:27:20,939 --> 00:27:23,240 the more slowly I appear to move. 502 00:27:23,242 --> 00:27:27,978 The pulses are nearly infinitely spaced, 503 00:27:27,980 --> 00:27:32,849 so it looks as though I'm frozen in time. 504 00:27:32,851 --> 00:27:36,119 For me, everything is completely normal. 505 00:27:36,121 --> 00:27:38,655 Even when I reach the event horizon. 506 00:27:41,126 --> 00:27:42,359 If you waited long enough-- 507 00:27:42,361 --> 00:27:46,529 maybe millions or billions of years-- 508 00:27:46,531 --> 00:27:49,633 the ship would finally see me disappear. 509 00:27:49,635 --> 00:27:53,536 And that's the last you'd see of me. 510 00:27:57,142 --> 00:27:59,609 What's inside a black hole? 511 00:27:59,611 --> 00:28:01,211 That's still a mystery. 512 00:28:01,213 --> 00:28:05,348 And even if I find out, I can never go back and tell you. 513 00:28:05,350 --> 00:28:09,953 But I can say this: black holes may be dark from the outside, 514 00:28:09,955 --> 00:28:12,622 but inside, they can be bright. 515 00:28:12,624 --> 00:28:15,091 I can watch the light from the galaxy 516 00:28:15,093 --> 00:28:17,327 that's fallen in behind me. 517 00:28:17,329 --> 00:28:20,764 And that's the last thing I'll ever see. 518 00:28:20,766 --> 00:28:23,700 Unfortunately, the fun is about to end. 519 00:28:23,702 --> 00:28:27,804 ♪ ♪ 520 00:28:27,806 --> 00:28:30,106 Now that I've crossed the event horizon, 521 00:28:30,108 --> 00:28:32,275 I'm falling toward the center, 522 00:28:32,277 --> 00:28:36,313 where all of the mass of the black hole is concentrated. 523 00:28:36,315 --> 00:28:40,250 And I'm beginning to get stretched. 524 00:28:40,252 --> 00:28:44,521 As I fall in, the gravitational pull at my feet 525 00:28:44,523 --> 00:28:46,289 is stronger than at my head, 526 00:28:46,291 --> 00:28:49,526 and my body is starting to get pulled apart. 527 00:28:49,528 --> 00:28:52,062 I'll be stretched as long and thin as a noodle-- 528 00:28:52,064 --> 00:28:53,663 spaghettified. 529 00:28:53,665 --> 00:28:55,665 And ultimately, I'll end up 530 00:28:55,667 --> 00:28:59,336 completely disintegrating into my fundamental particles, 531 00:28:59,338 --> 00:29:02,439 which are then crushed to an infinitely small point. 532 00:29:06,211 --> 00:29:09,112 A singularity, where everything we understand 533 00:29:09,114 --> 00:29:13,550 about space and time breaks down. 534 00:29:13,552 --> 00:29:15,618 Or maybe the black hole-- 535 00:29:15,620 --> 00:29:18,755 less than 40 miles across on the outside-- 536 00:29:18,757 --> 00:29:24,194 is as big as a universe on the inside. 537 00:29:24,196 --> 00:29:25,595 And as I pass through, 538 00:29:25,597 --> 00:29:28,531 my particles will join the primordial soup 539 00:29:28,533 --> 00:29:30,567 of a new beginning. 540 00:29:35,974 --> 00:29:39,009 So that's what theory tells us we might experience 541 00:29:39,011 --> 00:29:41,444 if we could travel to a black hole. 542 00:29:41,446 --> 00:29:46,316 ♪ ♪ 543 00:29:48,954 --> 00:29:52,956 ♪ ♪ 544 00:29:54,092 --> 00:29:56,226 But how can we know for sure? 545 00:29:56,228 --> 00:30:00,130 How do you investigate something you can't even see? 546 00:30:02,434 --> 00:30:04,034 There are ways to investigate 547 00:30:04,036 --> 00:30:06,603 if something is happening somewhere, 548 00:30:06,605 --> 00:30:10,407 even if I can't see that thing directly. 549 00:30:10,409 --> 00:30:11,641 Take Yankee Stadium: 550 00:30:11,643 --> 00:30:14,344 what's happening inside there? 551 00:30:14,346 --> 00:30:15,712 Is there a game going on? 552 00:30:15,714 --> 00:30:17,380 I can't see the field. 553 00:30:17,382 --> 00:30:20,683 I can't see any players, or baseballs, or bats. 554 00:30:20,685 --> 00:30:22,252 But I can definitely tell 555 00:30:22,254 --> 00:30:24,687 if there's activity around the park. 556 00:30:27,492 --> 00:30:29,259 It's pretty clear something is going on. 557 00:30:29,261 --> 00:30:32,195 ♪ ♪ 558 00:30:32,197 --> 00:30:34,964 It might seem obvious, but whatever it is, 559 00:30:34,966 --> 00:30:38,234 I can learn a lot just by observing the happenings 560 00:30:38,236 --> 00:30:39,602 around the stadium. 561 00:30:43,308 --> 00:30:45,141 And these do look a lot like baseball fans. 562 00:30:45,143 --> 00:30:49,179 ♪ ♪ 563 00:30:49,181 --> 00:30:50,280 (bat hits ball) 564 00:30:50,282 --> 00:30:52,048 (crowd cheers, organ plays) 565 00:30:52,050 --> 00:30:55,652 And that's the way we investigate black holes: 566 00:30:55,654 --> 00:31:00,557 by observing the effect they have on their surroundings. 567 00:31:00,559 --> 00:31:04,194 But what sort of effects? 568 00:31:04,196 --> 00:31:07,831 How might a black hole reveal itself? 569 00:31:07,833 --> 00:31:11,501 Starting just before World War II, 570 00:31:11,503 --> 00:31:13,236 two monumental discoveries 571 00:31:13,238 --> 00:31:16,272 are about to radically change astronomy. 572 00:31:16,274 --> 00:31:22,045 In 1931, Bell Labs engineer Karl Jansky 573 00:31:22,047 --> 00:31:27,016 picks up mysterious radio waves emanating from deep space. 574 00:31:27,018 --> 00:31:30,487 Then the sky gets even stranger-- 575 00:31:30,489 --> 00:31:33,690 when scientists mount Geiger counters 576 00:31:33,692 --> 00:31:35,391 on captured German rockets 577 00:31:35,393 --> 00:31:39,963 and discover the cosmos is also full of X-rays. 578 00:31:43,235 --> 00:31:47,437 These discoveries give astronomers important new tools 579 00:31:47,439 --> 00:31:49,939 that will revolutionize the hunt for black holes 580 00:31:49,941 --> 00:31:52,408 and dramatically expand our vision. 581 00:31:52,410 --> 00:31:53,610 (machine beeping) 582 00:31:53,612 --> 00:31:56,212 BARTUSIAK: What our eyes can perceive 583 00:31:56,214 --> 00:32:01,084 is a very narrow part of the electromagnetic spectrum. 584 00:32:03,155 --> 00:32:05,288 LEVIN: If the electromagnetic spectrum 585 00:32:05,290 --> 00:32:07,123 were laid out along the Brooklyn Bridge, 586 00:32:07,125 --> 00:32:09,292 the portion we can see with our eyes 587 00:32:09,294 --> 00:32:12,495 would be just a few feet wide. 588 00:32:12,497 --> 00:32:14,063 Electromagnetic radiation 589 00:32:14,065 --> 00:32:17,667 includes waves of many different frequencies: 590 00:32:17,669 --> 00:32:23,673 radio waves, microwaves, infrared and ultraviolet light, 591 00:32:23,675 --> 00:32:27,143 X-rays, and gamma rays. 592 00:32:29,181 --> 00:32:32,448 Radio and X-ray astronomy open up the sky, 593 00:32:32,450 --> 00:32:35,084 revealing dim or even invisible objects 594 00:32:35,086 --> 00:32:39,689 blasting out powerful energy no one knew was there. 595 00:32:39,691 --> 00:32:41,057 They began to realize 596 00:32:41,059 --> 00:32:43,293 that this very placid thing that we see out there, 597 00:32:43,295 --> 00:32:47,096 all this very quiet thing that looks like nothing is happening 598 00:32:47,098 --> 00:32:49,866 and the only thing that's moving is the planets, 599 00:32:49,868 --> 00:32:51,201 found out that there was madness going out there. 600 00:32:51,203 --> 00:32:52,769 It was chaos out there! 601 00:32:52,771 --> 00:32:58,341 LEVIN: X-rays come from the high-energy end of the spectrum. 602 00:33:00,745 --> 00:33:04,747 What is creating all this energy? 603 00:33:04,749 --> 00:33:07,450 This much thing is certain: whatever the source, 604 00:33:07,452 --> 00:33:10,119 it is invisible to ordinary telescopes. 605 00:33:10,121 --> 00:33:12,488 And it is hot. 606 00:33:12,490 --> 00:33:13,790 PAUL MURDIN: X-rays come from things 607 00:33:13,792 --> 00:33:17,126 which are at temperatures of millions of degrees. 608 00:33:17,128 --> 00:33:18,461 Even tens of millions. 609 00:33:18,463 --> 00:33:21,197 LEVIN: One of the first of these X-ray sources 610 00:33:21,199 --> 00:33:22,932 to catch the attention of astronomers 611 00:33:22,934 --> 00:33:25,602 is named Cygnus X-1. 612 00:33:25,604 --> 00:33:28,304 Cygnus, it was in the constellation Cygnus; 613 00:33:28,306 --> 00:33:29,872 X, it was an x-ray source; 614 00:33:29,874 --> 00:33:31,874 one, it was the first one you found. 615 00:33:33,211 --> 00:33:37,247 LEVIN: In 1970, Paul Murdin is a young English astronomer 616 00:33:37,249 --> 00:33:39,549 trying to secure his next job. 617 00:33:39,551 --> 00:33:40,850 MURDIN: I was a research fellow, 618 00:33:40,852 --> 00:33:43,620 I was coming to the end of my three-year contract, 619 00:33:43,622 --> 00:33:46,990 and I thought, "What can I contribute to finding out 620 00:33:46,992 --> 00:33:48,458 what these things are?" 621 00:33:48,460 --> 00:33:51,060 ♪ ♪ 622 00:33:51,062 --> 00:33:54,364 LEVIN: Murdin works in a 15th-century castle 623 00:33:54,366 --> 00:33:57,200 surrounded by telescopes-- 624 00:33:57,202 --> 00:34:00,503 the Royal Observatory. 625 00:34:00,505 --> 00:34:03,773 Using the largest telescope in England, 626 00:34:03,775 --> 00:34:05,441 he begins searching the area 627 00:34:05,443 --> 00:34:09,345 of the constellation Cygnus, the swan. 628 00:34:09,347 --> 00:34:13,983 He decides to hunt for pairs of stars. 629 00:34:13,985 --> 00:34:17,420 Pairs of stars are called binaries. 630 00:34:17,422 --> 00:34:21,658 They may sound exotic, but they're not at all uncommon. 631 00:34:21,660 --> 00:34:25,228 Many of the stars we see-- perhaps half-- 632 00:34:25,230 --> 00:34:27,263 are actually binaries, 633 00:34:27,265 --> 00:34:30,933 pairs of orbiting stars locked together by gravity. 634 00:34:30,935 --> 00:34:36,406 But Murdin wonders: Is it possible there are binaries 635 00:34:36,408 --> 00:34:39,976 where only one of the stars is visible? 636 00:34:39,978 --> 00:34:43,146 MURDIN: I thought that maybe there was a kind of a star system 637 00:34:43,148 --> 00:34:47,717 in which there was a star, one ordinary star that made light, 638 00:34:47,719 --> 00:34:50,286 and then there was another star nearby that made X-rays. 639 00:34:50,288 --> 00:34:53,923 LEVIN: The telltale sign of a binary 640 00:34:53,925 --> 00:34:57,860 is that the stars are moving around each other. 641 00:34:57,862 --> 00:35:01,097 So Murdin begins searching for a visible star 642 00:35:01,099 --> 00:35:02,865 that shows signs of motion. 643 00:35:02,867 --> 00:35:06,002 Sometimes it's coming towards you, sometimes it's coming away. 644 00:35:06,004 --> 00:35:08,071 Sometimes it's coming towards you, sometimes it's coming away. 645 00:35:08,073 --> 00:35:13,276 LEVIN: When the star is moving toward us, it appears more blue, 646 00:35:13,278 --> 00:35:18,181 as the wavelength of its light gets shorter. 647 00:35:18,183 --> 00:35:20,283 Moving away, it appears more red, 648 00:35:20,285 --> 00:35:24,854 as the wavelength of its light gets longer. 649 00:35:24,856 --> 00:35:28,324 This is known as Doppler shift. 650 00:35:28,326 --> 00:35:30,793 After looking for color changes 651 00:35:30,795 --> 00:35:33,863 in hundreds of stars in the area of Cygnus, 652 00:35:33,865 --> 00:35:36,699 Murdin spots a possible suspect-- 653 00:35:36,701 --> 00:35:39,969 a visible star whose light is shifting, 654 00:35:39,971 --> 00:35:42,739 as though moving around. 655 00:35:42,741 --> 00:35:47,110 MURDIN: It very clearly was a binary star, a double star. 656 00:35:47,112 --> 00:35:50,780 The star was moving around and around with a period, 657 00:35:50,782 --> 00:35:54,050 going around once, every 5.6 days. 658 00:35:56,688 --> 00:36:00,289 LEVIN: But whatever it's going around can't be seen. 659 00:36:00,291 --> 00:36:03,893 MURDIN: There was no trace in the spectrum of the second star. 660 00:36:03,895 --> 00:36:05,061 There was one star there. 661 00:36:05,063 --> 00:36:06,763 There wasn't the second star there. 662 00:36:06,765 --> 00:36:13,503 LEVIN: Murdin has a binary pair in which only one star is visible. 663 00:36:13,505 --> 00:36:15,605 The second object emits X-rays, 664 00:36:15,607 --> 00:36:19,609 has enough mass and gravity to dramatically move a star, 665 00:36:19,611 --> 00:36:22,979 but gives off no light. 666 00:36:22,981 --> 00:36:24,781 Could it be the corpse of a star 667 00:36:24,783 --> 00:36:28,718 massive enough to become a black hole? 668 00:36:28,720 --> 00:36:30,553 KIP THORNE: The crucial issue in deciding 669 00:36:30,555 --> 00:36:32,855 whether Cygnus X-1 was a black hole 670 00:36:32,857 --> 00:36:37,160 was to measure the mass of the X-ray-emitting object. 671 00:36:37,162 --> 00:36:40,530 LEVIN: It would have to be very massive, 672 00:36:40,532 --> 00:36:43,800 at least three times the mass of our sun. 673 00:36:43,802 --> 00:36:46,903 If not, it's probably just a neutron star-- 674 00:36:46,905 --> 00:36:50,339 a collapsed star that's dense, 675 00:36:50,341 --> 00:36:53,509 but not heavy enough to be a black hole. 676 00:36:53,511 --> 00:36:58,114 THORNE: So the observers needed to come up with a conclusion 677 00:36:58,116 --> 00:36:59,315 that the dark object, 678 00:36:59,317 --> 00:37:03,686 the X-ray-emitting object in Cygnus X-1, 679 00:37:03,688 --> 00:37:05,621 was heavier, hopefully substantially heavier, 680 00:37:05,623 --> 00:37:07,356 than three solar masses. 681 00:37:07,358 --> 00:37:11,461 LEVIN: From his observations, Murdin is able to make an estimate 682 00:37:11,463 --> 00:37:14,497 of the mass of the invisible partner. 683 00:37:14,499 --> 00:37:20,002 And the answer came out to be six times the mass of the sun. 684 00:37:20,004 --> 00:37:23,105 So there was a story, then, 685 00:37:23,107 --> 00:37:26,142 that Cygnus X-1 was a black hole. 686 00:37:26,144 --> 00:37:28,778 And the key to the argument was 687 00:37:28,780 --> 00:37:31,414 that the mass of the star you couldn't see 688 00:37:31,416 --> 00:37:33,349 was more than three solar masses. 689 00:37:33,351 --> 00:37:37,320 When I'd finished writing it all out, I sat back and thought, 690 00:37:37,322 --> 00:37:40,656 "It's a black hole." 691 00:37:40,658 --> 00:37:43,359 ♪ ♪ 692 00:37:43,361 --> 00:37:47,864 LEVIN: This would be the first actual detection of a black hole. 693 00:37:47,866 --> 00:37:52,435 It's a huge claim, and Murdin will have to convince skeptics, 694 00:37:52,437 --> 00:37:55,204 starting with his boss. 695 00:37:55,206 --> 00:37:58,508 MURDIN: The Astronomer Royal, Sir Richard Woolley. 696 00:37:58,510 --> 00:38:00,276 He didn't really go for black holes. 697 00:38:00,278 --> 00:38:03,246 "It's all fanciful..." 698 00:38:03,248 --> 00:38:05,181 It's kind of-- a lot of people in California 699 00:38:05,183 --> 00:38:06,482 were talking about this. 700 00:38:06,484 --> 00:38:09,051 There are a lot of funny people in California. 701 00:38:09,053 --> 00:38:13,689 (chuckles): You know, a lot of hippie-type people. 702 00:38:13,691 --> 00:38:17,159 LEVIN: People like theorist Kip Thorne. 703 00:38:17,161 --> 00:38:18,494 So I was nervous about it. 704 00:38:18,496 --> 00:38:21,297 I was nervous about the scale of the discovery. 705 00:38:21,299 --> 00:38:23,833 And actually so were other people all around me. 706 00:38:23,835 --> 00:38:30,573 I was working with a fellow scientist, Louise Webster. 707 00:38:30,575 --> 00:38:33,676 And we were modest about the claim that we were making 708 00:38:33,678 --> 00:38:36,279 because we knew what people would think of it. 709 00:38:36,281 --> 00:38:38,781 And if you look at the paper we published, 710 00:38:38,783 --> 00:38:43,619 it just mentions the word "black hole" once, right at the end. 711 00:38:43,621 --> 00:38:45,621 "We think this might be a black hole." 712 00:38:45,623 --> 00:38:52,762 LEVIN: The Paul Murdin-Louise Webster paper appears in September 1971. 713 00:38:52,764 --> 00:38:57,600 Other astronomers agree: It could be a black hole. 714 00:38:57,602 --> 00:39:00,236 But no one knows for sure. 715 00:39:02,340 --> 00:39:03,773 Three years later, 716 00:39:03,775 --> 00:39:07,209 Kip Thorne and the noted British physicist Stephen Hawking 717 00:39:07,211 --> 00:39:11,280 make a now-famous wager about Cygnus X-1. 718 00:39:11,282 --> 00:39:14,216 We made a bet as to whether Cygnus X-1 719 00:39:14,218 --> 00:39:15,318 really was a black hole or not. 720 00:39:15,320 --> 00:39:19,221 LEVIN: The bet is partly in jest. 721 00:39:19,223 --> 00:39:22,825 Both men hope it is a black hole. 722 00:39:22,827 --> 00:39:27,730 But Hawking, not wanting to jinx it, bets against his own wishes. 723 00:39:27,732 --> 00:39:30,633 THORNE: Stephen claims that Cygnus X-1 is not a black hole. 724 00:39:30,635 --> 00:39:33,135 And I claim it is a black hole. 725 00:39:33,137 --> 00:39:38,674 And so we signed that bet in December 1974. 726 00:39:38,676 --> 00:39:42,011 And gradually, the case that it really was a black hole 727 00:39:42,013 --> 00:39:44,380 became stronger and stronger and stronger. 728 00:39:44,382 --> 00:39:50,286 So in June of 1990, Stephen broke into my office 729 00:39:50,288 --> 00:39:53,889 and he thumb-printed off on this bet, 730 00:39:53,891 --> 00:39:55,524 conceded the bet in my absence. 731 00:39:55,526 --> 00:40:01,330 I came back from Russia and discovered that he had conceded. 732 00:40:01,332 --> 00:40:06,802 LEVIN: Now, by 1990, the evidence of Cygnus X-1's mass 733 00:40:06,804 --> 00:40:10,906 may be strg enough to settle a bet between two friends. 734 00:40:10,908 --> 00:40:15,544 But the original estimate wasn't precise enough to be definitive. 735 00:40:15,546 --> 00:40:18,347 In order to calculate mass, 736 00:40:18,349 --> 00:40:21,350 Paul Murdin had to rely on rough estimates 737 00:40:21,352 --> 00:40:23,853 of the distance to Cygnus X-1, 738 00:40:23,855 --> 00:40:26,122 which varied by a factor of ten. 739 00:40:26,124 --> 00:40:30,059 And the question wouldn't be answered for another 20 years, 740 00:40:30,061 --> 00:40:34,430 until astronomer Mark Reid became intrigued by the puzzle. 741 00:40:34,432 --> 00:40:37,166 Reid is an astronomer 742 00:40:37,168 --> 00:40:40,636 at the Harvard-Smithsonian Center for Astrophysics 743 00:40:40,638 --> 00:40:42,838 when he sets out to conclusively prove 744 00:40:42,840 --> 00:40:45,241 that Cygnus X-1 is a black hole 745 00:40:45,243 --> 00:40:47,910 by measuring its precise mass. 746 00:40:49,914 --> 00:40:53,816 But how can you measure the mass of an invisible object? 747 00:40:53,818 --> 00:40:55,418 Using laws developed 748 00:40:55,420 --> 00:40:57,953 by German astronomer Johannes Kepler 749 00:40:57,955 --> 00:40:59,822 in the 1600s, 750 00:40:59,824 --> 00:41:03,626 it's possible to calculate the mass of a celestial object-- 751 00:41:03,628 --> 00:41:07,163 but only if you know its distance. 752 00:41:09,434 --> 00:41:11,967 REID: Distance in astronomy is absolutely fundamental. 753 00:41:11,969 --> 00:41:14,937 If you don't know distance, you don't know what the object is. 754 00:41:14,939 --> 00:41:18,708 It could be a very nearby firefly-like thing. 755 00:41:18,710 --> 00:41:21,377 It could be a very distant, huge star, 756 00:41:21,379 --> 00:41:23,846 much, much bigger than the sun. 757 00:41:23,848 --> 00:41:28,451 LEVIN: So to get the true, precise mass of Cygnus X-1-- 758 00:41:28,453 --> 00:41:31,520 and confirm that it is a black hole-- 759 00:41:31,522 --> 00:41:34,857 Reid needs to know how far away it is. 760 00:41:34,859 --> 00:41:39,028 But how can he measure the distance to a star? 761 00:41:39,030 --> 00:41:45,301 The secret lies in a familiar phenomenon: parallax. 762 00:41:45,303 --> 00:41:50,506 It's what our eyes and brains use to see in three dimensions. 763 00:41:50,508 --> 00:41:52,274 You can put your finger up at arm's length, 764 00:41:52,276 --> 00:41:56,112 look at it, and close one eye. 765 00:41:56,114 --> 00:41:57,379 I'm closing my left eye. 766 00:41:57,381 --> 00:41:58,581 And I'm looking at my finger 767 00:41:58,583 --> 00:42:01,984 relative to the wall in the background there. 768 00:42:01,986 --> 00:42:04,086 And now if I open my eye, close my right eye, 769 00:42:04,088 --> 00:42:08,124 I see my finger has appeared to move 770 00:42:08,126 --> 00:42:10,359 with respect to the original position. 771 00:42:10,361 --> 00:42:12,328 And that's because our eyes are separated, 772 00:42:12,330 --> 00:42:14,630 and we view from different vantage points. 773 00:42:14,632 --> 00:42:17,133 LEVIN: To use parallax 774 00:42:17,135 --> 00:42:19,702 to measure distance to an object in the sky, 775 00:42:19,704 --> 00:42:21,804 astronomers let the motion of the Earth 776 00:42:21,806 --> 00:42:25,775 provide the two different vantage points. 777 00:42:25,777 --> 00:42:29,478 Imagine Cygnus X-1 is right here. 778 00:42:29,480 --> 00:42:32,348 And the Earth and the sun are over there. 779 00:42:32,350 --> 00:42:35,951 Now, the Earth goes around the sun once a year. 780 00:42:35,953 --> 00:42:40,422 And in the springtime, the Earth ends up on one side of the sun, 781 00:42:40,424 --> 00:42:44,627 and we observe Cygnus X-1 along a ray path like this. 782 00:42:46,230 --> 00:42:49,932 Then six months later, the Earth goes around the sun 783 00:42:49,934 --> 00:42:52,301 to the other side. 784 00:42:52,303 --> 00:42:54,870 We get a different vantage point from Cygnus X-1. 785 00:42:57,542 --> 00:42:59,708 LEVIN: Now he has a triangle that goes 786 00:42:59,710 --> 00:43:02,178 between the Earth at its two positions 787 00:43:02,180 --> 00:43:06,015 and Cygnus X-1. 788 00:43:06,017 --> 00:43:07,716 We know the base of the triangle, 789 00:43:07,718 --> 00:43:10,820 the diameter of Earth's orbit. 790 00:43:10,822 --> 00:43:12,988 And the principles of geometry tell us 791 00:43:12,990 --> 00:43:15,858 that all we need to calculate the distance 792 00:43:15,860 --> 00:43:18,494 is the size of the angle at the top. 793 00:43:18,496 --> 00:43:21,163 And we measure this very small angle here, 794 00:43:21,165 --> 00:43:22,965 at the point at Cygnus X-1. 795 00:43:22,967 --> 00:43:24,767 And then from direct geometry, 796 00:43:24,769 --> 00:43:27,670 we can calculate the distance to Cygnus X-1 797 00:43:27,672 --> 00:43:29,972 and from that infer a very accurate mass. 798 00:43:29,974 --> 00:43:33,175 LEVIN: The concept is simple. 799 00:43:33,177 --> 00:43:35,811 But Cygnus X-1 is so far away 800 00:43:35,813 --> 00:43:38,948 that the angle to be measured is miniscule-- 801 00:43:38,950 --> 00:43:41,884 a tiny fraction of one degree. 802 00:43:41,886 --> 00:43:44,987 It's smaller than the angle spanned 803 00:43:44,989 --> 00:43:46,989 by Abraham Lincoln's nose 804 00:43:46,991 --> 00:43:52,394 on a penny in San Francisco viewed from New York. 805 00:43:53,898 --> 00:43:56,832 Because the angle is so very tiny, 806 00:43:56,834 --> 00:44:00,236 it can't be measured by any one telescope. 807 00:44:00,238 --> 00:44:04,306 But Reid's team has a solution. 808 00:44:04,308 --> 00:44:06,208 We take ten radio telescopes 809 00:44:06,210 --> 00:44:09,144 that are spread across the continental U.S. 810 00:44:09,146 --> 00:44:13,749 and to Hawaii and to St. Croix in the Virgin Islands. 811 00:44:13,751 --> 00:44:16,418 We use these telescopes simultaneously, 812 00:44:16,420 --> 00:44:19,655 and we synthesize in a computer 813 00:44:19,657 --> 00:44:23,125 a telescope that has a diameter of the size of the Earth. 814 00:44:23,127 --> 00:44:25,794 That gives you incredible angular resolution. 815 00:44:25,796 --> 00:44:29,298 LEVIN: Using this technique, Reid's team determines 816 00:44:29,300 --> 00:44:33,936 that Cygnus X-1 is 6,000 light years away. 817 00:44:33,938 --> 00:44:37,539 REID: With the new distance we got, the 6,000-light-year distance, 818 00:44:37,541 --> 00:44:39,508 we're able to determine that the mass 819 00:44:39,510 --> 00:44:42,211 is about 15 solar masses, 820 00:44:42,213 --> 00:44:44,179 easily a black hole. 821 00:44:47,852 --> 00:44:51,553 LEVIN: 40 years after it was identified as a possibility, 822 00:44:51,555 --> 00:44:55,724 Cygnus X-1 is now widely accepted 823 00:44:55,726 --> 00:44:58,227 as the first confirmed black hole. 824 00:44:58,229 --> 00:44:59,561 MURDIN: It's an understated paper, 825 00:44:59,563 --> 00:45:01,497 and the fact that my name was on it 826 00:45:01,499 --> 00:45:03,098 and Louise Webster's was on it, 827 00:45:03,100 --> 00:45:05,401 did us a lot of good in our careers. 828 00:45:05,403 --> 00:45:08,170 I think as a result of this discovery, 829 00:45:08,172 --> 00:45:09,538 I got offered a permanent job. 830 00:45:09,540 --> 00:45:12,241 And it was a great celebration for the family. 831 00:45:12,243 --> 00:45:15,277 So it worked out very well for me-- 832 00:45:15,279 --> 00:45:18,414 as well as getting the intellectual satisfaction 833 00:45:18,416 --> 00:45:20,149 of solving a problem. 834 00:45:20,151 --> 00:45:25,988 LEVIN: So finally, after years of speculation, 835 00:45:25,990 --> 00:45:28,390 we have a real black hole. 836 00:45:28,392 --> 00:45:32,928 Not only that, but a black hole that's blasting out X-rays 837 00:45:32,930 --> 00:45:35,431 and has a companion star. 838 00:45:35,433 --> 00:45:39,802 If we could visit in my imaginary spaceship, 839 00:45:39,804 --> 00:45:43,605 what would we see? 840 00:45:46,243 --> 00:45:48,077 The distance to Cygnus X-1 841 00:45:48,079 --> 00:45:52,681 has been established at 6,000 light years from Earth. 842 00:45:52,683 --> 00:45:58,787 And its mass is 15 solar masses, or 15 times the mass of the sun. 843 00:45:58,789 --> 00:46:05,361 And Cygnus X-1 is surrounded by an accretion disk-- 844 00:46:05,363 --> 00:46:10,699 a disk-shaped cloud of gas and dust outside its event horizon, 845 00:46:10,701 --> 00:46:12,301 the point of no return. 846 00:46:12,303 --> 00:46:15,471 As gravity pulls matter toward the black hole, 847 00:46:15,473 --> 00:46:17,573 the cloud starts rotating, 848 00:46:17,575 --> 00:46:22,344 just like water being pulled down a drain. 849 00:46:22,346 --> 00:46:24,313 Within that accretion disk, 850 00:46:24,315 --> 00:46:28,050 particles closest to the black hole whip around 851 00:46:28,052 --> 00:46:30,052 at half the speed of light. 852 00:46:30,054 --> 00:46:35,124 It's like a giant particle accelerator in space. 853 00:46:35,126 --> 00:46:38,961 But why does it emit X-rays? 854 00:46:38,963 --> 00:46:42,731 As those particles race around, they collide, 855 00:46:42,733 --> 00:46:45,501 which heats them up to millions of degrees. 856 00:46:45,503 --> 00:46:50,906 When they get that hot, particles blast out X-rays. 857 00:46:50,908 --> 00:46:54,576 And it's those X-rays that first led astronomer Paul Murdin 858 00:46:54,578 --> 00:46:58,647 to investigate this black hole nearly five decades ago. 859 00:46:58,649 --> 00:47:02,217 ♪ ♪ 860 00:47:02,219 --> 00:47:08,390 And there's something else about Cygnus that's different: 861 00:47:08,392 --> 00:47:12,027 It has a companion star. 862 00:47:12,029 --> 00:47:14,329 This blue super-giant star 863 00:47:14,331 --> 00:47:19,701 orbits the black hole once every 5.6 days. 864 00:47:19,703 --> 00:47:23,705 It orbits so close to Cygnus X-1 865 00:47:23,707 --> 00:47:26,875 that the black hole strips material off the star 866 00:47:26,877 --> 00:47:28,944 and pulls it into the accretion disk. 867 00:47:28,946 --> 00:47:32,081 Some of that material will cross the event horizon 868 00:47:32,083 --> 00:47:36,785 and get swallowed up, but not all of it. 869 00:47:36,787 --> 00:47:39,054 OZEL: Some of the stuff actually comes back out 870 00:47:39,056 --> 00:47:42,357 before ever entering the black hole. 871 00:47:42,359 --> 00:47:44,026 Kind of like a toddler eating: 872 00:47:44,028 --> 00:47:45,994 Half the pasta ends up on the floor, 873 00:47:45,996 --> 00:47:47,663 half of it may be on the ceiling, 874 00:47:47,665 --> 00:47:49,064 and some of it in the mouth. 875 00:47:49,967 --> 00:47:51,233 One of the most striking 876 00:47:51,235 --> 00:47:54,603 and enigmatic features of Cygnus X-1 877 00:47:54,605 --> 00:47:56,839 is its enormous jets. 878 00:47:56,841 --> 00:48:01,243 These beams of particles and radiation stream outward 879 00:48:01,245 --> 00:48:03,612 from Cygnus's north and south poles, 880 00:48:03,614 --> 00:48:05,881 perpendicular to the accretion disk. 881 00:48:05,883 --> 00:48:09,485 ♪ ♪ 882 00:48:09,487 --> 00:48:12,421 There's still a lot we don't know about these jets, 883 00:48:12,423 --> 00:48:16,792 but they are tightly focused and extremely powerful, 884 00:48:16,794 --> 00:48:19,862 blasting out at nearly the speed of light 885 00:48:19,864 --> 00:48:22,764 and extending well beyond Cygnus. 886 00:48:22,766 --> 00:48:26,768 OZEL: When gas gets to these high temperatures 887 00:48:26,770 --> 00:48:28,170 and produces the light, 888 00:48:28,172 --> 00:48:31,707 there's also a little bit of a magnetic field 889 00:48:31,709 --> 00:48:33,242 that forms around them. 890 00:48:33,244 --> 00:48:36,011 And we don't understand exactly how, 891 00:48:36,013 --> 00:48:37,479 but these magnetic fields 892 00:48:37,481 --> 00:48:41,817 help collimate these massive outflows from black holes, 893 00:48:41,819 --> 00:48:46,588 powerful hoses if you will, that just spew matter out. 894 00:48:50,094 --> 00:48:53,729 LEVIN: So that's Cygnus X-1, if we could see it up close-- 895 00:48:53,731 --> 00:48:57,533 a growing, feeding black hole with huge jets 896 00:48:57,535 --> 00:49:02,371 blasting particles way out into the universe. 897 00:49:02,373 --> 00:49:06,875 NATARAJAN: They're almost these breathing, 898 00:49:06,877 --> 00:49:09,444 fire-eating demons, if you will. 899 00:49:09,446 --> 00:49:12,714 They flicker, they have bursts; 900 00:49:12,716 --> 00:49:17,586 it's a very violent fireball, very active. 901 00:49:22,660 --> 00:49:26,295 LEVIN: What was once a bizarre mathematical curiosity 902 00:49:26,297 --> 00:49:28,263 has now become quite real. 903 00:49:28,265 --> 00:49:29,665 (explosion roars) 904 00:49:29,667 --> 00:49:32,000 After decades of skepticism, 905 00:49:32,002 --> 00:49:35,103 scientists now accept that burned-out corpses 906 00:49:35,105 --> 00:49:36,104 of large stars 907 00:49:36,106 --> 00:49:38,440 can trap light inside them, 908 00:49:38,442 --> 00:49:40,976 warp space and time around them, 909 00:49:40,978 --> 00:49:46,448 attract matter, and accelerate it to mind-boggling speeds. 910 00:49:46,450 --> 00:49:48,650 GALISON: Black holes seemed like such a radical idea 911 00:49:48,652 --> 00:49:51,119 that we shouldn't accept it. 912 00:49:51,121 --> 00:49:52,654 But bit by bit, the evidence for black holes 913 00:49:52,656 --> 00:49:55,290 has gotten stronger and stronger. 914 00:49:55,292 --> 00:49:58,927 And we've seen these amazing things. 915 00:49:58,929 --> 00:50:01,797 ♪ ♪ 916 00:50:01,799 --> 00:50:05,033 LEVIN: At least 20 black holes have been found in our galaxy, 917 00:50:05,035 --> 00:50:09,738 X-ray binaries, like Cnus X-1. 918 00:50:09,740 --> 00:50:13,108 And there are probably millions more 919 00:50:13,110 --> 00:50:14,476 of these massive stellar corpses 920 00:50:14,478 --> 00:50:18,280 in our galaxy alone. 921 00:50:18,282 --> 00:50:23,185 Still, a stunning surprise awaits. 922 00:50:23,187 --> 00:50:27,189 Everything astronomers think they know about black holes-- 923 00:50:27,191 --> 00:50:31,293 and much of what they believe about the universe itself-- 924 00:50:31,295 --> 00:50:34,696 will be upended by a shocking discovery. 925 00:50:38,035 --> 00:50:42,204 The revelations begin when radio telescope surveys of the sky 926 00:50:42,206 --> 00:50:46,275 detect mysterious hot spots emitting radio energy. 927 00:50:46,277 --> 00:50:50,078 (whirring) 928 00:50:50,080 --> 00:50:52,047 They were coming from what looked like stars. 929 00:50:52,049 --> 00:50:56,118 LEVIN: Because these objects resemble stars, 930 00:50:56,120 --> 00:50:59,288 but were discovered through radio signals, 931 00:50:59,290 --> 00:51:03,558 astronomers name them quasi-stellar radio sources-- 932 00:51:03,560 --> 00:51:04,960 quasars. 933 00:51:04,962 --> 00:51:08,563 But are they stars or not? 934 00:51:08,565 --> 00:51:10,932 The first step in investigating them 935 00:51:10,934 --> 00:51:15,304 is to figure out what they're made of. 936 00:51:15,306 --> 00:51:17,606 To do that, astronomers analyze 937 00:51:17,608 --> 00:51:20,809 the electromagnetic energy they emit. 938 00:51:20,811 --> 00:51:24,613 Every element has a unique spectral fingerprint. 939 00:51:24,615 --> 00:51:26,982 For example, carbon. 940 00:51:26,984 --> 00:51:28,884 Helium. 941 00:51:28,886 --> 00:51:30,786 Hydrogen. 942 00:51:30,788 --> 00:51:34,690 These lines reveal the chemical make-up of a star. 943 00:51:34,692 --> 00:51:38,527 But the spectrum of a quasar 944 00:51:38,529 --> 00:51:41,897 turns out to be incomprehensible. 945 00:51:41,899 --> 00:51:45,534 BARTUSIAK: They looked at it and it was gibberish. 946 00:51:45,536 --> 00:51:49,871 It didn't look like there were any emissions 947 00:51:49,873 --> 00:51:51,340 from elements that they knew. 948 00:51:51,342 --> 00:51:55,310 LEVIN: What are they missing? 949 00:51:55,312 --> 00:51:57,746 There has to be a clue somewhere. 950 00:51:57,748 --> 00:52:04,319 Finally, in 1963, Caltech astronomer Maarten Schmidt 951 00:52:04,321 --> 00:52:07,322 finds it hiding in plain sight. 952 00:52:07,324 --> 00:52:12,894 Buried in the quasar's spectrum is the fingerprint of hydrogen. 953 00:52:12,896 --> 00:52:16,064 He noticed something familiar, but it was in the wrong place. 954 00:52:16,066 --> 00:52:23,739 The fingerprints of hydrogen had been shifted way off to the red. 955 00:52:23,741 --> 00:52:27,442 LEVIN: It was hard to spot because the spectral lines of hydrogen 956 00:52:27,444 --> 00:52:30,779 were radically shifted toward the lower-frequency end 957 00:52:30,781 --> 00:52:32,647 of the spectrum. 958 00:52:32,649 --> 00:52:35,450 And that could only mean one thing. 959 00:52:35,452 --> 00:52:38,954 ♪ ♪ 960 00:52:38,956 --> 00:52:43,125 The quasar is moving away from us at fantastic speed. 961 00:52:44,461 --> 00:52:47,763 But astronomers have never before seen light shifted 962 00:52:47,765 --> 00:52:49,731 to such an extreme. 963 00:52:49,733 --> 00:52:52,267 (barking, audio slowing down) 964 00:52:52,269 --> 00:52:57,139 Like a familiar sound shifting too low to understand, 965 00:52:57,141 --> 00:53:01,076 the light from quasars has shifted to such a degree 966 00:53:01,078 --> 00:53:04,513 that hydrogen is unrecognizable. 967 00:53:04,515 --> 00:53:06,848 This extreme amount of shift 968 00:53:06,850 --> 00:53:11,486 means quasars are racing away from us at blinding speeds. 969 00:53:11,488 --> 00:53:13,188 The reason? 970 00:53:13,190 --> 00:53:15,090 It's the legacy of an event 971 00:53:15,092 --> 00:53:19,761 that occurred almost 14 billion years ago: the Big Bang. 972 00:53:19,763 --> 00:53:23,532 (explosion roars) 973 00:53:23,534 --> 00:53:28,003 The beginning of our universe. 974 00:53:28,005 --> 00:53:30,372 And ever since, the universe has been expanding, 975 00:53:30,374 --> 00:53:35,477 carrying with it all the objects it contains, including quasars. 976 00:53:35,479 --> 00:53:38,980 GLIKMAN: No one had ever seen anything moving away at that high speed. 977 00:53:38,982 --> 00:53:41,450 This made this object the furthest-away thing 978 00:53:41,452 --> 00:53:43,151 that had ever been seen, 979 00:53:43,153 --> 00:53:46,254 which meant the thing itself had to be so luminous, 980 00:53:46,256 --> 00:53:47,489 and you had to account for that. 981 00:53:49,126 --> 00:53:51,793 BARTUSIAK: Two billion light years away, putting out the energy 982 00:53:51,795 --> 00:53:54,796 of a trillion suns each second. 983 00:53:56,467 --> 00:54:00,469 What could possibly create that? 984 00:54:00,471 --> 00:54:03,205 No one had any idea what could be powering these things. 985 00:54:03,207 --> 00:54:05,807 Where could all of this energy come from? 986 00:54:05,809 --> 00:54:08,577 If you work out through calculations, 987 00:54:08,579 --> 00:54:10,378 it can't be chemical energy. 988 00:54:10,380 --> 00:54:12,581 (explosion roars) 989 00:54:12,583 --> 00:54:14,249 They knew it couldn't be nuclear energy. 990 00:54:14,251 --> 00:54:16,284 (explosion roars) 991 00:54:16,286 --> 00:54:20,288 LEVIN: There's no way a quasar could be a star. 992 00:54:20,290 --> 00:54:21,656 No amount of nuclear fusion 993 00:54:21,658 --> 00:54:25,460 could produce that much star power. 994 00:54:25,462 --> 00:54:28,396 The only engine that could possibly 995 00:54:28,398 --> 00:54:30,365 put out that much energy is gravity. 996 00:54:32,736 --> 00:54:34,135 LEVIN: Gravity. 997 00:54:34,137 --> 00:54:38,907 In everyday life, we can overcome gravity easily. 998 00:54:38,909 --> 00:54:43,311 But when concentrated to an extreme by a black hole, 999 00:54:43,313 --> 00:54:46,448 gravity is overwhelmingly powerful. 1000 00:54:46,450 --> 00:54:49,951 A handful of scientists start wondering: 1001 00:54:49,953 --> 00:54:54,322 Could quasars perhaps be powered by gravity engines? 1002 00:54:54,324 --> 00:54:57,726 What if the energy blasting out from quasars 1003 00:54:57,728 --> 00:55:02,731 is coming from bright accretion disks around black holes? 1004 00:55:02,733 --> 00:55:07,335 NATARAJAN: To produce that kind of energy, 1005 00:55:07,337 --> 00:55:09,204 that kind of brightness, 1006 00:55:09,206 --> 00:55:10,805 it has to involve a black hole. 1007 00:55:10,807 --> 00:55:14,809 LEVIN: But not just any black hole. 1008 00:55:14,811 --> 00:55:18,046 THORNE: Whatever was the source of the emission from a quasar 1009 00:55:18,048 --> 00:55:20,148 had to be massive. 1010 00:55:20,150 --> 00:55:21,917 How massive? 1011 00:55:21,919 --> 00:55:25,887 Well, millions or billions of times heavier than the sun. 1012 00:55:25,889 --> 00:55:31,426 LEVIN: Millions or billions of times heavier than the sun. 1013 00:55:31,428 --> 00:55:36,898 Cygnus X-1 is only 15 times the mass of the sun. 1014 00:55:36,900 --> 00:55:38,600 The black holes powering quasars 1015 00:55:38,602 --> 00:55:44,105 are an entirely different category of black hole: 1016 00:55:44,107 --> 00:55:45,941 supermassives. 1017 00:55:45,943 --> 00:55:49,878 ♪ ♪ 1018 00:55:49,880 --> 00:55:54,382 And they seem to be located in the centers of galaxies. 1019 00:55:58,589 --> 00:56:01,456 But what about our own galaxy? 1020 00:56:01,458 --> 00:56:06,695 Could there be any supermassive black holes closer to home? 1021 00:56:06,697 --> 00:56:09,598 The center, where any supermassive would be found, 1022 00:56:09,600 --> 00:56:13,234 lies in the direction of the constellation Sagittarius, 1023 00:56:13,236 --> 00:56:17,272 the Archer. 1024 00:56:17,274 --> 00:56:20,575 Now, Sagittarius isn't just any constellation. 1025 00:56:20,577 --> 00:56:23,011 It's in the direction of the center 1026 00:56:23,013 --> 00:56:24,846 of our own Milky Way Galaxy. 1027 00:56:24,848 --> 00:56:28,450 But since we live inside the Milky Way, 1028 00:56:28,452 --> 00:56:31,586 we can't see the galaxy the way a space traveler would. 1029 00:56:33,924 --> 00:56:37,859 But I can use my trusted imaginary star machine 1030 00:56:37,861 --> 00:56:40,462 to show us the galaxy from the outside. 1031 00:56:40,464 --> 00:56:45,467 Our home is a spiral galaxy, hundreds of billions of stars, 1032 00:56:45,469 --> 00:56:48,637 drawn together into a gigantic disk. 1033 00:56:48,639 --> 00:56:52,874 It's wide, about 100,000 light years across. 1034 00:56:52,876 --> 00:56:55,143 But it's relatively thin, 1035 00:56:55,145 --> 00:56:57,512 only about 1,000 light years thick. 1036 00:56:57,514 --> 00:57:01,683 And the whole spiral slowly rotates. 1037 00:57:01,685 --> 00:57:04,653 Our solar system is here. 1038 00:57:04,655 --> 00:57:07,555 And here, 26,000 light years from the Earth, 1039 00:57:07,557 --> 00:57:11,893 is the center, which we see in the direction of Sagittarius. 1040 00:57:11,895 --> 00:57:15,597 In this dense center, there are millions of stars, 1041 00:57:15,599 --> 00:57:19,834 and lots and lots of dust and gas. 1042 00:57:19,836 --> 00:57:22,937 So that's the view of our galaxy from the outside, 1043 00:57:22,939 --> 00:57:24,906 thanks to my imaginary technology. 1044 00:57:24,908 --> 00:57:28,343 But since we live inside the Milky Way, 1045 00:57:28,345 --> 00:57:29,744 when we look towards the center, 1046 00:57:29,746 --> 00:57:33,515 we're looking through much of our own galaxy, 1047 00:57:33,517 --> 00:57:35,550 which means it appears to us 1048 00:57:35,552 --> 00:57:42,157 as a band of stars and dust across the sky-- a milky way. 1049 00:57:42,159 --> 00:57:44,859 ♪ ♪ 1050 00:57:44,861 --> 00:57:47,929 Deep inside this band of stars and dust, 1051 00:57:47,931 --> 00:57:51,966 could a supermassive black hole be lurking? 1052 00:57:51,968 --> 00:57:54,869 GHEZ: The data that we're getting now... 1053 00:57:54,871 --> 00:58:00,308 LEVIN: In the 1990s, astronomers grow determined to solve the mystery, 1054 00:58:00,310 --> 00:58:03,144 to peer through the murky Milky Way 1055 00:58:03,146 --> 00:58:06,881 and learn what, if anything, is at its center. 1056 00:58:06,883 --> 00:58:10,218 One of them is Andrea Ghez. 1057 00:58:10,220 --> 00:58:11,619 GHEZ: One in 20... 1058 00:58:11,621 --> 00:58:14,489 LEVIN: Ghez takes on a daunting challenge. 1059 00:58:14,491 --> 00:58:17,225 She will try to track individual stars 1060 00:58:17,227 --> 00:58:19,961 orbiting the center of the galaxy. 1061 00:58:19,963 --> 00:58:22,530 GHEZ: The essence of this experiment comes from watching 1062 00:58:22,532 --> 00:58:25,400 stars orbit the center of the galaxy. 1063 00:58:25,402 --> 00:58:28,303 So you want to find the stars 1064 00:58:28,305 --> 00:58:32,774 that are as close to the center of the galaxy as possible. 1065 00:58:32,776 --> 00:58:34,676 Which means that I want to get access 1066 00:58:34,678 --> 00:58:38,713 to the largest telescope I can possibly get my hands on. 1067 00:58:40,117 --> 00:58:43,718 LEVIN: And that means coming... here. 1068 00:58:43,720 --> 00:58:45,987 ♪ ♪ 1069 00:58:45,989 --> 00:58:49,557 The summit of Mauna Kea, a dormant volcano 1070 00:58:49,559 --> 00:58:53,128 almost 14,000 feet above the beaches of Hawaii. 1071 00:58:53,130 --> 00:58:56,364 High altitude and low humidity 1072 00:58:56,366 --> 00:59:00,135 make this the ideal place for astronomy. 1073 00:59:00,137 --> 00:59:02,537 ♪ ♪ 1074 00:59:02,539 --> 00:59:07,408 The instrument Ghez uses is Mauna Kea's Keck Observatory, 1075 00:59:07,410 --> 00:59:09,310 one of the largest in the world. 1076 00:59:09,312 --> 00:59:13,915 But despite its size, Keck has the same problem 1077 00:59:13,917 --> 00:59:16,217 as all telescopes on Earth: 1078 00:59:16,219 --> 00:59:20,188 atmospheric distortion. 1079 00:59:20,190 --> 00:59:22,290 GHEZ: Think about looking at a pebble 1080 00:59:22,292 --> 00:59:23,958 at the bottom of a river. 1081 00:59:23,960 --> 00:59:26,261 The river is moving very quickly 1082 00:59:26,263 --> 00:59:29,631 and your view of that pebble is distorted. 1083 00:59:29,633 --> 00:59:31,966 LEVIN: Like a river, 1084 00:59:31,968 --> 00:59:34,302 the Earth's atmosphere is constantly changing, 1085 00:59:34,304 --> 00:59:37,806 bending light like a funhouse mirror. 1086 00:59:37,808 --> 00:59:42,143 To compensate for this, Keck pioneers the scientific use 1087 00:59:42,145 --> 00:59:45,547 of a declassified military technology 1088 00:59:45,549 --> 00:59:47,215 called adaptive optics. 1089 00:59:47,217 --> 00:59:51,719 First, they shine a laser into the sky, 1090 00:59:51,721 --> 00:59:55,056 creating an artificial guide star. 1091 00:59:55,058 --> 00:59:59,227 The turbulent atmosphere distorts the guide star, 1092 00:59:59,229 --> 01:00:02,697 but the computer knows what it should look like, 1093 01:00:02,699 --> 01:00:06,301 and adjusts the telescope mirror accordingly. 1094 01:00:06,303 --> 01:00:09,137 GHEZ: So if you look at yourself in a circus funhouse mirror, 1095 01:00:09,139 --> 01:00:10,638 you look completely distorted. 1096 01:00:10,640 --> 01:00:12,974 And the goal of the adaptive optics system 1097 01:00:12,976 --> 01:00:16,044 is to introduce a second mirror that's the exact opposite shape 1098 01:00:16,046 --> 01:00:17,846 and make you look flat again. 1099 01:00:19,449 --> 01:00:21,182 LEVIN: Buried deep inside the telescope, 1100 01:00:21,184 --> 01:00:23,484 the deformable mirror changes shape 1101 01:00:23,486 --> 01:00:25,620 up to 2,000 times a second 1102 01:00:25,622 --> 01:00:28,790 to reverse the atmosphere's distortion. 1103 01:00:28,792 --> 01:00:32,627 GHEZ: And it has allowed us to take the sharpest images 1104 01:00:32,629 --> 01:00:37,065 ever obtained of the center of the galaxy. 1105 01:00:37,067 --> 01:00:40,935 LEVIN: The sharpness of those images allows Ghez 1106 01:00:40,937 --> 01:00:44,105 to make out individual stars near the center-- 1107 01:00:44,107 --> 01:00:46,774 a huge advance in astronomy. 1108 01:00:46,776 --> 01:00:50,278 She begins recording their positions in 1995. 1109 01:00:50,280 --> 01:00:52,747 GHEZ: And every year since then, 1110 01:00:52,749 --> 01:00:54,983 we've taken an image-- just take a picture. 1111 01:00:54,985 --> 01:00:57,852 LEVIN: Putting those annual snapshots together 1112 01:00:57,854 --> 01:01:01,055 creates a time-lapse movie of stellar orbits. 1113 01:01:01,057 --> 01:01:06,361 And what those movies reveal is astounding. 1114 01:01:06,363 --> 01:01:07,996 ♪ ♪ 1115 01:01:07,998 --> 01:01:10,665 The stars are whipping around the center of the Milky Way 1116 01:01:10,667 --> 01:01:14,836 at phenomenal speeds. 1117 01:01:14,838 --> 01:01:17,205 These things are moving at several thousand, 1118 01:01:17,207 --> 01:01:19,274 up to 10,000 kilometers, per second, 1119 01:01:19,276 --> 01:01:22,377 or ten million miles per hour. 1120 01:01:22,379 --> 01:01:24,178 They're, they're really hauling. 1121 01:01:24,180 --> 01:01:28,416 LEVIN: To go that fast, the stars must be orbiting 1122 01:01:28,418 --> 01:01:31,920 something extremely massive. 1123 01:01:31,922 --> 01:01:33,187 GHEZ: The mass that we infer 1124 01:01:33,189 --> 01:01:36,024 is four million times the mass of the sun. 1125 01:01:36,026 --> 01:01:40,361 What could be four million times the mass of the sun 1126 01:01:40,363 --> 01:01:43,464 yet be completely invisible? 1127 01:01:43,466 --> 01:01:45,333 That is the proof of a black hole. 1128 01:01:45,335 --> 01:01:48,503 LEVIN: And not just any black hole-- 1129 01:01:48,505 --> 01:01:51,506 a supermassive, silent and sleeping, 1130 01:01:51,508 --> 01:01:56,077 right in the center of our own galaxy. 1131 01:01:56,079 --> 01:01:57,779 In fact, this is the best evidence to date 1132 01:01:57,781 --> 01:02:00,815 that we have for the existence of supermassive black holes, 1133 01:02:00,817 --> 01:02:02,817 not only in the center of our own galaxy, 1134 01:02:02,819 --> 01:02:05,153 but anywhere in the universe. 1135 01:02:05,155 --> 01:02:08,022 ♪ ♪ 1136 01:02:08,024 --> 01:02:10,959 A supermassive black hole 1137 01:02:10,961 --> 01:02:13,294 four million times the mass of the sun, 1138 01:02:13,296 --> 01:02:16,898 in the very center of our own Milky Way galaxy. 1139 01:02:16,900 --> 01:02:21,903 From a cosmic perspective, it's right next door. 1140 01:02:21,905 --> 01:02:25,006 And it raises a profound question. 1141 01:02:25,008 --> 01:02:27,775 There are billions of galaxies out there. 1142 01:02:27,777 --> 01:02:30,778 If ours has a supermassive black hole at its center, 1143 01:02:30,780 --> 01:02:33,648 and if quasars are found at the centers 1144 01:02:33,650 --> 01:02:35,116 of their galaxies, 1145 01:02:35,118 --> 01:02:37,652 what about the others? 1146 01:02:37,654 --> 01:02:40,521 ♪ ♪ 1147 01:02:40,523 --> 01:02:43,624 Are there black holes at the centers of galaxies? 1148 01:02:43,626 --> 01:02:45,860 If they are, how common are they? 1149 01:02:45,862 --> 01:02:47,395 We simply didn't know. 1150 01:02:47,397 --> 01:02:51,566 LEVIN: Could astronomers ever hope to find what lurks 1151 01:02:51,568 --> 01:02:53,935 at the centers of other galaxies, 1152 01:02:53,937 --> 01:02:58,806 millions of light years away, as Ghez did in our Milky Way? 1153 01:02:58,808 --> 01:03:00,308 (engine ignites loudly) 1154 01:03:00,310 --> 01:03:03,111 It would take another innovation in astronomy 1155 01:03:03,113 --> 01:03:04,846 to make that possible. 1156 01:03:04,848 --> 01:03:07,081 ANNOUNCER: And lift-off of the space shuttle Discovery, 1157 01:03:07,083 --> 01:03:11,219 with the Hubble Space Telescope, our window on the universe. 1158 01:03:11,221 --> 01:03:15,423 LEVIN: When the Hubble Space Telescope starts delivering clear images 1159 01:03:15,425 --> 01:03:16,591 of distant galaxies, 1160 01:03:16,593 --> 01:03:19,861 a team of astronomers gets to work. 1161 01:03:19,863 --> 01:03:22,897 They become known as "the Nukers" 1162 01:03:22,899 --> 01:03:25,566 because their focus is galactic nuclei, 1163 01:03:25,568 --> 01:03:28,069 the centers of galaxies. 1164 01:03:28,071 --> 01:03:31,105 One of them is Tod Lauer. 1165 01:03:31,107 --> 01:03:34,475 Step one, we take a picture of the galaxy 1166 01:03:34,477 --> 01:03:36,277 with the Hubble Space Telescope. 1167 01:03:36,279 --> 01:03:39,514 It shows us where the stars in the galaxy are. 1168 01:03:39,516 --> 01:03:42,850 It tells us its structure in exquisite resolution. 1169 01:03:42,852 --> 01:03:45,053 ♪ ♪ 1170 01:03:45,055 --> 01:03:47,889 LEVIN: The key to finding supermassive black holes 1171 01:03:47,891 --> 01:03:51,859 is to learn how fast the stars in the galaxy are moving. 1172 01:03:51,861 --> 01:03:56,130 Galaxies outside our own are much too far away 1173 01:03:56,132 --> 01:03:59,500 to measure the speed of individual stars. 1174 01:03:59,502 --> 01:04:02,537 But by analyzing the way light is shifted from blue to red 1175 01:04:02,539 --> 01:04:05,573 at different points in the galaxy, 1176 01:04:05,575 --> 01:04:08,876 astronomers can put together an average speed of stars 1177 01:04:08,878 --> 01:04:12,080 orbiting the center. 1178 01:04:12,082 --> 01:04:16,651 It's accurate enough to create a replica in a computer. 1179 01:04:16,653 --> 01:04:19,320 The second step, where the real work begins, 1180 01:04:19,322 --> 01:04:23,024 is to try to model the observations. 1181 01:04:23,026 --> 01:04:26,861 And we actually do that by building models of galaxies 1182 01:04:26,863 --> 01:04:28,229 in the computer. 1183 01:04:28,231 --> 01:04:31,399 LEVIN: It's known as Schwarzschild's method, 1184 01:04:31,401 --> 01:04:35,002 developed by Princeton astronomer Martin Schwarzschild, 1185 01:04:35,004 --> 01:04:36,904 son of Karl Schwarzschild, 1186 01:04:36,906 --> 01:04:39,107 whose mathematics first described 1187 01:04:39,109 --> 01:04:42,643 the possibility of black holes. 1188 01:04:42,645 --> 01:04:44,912 LAUER: Martin Schwarzschild's trick was, 1189 01:04:44,914 --> 01:04:48,883 he would actually build up a model of the galaxy 1190 01:04:48,885 --> 01:04:51,953 that not only had where the mass was, 1191 01:04:51,955 --> 01:04:54,789 but it also had how the stars were moving. 1192 01:04:54,791 --> 01:04:56,057 ♪ ♪ 1193 01:04:56,059 --> 01:04:57,525 LEVIN: For each galaxy they investigate, 1194 01:04:57,527 --> 01:05:01,996 the Nukers painstakingly build a computer model and then, 1195 01:05:01,998 --> 01:05:03,397 using trial and error, 1196 01:05:03,399 --> 01:05:06,601 adjust the parameters of mass and velocity-- 1197 01:05:06,603 --> 01:05:10,004 trying to make the model match the original observations 1198 01:05:10,006 --> 01:05:12,940 they got from the Hubble. 1199 01:05:12,942 --> 01:05:15,243 LAUER: And we say, "Let's try a star here, 1200 01:05:15,245 --> 01:05:16,377 "let's try one over here. 1201 01:05:16,379 --> 01:05:18,212 "Let's have it go around this way. 1202 01:05:18,214 --> 01:05:19,780 Let's have this one go around that way." 1203 01:05:19,782 --> 01:05:23,317 And we do this thousands and thousands of times 1204 01:05:23,319 --> 01:05:24,919 until we build up a library 1205 01:05:24,921 --> 01:05:28,990 of how stars can orbit in this galaxy. 1206 01:05:30,460 --> 01:05:33,528 Success is when observations of the model 1207 01:05:33,530 --> 01:05:38,866 match the observations taken with the Hubble Space Telescope. 1208 01:05:38,868 --> 01:05:42,203 LEVIN: But that doesn't happen. 1209 01:05:42,205 --> 01:05:45,139 The models are missing something. 1210 01:05:45,141 --> 01:05:47,575 We try it again and again and again, 1211 01:05:47,577 --> 01:05:49,977 all with no black hole yet, and we say, 1212 01:05:49,979 --> 01:05:54,148 "Gee, we really can't get the observations explained 1213 01:05:54,150 --> 01:05:55,650 by the model." 1214 01:05:55,652 --> 01:05:59,620 LEVIN: Only when they add an enormous invisible mass 1215 01:05:59,622 --> 01:06:01,622 at the galaxy's center 1216 01:06:01,624 --> 01:06:05,459 does the model match the Hubble observations. 1217 01:06:05,461 --> 01:06:08,663 LAUER: Almost always we have to put in 1218 01:06:08,665 --> 01:06:10,264 a black hole at the center. 1219 01:06:10,266 --> 01:06:12,033 We can't match the observations 1220 01:06:12,035 --> 01:06:16,504 without a black hole in the model. 1221 01:06:16,506 --> 01:06:18,206 ♪ ♪ 1222 01:06:18,208 --> 01:06:21,375 LEVIN: Of roughly three dozen galaxies that the Nukers investigate, 1223 01:06:21,377 --> 01:06:25,580 virtually all of them require a supermassive black hole. 1224 01:06:25,582 --> 01:06:29,417 And since then, other observations have made us 1225 01:06:29,419 --> 01:06:30,918 even more certain 1226 01:06:30,920 --> 01:06:35,489 that supermassives and galaxies go together. 1227 01:06:35,491 --> 01:06:37,124 Every galaxy we've looked for one, 1228 01:06:37,126 --> 01:06:39,961 we have found a supermassive black hole in its center. 1229 01:06:41,531 --> 01:06:43,931 LEVIN: It's a stunning revelation. 1230 01:06:43,933 --> 01:06:45,399 Supermassives-- 1231 01:06:45,401 --> 01:06:49,303 once an entirely unexpected category of black holes-- 1232 01:06:49,305 --> 01:06:51,072 may be common, 1233 01:06:51,074 --> 01:06:53,941 not only at the center of our galaxy, 1234 01:06:53,943 --> 01:06:56,510 but of all galaxies. 1235 01:06:56,512 --> 01:06:59,013 Take galaxy M31, 1236 01:06:59,015 --> 01:07:02,250 also known as the Great Andromeda Galaxy. 1237 01:07:02,252 --> 01:07:05,820 It's two-and-a-half million light years away. 1238 01:07:05,822 --> 01:07:10,024 On a clear night, you can see it from Earth. 1239 01:07:10,026 --> 01:07:12,660 But even with the Hubble Space Telescope, 1240 01:07:12,662 --> 01:07:16,831 we can't make out precise details of its center. 1241 01:07:16,833 --> 01:07:18,532 Still, we're pretty sure 1242 01:07:18,534 --> 01:07:22,203 there's something extremely massive hiding there. 1243 01:07:22,205 --> 01:07:25,139 ♪ ♪ 1244 01:07:25,141 --> 01:07:28,376 What if we could take a closer look? 1245 01:07:28,378 --> 01:07:32,280 What if we could visit a galaxy far, far away? 1246 01:07:32,282 --> 01:07:36,917 ♪ ♪ 1247 01:07:41,324 --> 01:07:43,624 As we enter the outer part of Andromeda, 1248 01:07:43,626 --> 01:07:47,928 we're still too far away to see what's lurking at the center. 1249 01:07:47,930 --> 01:07:48,996 But we can make out 1250 01:07:48,998 --> 01:07:52,199 a dense cluster of stars in the core, 1251 01:07:52,201 --> 01:07:53,701 and that could be a sign 1252 01:07:53,703 --> 01:07:57,104 that there's a giant black hole nearby. 1253 01:07:57,106 --> 01:07:58,506 ♪ ♪ 1254 01:07:58,508 --> 01:08:01,709 Billions of years ago, it would have been surrounded 1255 01:08:01,711 --> 01:08:06,414 by gas and stars and other small black holes. 1256 01:08:06,416 --> 01:08:08,749 The black hole may have powered a quasar, 1257 01:08:08,751 --> 01:08:13,487 feeding mad, and blasting out blinding radiation. 1258 01:08:13,489 --> 01:08:15,623 Over hundreds of millions of years, 1259 01:08:15,625 --> 01:08:16,891 it would have consumed 1260 01:08:16,893 --> 01:08:20,628 all the available gas and the closest stars. 1261 01:08:20,630 --> 01:08:23,698 ♪ ♪ 1262 01:08:23,700 --> 01:08:27,368 (screen beeping) 1263 01:08:27,370 --> 01:08:33,307 ♪ ♪ 1264 01:08:33,309 --> 01:08:35,976 These days it's relatively quiet. 1265 01:08:35,978 --> 01:08:38,379 But it has some distinctive features 1266 01:08:38,381 --> 01:08:41,415 we've never seen before. 1267 01:08:41,417 --> 01:08:43,484 First, it's colossal. 1268 01:08:43,486 --> 01:08:47,054 If it were dropped in our solar system, 1269 01:08:47,056 --> 01:08:49,623 Mercury, Venus, Earth, and Mars 1270 01:08:49,625 --> 01:08:53,494 would all be trapped inside the event horizon. 1271 01:08:53,496 --> 01:08:57,765 That's big, but it's nothing compared to the sheer mass: 1272 01:08:57,767 --> 01:09:01,068 100 million times the mass of the sun. 1273 01:09:01,070 --> 01:09:03,904 And the destruction won't end there. 1274 01:09:03,906 --> 01:09:06,207 Jupiter won't last long. 1275 01:09:06,209 --> 01:09:08,142 The gravitational field of the supermassive 1276 01:09:08,144 --> 01:09:12,046 will grab hold and swallow it whole. 1277 01:09:12,048 --> 01:09:16,050 Eventually, Saturn will suffer the same fate. 1278 01:09:16,052 --> 01:09:21,856 The outer planets might survive, but in cold and dark orbits. 1279 01:09:21,858 --> 01:09:24,658 ♪ ♪ 1280 01:09:24,660 --> 01:09:26,861 This black hole rotates rapidly, 1281 01:09:26,863 --> 01:09:30,131 distorting and dragging the fabric of space-time. 1282 01:09:30,133 --> 01:09:32,466 Like all black holes, 1283 01:09:32,468 --> 01:09:36,270 the event horizon is completely featureless. 1284 01:09:36,272 --> 01:09:38,973 Remember, there's nothing there. 1285 01:09:38,975 --> 01:09:42,410 It's just a boundary that conceals the interior. 1286 01:09:42,412 --> 01:09:45,479 But the accretion disk can tell us a lot 1287 01:09:45,481 --> 01:09:46,947 about what's going on. 1288 01:09:46,949 --> 01:09:53,187 That's the fiery ring of gas and dust around the black hole. 1289 01:09:53,189 --> 01:09:56,056 ♪ ♪ 1290 01:09:56,058 --> 01:10:00,394 Imagine if we could release a swarm of autonomous robots 1291 01:10:00,396 --> 01:10:02,663 to explore the accretion disk. 1292 01:10:02,665 --> 01:10:04,465 ♪ ♪ 1293 01:10:04,467 --> 01:10:06,867 The disk is spinning at an incredible speed-- 1294 01:10:06,869 --> 01:10:09,603 as much as half the speed of light. 1295 01:10:09,605 --> 01:10:11,672 If Jupiter moved that fast, 1296 01:10:11,674 --> 01:10:16,544 it would complete its entire orbit in a few hours. 1297 01:10:16,546 --> 01:10:19,613 The region around the black hole is a cosmic tornado. 1298 01:10:21,250 --> 01:10:24,418 Now our swarm is caught in the whirlwind, too. 1299 01:10:24,420 --> 01:10:27,855 They're like tracers dropped into the storm 1300 01:10:27,857 --> 01:10:30,958 to map the movement. 1301 01:10:30,960 --> 01:10:33,494 The middle robot can send us images. 1302 01:10:33,496 --> 01:10:35,696 It's following the leader like a race car 1303 01:10:35,698 --> 01:10:38,466 speeding around the track. 1304 01:10:38,468 --> 01:10:41,235 From here, the extreme warping of space-time 1305 01:10:41,237 --> 01:10:42,403 around the black hole 1306 01:10:42,405 --> 01:10:44,805 plays crazy tricks on our eyes. 1307 01:10:44,807 --> 01:10:48,242 It looks like there's one accretion disk 1308 01:10:48,244 --> 01:10:49,977 whipping around the equator, 1309 01:10:49,979 --> 01:10:54,482 and another arcing over and under the poles. 1310 01:10:56,586 --> 01:10:58,886 But that's an illusion. 1311 01:10:58,888 --> 01:11:02,156 The black hole's extreme gravity bends the path of light 1312 01:11:02,158 --> 01:11:04,458 emitted behind the black hole, 1313 01:11:04,460 --> 01:11:07,027 and makes it look like the accretion disk 1314 01:11:07,029 --> 01:11:09,597 is both above and below. 1315 01:11:09,599 --> 01:11:12,066 There's actually nothing around the poles. 1316 01:11:12,068 --> 01:11:14,502 It's just the passing light rays. 1317 01:11:14,504 --> 01:11:17,738 That's gravitational lensing again. 1318 01:11:17,740 --> 01:11:20,875 Drawing much closer to the event horizon, 1319 01:11:20,877 --> 01:11:23,777 the gravitational lensing would become so extreme 1320 01:11:23,779 --> 01:11:27,548 that one of my robots could look straight ahead 1321 01:11:27,550 --> 01:11:30,417 and eventually see its own back, 1322 01:11:30,419 --> 01:11:35,689 the light forever trapped in an eternal circle. 1323 01:11:35,691 --> 01:11:38,792 So that's our tour of the supermassive black hole 1324 01:11:38,794 --> 01:11:41,295 at the center of the Andromeda Galaxy. 1325 01:11:41,297 --> 01:11:42,496 Pretty amazing. 1326 01:11:42,498 --> 01:11:46,000 Also amazing: nothing in the mathematics 1327 01:11:46,002 --> 01:11:52,039 led scientists to imagine that black holes could get that big. 1328 01:11:52,041 --> 01:11:56,477 ♪ ♪ 1329 01:11:59,048 --> 01:12:00,314 As strange as they are, 1330 01:12:00,316 --> 01:12:02,516 ordinary stellar-mass black holes 1331 01:12:02,518 --> 01:12:05,052 were at least predicted by theory. 1332 01:12:05,054 --> 01:12:08,556 Supermassives are a complete surprise. 1333 01:12:08,558 --> 01:12:12,159 ♪ ♪ 1334 01:12:12,161 --> 01:12:13,928 For the stellar-mass black holes, 1335 01:12:13,930 --> 01:12:17,298 people thought about them from a theoretical perspective. 1336 01:12:17,300 --> 01:12:19,867 And then we found them observationally. 1337 01:12:19,869 --> 01:12:23,170 The supermassive black holes, the story has been inverted. 1338 01:12:23,172 --> 01:12:27,474 We actually found evidence of them observationally first. 1339 01:12:27,476 --> 01:12:29,243 And now we're working on the theory 1340 01:12:29,245 --> 01:12:31,378 of, how did these things come into being? 1341 01:12:31,380 --> 01:12:33,414 ♪ ♪ 1342 01:12:33,416 --> 01:12:35,182 LEVIN: We already know that stars can collapse 1343 01:12:35,184 --> 01:12:37,418 to create ordinary black holes. 1344 01:12:37,420 --> 01:12:42,022 But supermassives are bigger by many orders of magnitude. 1345 01:12:42,024 --> 01:12:46,293 Cygnus X-1 is 15 times as big as our sun. 1346 01:12:46,295 --> 01:12:49,530 The supermassive at the center of our Milky Way 1347 01:12:49,532 --> 01:12:52,933 is four million times as big as our sun. 1348 01:12:52,935 --> 01:12:54,468 The one in the Andromeda galaxy 1349 01:12:54,470 --> 01:12:58,105 is 100 million times as big as our sun. 1350 01:12:58,107 --> 01:13:01,141 And it's not the biggest-- not even close. 1351 01:13:01,143 --> 01:13:05,679 There are supermassives ten, even 20 billion times 1352 01:13:05,681 --> 01:13:10,150 the mass of our sun. 1353 01:13:10,152 --> 01:13:15,122 How is it possible to make such gigantic black holes? 1354 01:13:15,124 --> 01:13:20,160 Could supermassives have come from collapsed stars? 1355 01:13:20,162 --> 01:13:24,031 That seems very unlikely-- we don't know any stars 1356 01:13:24,033 --> 01:13:27,401 billions of times bigger than the sun. 1357 01:13:27,403 --> 01:13:30,638 TYSON: We know about black holes you might get from a dying star. 1358 01:13:30,640 --> 01:13:33,607 They have several times the mass of the sun 1359 01:13:33,609 --> 01:13:35,676 contained within them. 1360 01:13:35,678 --> 01:13:39,313 But millions of times the mass of the sun. 1361 01:13:39,315 --> 01:13:43,384 If that's the case, a dying star cannot have possibly made it. 1362 01:13:45,187 --> 01:13:48,355 LEVIN: So do these supermassives-- 1363 01:13:48,357 --> 01:13:51,425 millions or even billions of times heavier than the sun-- 1364 01:13:51,427 --> 01:13:57,031 somehow just grow, packing it on like voracious giants? 1365 01:13:57,033 --> 01:13:59,933 The wild thing about black holes is that they feed. 1366 01:13:59,935 --> 01:14:04,271 They're constantly devouring anything that comes 1367 01:14:04,273 --> 01:14:06,507 within their sphere of influence, 1368 01:14:06,509 --> 01:14:07,741 so they grow. 1369 01:14:07,743 --> 01:14:12,346 LEVIN: But how exactly do they grow? 1370 01:14:12,348 --> 01:14:15,082 What do they eat, and where do they find it? 1371 01:14:16,886 --> 01:14:18,686 NATARAJAN: We believe that black holes grow 1372 01:14:18,688 --> 01:14:20,187 by accretion of gas. 1373 01:14:20,189 --> 01:14:24,291 And the way this works is that you have a lot of gas around 1374 01:14:24,293 --> 01:14:26,060 in the center of a galaxy, 1375 01:14:26,062 --> 01:14:30,130 and this gas would then assemble and form an accretion disk. 1376 01:14:31,434 --> 01:14:34,902 LEVIN: The accretion disk is made up of hydrogen, helium, 1377 01:14:34,904 --> 01:14:38,238 and other elements in a gaseous form. 1378 01:14:38,240 --> 01:14:40,140 The immense gravity of the black hole 1379 01:14:40,142 --> 01:14:43,110 pulls the gas in toward it. 1380 01:14:43,112 --> 01:14:44,445 As it swirls around, 1381 01:14:44,447 --> 01:14:47,748 it orbits closer and closer to the black hole, 1382 01:14:47,750 --> 01:14:49,683 and the feeding begins. 1383 01:14:49,685 --> 01:14:53,520 NATARAJAN: The stuff in the inner regions would get slowly pulled in, 1384 01:14:53,522 --> 01:14:56,490 sped up, will reach the event horizon, 1385 01:14:56,492 --> 01:14:58,225 and then that's it. 1386 01:14:58,227 --> 01:15:04,164 LEVIN: Whatever gas crosses the event horizon disappears forever. 1387 01:15:04,166 --> 01:15:08,836 The black hole has absorbed that material. 1388 01:15:08,838 --> 01:15:12,906 So it actually adds to the mass of the black hole. 1389 01:15:14,577 --> 01:15:17,144 LEVIN: So this is one way a black hole can grow: 1390 01:15:17,146 --> 01:15:20,781 gradually nibbling gas and dust. 1391 01:15:20,783 --> 01:15:24,084 But it's not the only way. 1392 01:15:24,086 --> 01:15:27,821 Cygnus X-1 has been slowly stripping material 1393 01:15:27,823 --> 01:15:29,189 off a nearby star-- 1394 01:15:29,191 --> 01:15:31,825 a process that will likely go on 1395 01:15:31,827 --> 01:15:35,696 for thousands or millions of years. 1396 01:15:35,698 --> 01:15:40,334 But what if a black hole could rip an entire star apart 1397 01:15:40,336 --> 01:15:43,971 in just a matter of years, or even weeks? 1398 01:15:43,973 --> 01:15:46,774 That would be a very violent event. 1399 01:15:46,776 --> 01:15:51,879 And a team of space explorers is on the lookout. 1400 01:15:51,881 --> 01:15:56,583 This is the Operations Control Center for a space telescope... 1401 01:15:56,585 --> 01:15:57,651 I have you five-by-five... 1402 01:15:57,653 --> 01:16:00,120 We show beginning of track at 0330. 1403 01:16:00,122 --> 01:16:02,823 LEVIN: ...the Chandra X-Ray Observatory. 1404 01:16:02,825 --> 01:16:08,262 (people talking on radio) 1405 01:16:08,264 --> 01:16:11,732 LEVIN: Orbiting up to 86,000 miles above the Earth, 1406 01:16:11,734 --> 01:16:14,101 Chandra takes high-resolution images 1407 01:16:14,103 --> 01:16:17,571 of objects that emit X-rays. 1408 01:16:19,408 --> 01:16:24,311 This is one: a short-lived, extremely violent event 1409 01:16:24,313 --> 01:16:26,079 called a transient, 1410 01:16:26,081 --> 01:16:29,516 which fascinates James Guillochon. 1411 01:16:29,518 --> 01:16:35,088 GUILLOCHON: Supernovae, the destruction of planets by their host stars. 1412 01:16:35,090 --> 01:16:40,527 Yeah, I'm just fascinated with destroying things for science. 1413 01:16:40,529 --> 01:16:44,097 LEVIN: James is investigating a mystery discovered by a colleague, 1414 01:16:44,099 --> 01:16:45,199 Dacheng Lin. 1415 01:16:45,201 --> 01:16:47,367 This blur on James's screen 1416 01:16:47,369 --> 01:16:51,271 is actually a massive sudden burst of X-ray energy, 1417 01:16:51,273 --> 01:16:54,007 caught by accident. 1418 01:16:54,009 --> 01:16:56,944 GUILLOCHON: This little smudge popped up in the background of this image. 1419 01:16:56,946 --> 01:16:58,612 And given its great distance, 1420 01:16:58,614 --> 01:17:00,681 it's actually tremendously bright. 1421 01:17:02,685 --> 01:17:06,420 LEVIN: Could it be a black hole caught in the act of being born 1422 01:17:06,422 --> 01:17:12,359 in the violent collapse of a huge star, a supernova? 1423 01:17:12,361 --> 01:17:14,595 (explosion roars) 1424 01:17:14,597 --> 01:17:15,929 Perhaps. 1425 01:17:15,931 --> 01:17:19,199 But the intense radiation released by supernova 1426 01:17:19,201 --> 01:17:21,969 would only linger for a few months. 1427 01:17:21,971 --> 01:17:24,104 ♪ ♪ 1428 01:17:24,106 --> 01:17:29,276 So how long has this mystery object been blasting out X-rays? 1429 01:17:29,278 --> 01:17:33,647 To find out, they look at images of that same part of the sky 1430 01:17:33,649 --> 01:17:35,649 taken at earlier dates. 1431 01:17:35,651 --> 01:17:38,218 2015. 1432 01:17:38,220 --> 01:17:40,520 2011. 1433 01:17:40,522 --> 01:17:43,056 2008. 1434 01:17:43,058 --> 01:17:46,226 2005, July. 1435 01:17:46,228 --> 01:17:49,963 2005, April. 1436 01:17:49,965 --> 01:17:53,467 No X-rays detected. 1437 01:17:53,469 --> 01:17:57,604 But the X-rays are there just three months later, in July. 1438 01:17:57,606 --> 01:18:00,841 And the powerful, bright signal has continued 1439 01:18:00,843 --> 01:18:03,477 for more than ten years, 1440 01:18:03,479 --> 01:18:06,413 from July 2005 to the present, 1441 01:18:06,415 --> 01:18:09,616 far too long to be a supernova. 1442 01:18:09,618 --> 01:18:11,752 So what could it be? 1443 01:18:14,924 --> 01:18:19,660 A black hole that's not feeding is quiet and completely dark. 1444 01:18:19,662 --> 01:18:22,296 It won't show up on any telescope. 1445 01:18:22,298 --> 01:18:25,866 But a black hole that is feeding is different. 1446 01:18:25,868 --> 01:18:29,536 When it feeds, it blasts out X-rays. 1447 01:18:29,538 --> 01:18:32,272 So could this be a black hole 1448 01:18:32,274 --> 01:18:36,043 that's suddenly begun devouring something big? 1449 01:18:36,045 --> 01:18:41,114 TYSON: What effect will this have on anything that comes near? 1450 01:18:41,116 --> 01:18:44,885 What would it do to a star that wanders too close? 1451 01:18:44,887 --> 01:18:50,257 Well, it will flay a star layer by layer, 1452 01:18:50,259 --> 01:18:53,493 ultimately devouring 1453 01:18:53,495 --> 01:18:55,262 the entire star. 1454 01:18:55,264 --> 01:18:57,531 ♪ ♪ 1455 01:18:57,533 --> 01:19:01,068 LEVIN: Unlike Cygnus X-1, this is no mere nibbling. 1456 01:19:01,070 --> 01:19:04,171 This is a ten-year feeding frenzy, 1457 01:19:04,173 --> 01:19:07,441 a massive black hole devouring an entire star 1458 01:19:07,443 --> 01:19:12,446 in a cosmic blink of an eye. 1459 01:19:12,448 --> 01:19:15,649 It's the result of a chance collision-- 1460 01:19:15,651 --> 01:19:18,618 when an unlucky star wanders too close, 1461 01:19:18,620 --> 01:19:23,423 and the black hole's extreme gravity actually rips it apart. 1462 01:19:23,425 --> 01:19:25,158 GUILLOCHON: The gravity from the black hole 1463 01:19:25,160 --> 01:19:27,127 will progressively get stronger and stronger 1464 01:19:27,129 --> 01:19:28,495 as the star gets near. 1465 01:19:28,497 --> 01:19:31,698 And at that point, the star will begin to deform. 1466 01:19:33,402 --> 01:19:36,703 LEVIN: It's called tidal disruption. 1467 01:19:38,407 --> 01:19:40,107 It's similar to the way our moon's gravity 1468 01:19:40,109 --> 01:19:44,177 easily moves all the world's oceans. 1469 01:19:44,179 --> 01:19:46,213 The tides caused by a black hole 1470 01:19:46,215 --> 01:19:48,782 would be billions of times stronger 1471 01:19:48,784 --> 01:19:53,320 and much more violent. 1472 01:19:53,322 --> 01:19:55,856 where a star could be ripped apart by the black hole. 1473 01:19:55,858 --> 01:19:58,325 So you would see sort of a plume of light 1474 01:19:58,327 --> 01:20:03,730 from the last gasp of the material in the star. 1475 01:20:03,732 --> 01:20:06,833 LEVIN: But there is a chance for some part of the star to escape, 1476 01:20:06,835 --> 01:20:11,138 as James illustrates. 1477 01:20:11,140 --> 01:20:14,007 As the star is elongated by the black hole's tidal forces, 1478 01:20:14,009 --> 01:20:18,045 it will essentially be feeding the black hole 1479 01:20:18,047 --> 01:20:22,749 at the same time as half of it is trying to escape. 1480 01:20:22,751 --> 01:20:25,986 So everything above this point, approximately, 1481 01:20:25,988 --> 01:20:29,222 will have the chance of leaving the galaxy. 1482 01:20:29,224 --> 01:20:31,825 It's moving that rapidly. 1483 01:20:31,827 --> 01:20:34,461 And everything below this point 1484 01:20:34,463 --> 01:20:36,997 will fall back onto the black hole 1485 01:20:36,999 --> 01:20:39,599 and eventually be consumed by it. 1486 01:20:41,170 --> 01:20:44,971 LEVIN: So this is another way for a black hole to gain weight. 1487 01:20:44,973 --> 01:20:48,842 Unlike the slow steady nibbling of Cygnus X-1, 1488 01:20:48,844 --> 01:20:52,412 this black hole is devouring most of an entire star 1489 01:20:52,414 --> 01:20:55,882 in one gulp. 1490 01:20:55,884 --> 01:20:58,318 But whether a black hole feeds suddenly, 1491 01:20:58,320 --> 01:20:59,753 by swallowing half a star, 1492 01:20:59,755 --> 01:21:02,322 or steadily, through accretion, 1493 01:21:02,324 --> 01:21:06,426 astronomers still face a problem when they try to understand 1494 01:21:06,428 --> 01:21:10,030 how supermassives got so big-- 1495 01:21:10,032 --> 01:21:12,566 the timing problem. 1496 01:21:13,836 --> 01:21:17,471 The trouble begins with the very oldest supermassives: 1497 01:21:17,473 --> 01:21:21,775 quasars, those very bright, very distant, 1498 01:21:21,777 --> 01:21:22,976 and ancient objects 1499 01:21:22,978 --> 01:21:28,715 first discovered in the early 1960s. 1500 01:21:28,717 --> 01:21:30,951 The conundrum was when we started finding these quasars, 1501 01:21:30,953 --> 01:21:34,121 very bright quasars, very early on in the universe. 1502 01:21:36,959 --> 01:21:38,892 DALE KOCEVSKI: They're giving off so much energy 1503 01:21:38,894 --> 01:21:40,927 that they have to have very massive supermassive black holes 1504 01:21:40,929 --> 01:21:42,295 at their center. 1505 01:21:42,297 --> 01:21:46,433 LEVIN: But quasars are extremely far away, 1506 01:21:46,435 --> 01:21:49,803 which means that they're part of the very early universe, 1507 01:21:49,805 --> 01:21:53,440 which began nearly 14 billion years ago. 1508 01:21:54,877 --> 01:21:56,042 NATARAJAN: Bright quasars, 1509 01:21:56,044 --> 01:22:00,147 600 million years after the Big Bang. 1510 01:22:00,149 --> 01:22:02,682 A fraction of today's age. 1511 01:22:02,684 --> 01:22:05,785 LEVIN: And, they're enormous. 1512 01:22:05,787 --> 01:22:09,389 NATARAJAN: So billion-solar-mass black holes, these behemoths, 1513 01:22:09,391 --> 01:22:12,292 had to be in place when the universe 1514 01:22:12,294 --> 01:22:15,095 was about 550 million years old. 1515 01:22:15,097 --> 01:22:16,763 Now you have a problem. 1516 01:22:16,765 --> 01:22:19,032 Because you have to grow something really big, 1517 01:22:19,034 --> 01:22:20,400 really fast. 1518 01:22:20,402 --> 01:22:24,237 And you are bumping up against sort of physical limits. 1519 01:22:24,239 --> 01:22:25,605 ♪ ♪ 1520 01:22:25,607 --> 01:22:27,274 LEVIN: Whether a black hole is nibbling 1521 01:22:27,276 --> 01:22:29,142 or gulping down its meal, 1522 01:22:29,144 --> 01:22:32,612 it turns out that accretion-- how black holes feed-- 1523 01:22:32,614 --> 01:22:35,182 has a speed limit. 1524 01:22:35,184 --> 01:22:38,652 Named after English astronomer Arthur Eddington, 1525 01:22:38,654 --> 01:22:42,656 the Eddington Limit will not allow a black hole 1526 01:22:42,658 --> 01:22:44,424 to feed too fast 1527 01:22:44,426 --> 01:22:46,593 because of the light blasting out 1528 01:22:46,595 --> 01:22:48,795 from its own accretion disk. 1529 01:22:48,797 --> 01:22:50,830 ♪ ♪ 1530 01:22:50,832 --> 01:22:53,099 GLIKMAN: Light has a pressure. 1531 01:22:53,101 --> 01:22:56,102 So photons can impart a force on something. 1532 01:22:56,104 --> 01:23:01,341 We see this in winds from stars: Light is pushing out gas. 1533 01:23:03,312 --> 01:23:06,646 So there's a limit to how fast you can feed a black hole 1534 01:23:06,648 --> 01:23:12,118 before its own luminosity quenches its own growth. 1535 01:23:14,489 --> 01:23:18,191 LEVIN: So given this speed limit, how did early supermassives-- 1536 01:23:18,193 --> 01:23:22,862 quasars-- get so big, so fast? 1537 01:23:22,864 --> 01:23:27,067 Could there be a way to bypass the speed limit entirely? 1538 01:23:30,772 --> 01:23:34,774 NATARAJAN: The problem is still time itself. 1539 01:23:34,776 --> 01:23:36,776 How do you grow them 1540 01:23:36,778 --> 01:23:38,578 to a billion times the mass of the sun? 1541 01:23:38,580 --> 01:23:42,215 What are the conditions that you need for that kind of growth? 1542 01:23:43,585 --> 01:23:47,454 LEVIN: Some scientists are now asking: What if there's a way 1543 01:23:47,456 --> 01:23:48,822 to create a black hole 1544 01:23:48,824 --> 01:23:52,125 that's already much more massive from birth, 1545 01:23:52,127 --> 01:23:54,594 giving it a head start? 1546 01:23:54,596 --> 01:23:56,363 NATARAJAN: If there was a physical mechanism 1547 01:23:56,365 --> 01:23:59,332 that would allow you to make a black hole seed 1548 01:23:59,334 --> 01:24:01,334 which was much more massive from the get-go, 1549 01:24:01,336 --> 01:24:03,903 then the timing crunch is not as much of an issue, 1550 01:24:03,905 --> 01:24:06,406 and the growing problem is not as acute. 1551 01:24:08,777 --> 01:24:10,277 LEVIN: The answer, some believe, 1552 01:24:10,279 --> 01:24:13,980 is to create a black hole directly from a cloud of gas: 1553 01:24:13,982 --> 01:24:18,652 a scenario called direct collapse. 1554 01:24:20,455 --> 01:24:23,490 It starts with gas clouds made of hydrogen, helium, 1555 01:24:23,492 --> 01:24:24,824 and other elements-- 1556 01:24:24,826 --> 01:24:29,929 the same raw materials from which stars are born. 1557 01:24:29,931 --> 01:24:31,164 The denser clouds will start to collapse 1558 01:24:31,166 --> 01:24:32,499 under their own gravity. 1559 01:24:32,501 --> 01:24:35,168 And as they collapse, parts that are more dense 1560 01:24:35,170 --> 01:24:36,870 will collapse more quickly. 1561 01:24:36,872 --> 01:24:39,939 And so what happens is, the cloud fragments. 1562 01:24:39,941 --> 01:24:43,076 LEVIN: Those fragments continue collapsing 1563 01:24:43,078 --> 01:24:47,047 until the hydrogen atoms within them begin to merge. 1564 01:24:47,049 --> 01:24:51,951 Nuclear fusion begins, and stars are created. 1565 01:24:51,953 --> 01:24:57,691 But what if a giant gas cloud collapsed without making stars? 1566 01:24:59,528 --> 01:25:01,628 We realized that there are a set of physical conditions 1567 01:25:01,630 --> 01:25:04,998 that would allow you to form a very large gas disk 1568 01:25:05,000 --> 01:25:07,667 prior to the formation of any stars. 1569 01:25:07,669 --> 01:25:11,471 So this gas disk starts getting unstable. 1570 01:25:11,473 --> 01:25:14,207 That would allow the mass to sort of flow into the center 1571 01:25:14,209 --> 01:25:15,975 very, very rapidly 1572 01:25:15,977 --> 01:25:18,378 and make a very massive black hole. 1573 01:25:18,380 --> 01:25:20,647 ♪ ♪ 1574 01:25:20,649 --> 01:25:23,683 LEVIN: It's something we've all seen in nature, 1575 01:25:23,685 --> 01:25:27,153 from tornadoes to bathtubs-- 1576 01:25:27,155 --> 01:25:30,190 a vortex. 1577 01:25:30,192 --> 01:25:33,293 But on a supermassive scale. 1578 01:25:33,295 --> 01:25:36,096 If you're in a bathtub and you pull the plug out 1579 01:25:36,098 --> 01:25:38,098 and you see the water flowing in a vortex, 1580 01:25:38,100 --> 01:25:39,966 very fast down to the center, 1581 01:25:39,968 --> 01:25:42,035 that's exactly what happens. 1582 01:25:43,605 --> 01:25:45,572 LEVIN: Direct collapse might be a way 1583 01:25:45,574 --> 01:25:48,375 to create very large black holes early in the universe 1584 01:25:48,377 --> 01:25:51,544 from enormous gas clouds, 1585 01:25:51,546 --> 01:25:55,715 completely skipping the star stage. 1586 01:25:55,717 --> 01:25:58,218 Because they would be so large already at birth, 1587 01:25:58,220 --> 01:26:00,587 these direct-collapse black holes 1588 01:26:00,589 --> 01:26:04,457 would have a head start, helping them to quickly grow 1589 01:26:04,459 --> 01:26:08,194 into the enormous young supermassives we see 1590 01:26:08,196 --> 01:26:10,730 in the distant universe. 1591 01:26:10,732 --> 01:26:15,301 NATARAJAN: You could potentially have these direct-collapse black holes. 1592 01:26:15,303 --> 01:26:17,370 So black holes whose original masses, 1593 01:26:17,372 --> 01:26:19,739 seed masses, the initial masses, 1594 01:26:19,741 --> 01:26:22,976 are about 10,000 to maybe 100,000 times 1595 01:26:22,978 --> 01:26:24,277 the mass of the sun, 1596 01:26:24,279 --> 01:26:28,348 and that they form from the get-go with that mass. 1597 01:26:28,350 --> 01:26:30,250 ♪ ♪ 1598 01:26:30,252 --> 01:26:34,687 LEVIN: Direct collapse may explain how enormous early supermassives 1599 01:26:34,689 --> 01:26:36,589 got their start. 1600 01:26:36,591 --> 01:26:40,827 But there's another fundamental question about supermassives. 1601 01:26:40,829 --> 01:26:43,062 What is their role in the universe? 1602 01:26:43,064 --> 01:26:46,833 Is their existence just a matter of chance? 1603 01:26:46,835 --> 01:26:49,169 Or are they connected in some larger way 1604 01:26:49,171 --> 01:26:52,205 to the very structure of the cosmos? 1605 01:26:52,207 --> 01:26:55,642 Supermassive black holes don't exist in isolation. 1606 01:26:55,644 --> 01:26:59,546 They seem to live in partnership with galaxies. 1607 01:26:59,548 --> 01:27:01,147 ♪ ♪ 1608 01:27:01,149 --> 01:27:03,917 Collections of millions, billions, 1609 01:27:03,919 --> 01:27:07,687 or even trillions of stars bound together by gravity, 1610 01:27:07,689 --> 01:27:12,358 galaxies are the fundamental building blocks of our universe. 1611 01:27:12,360 --> 01:27:16,029 So are the supermassive black holes at their centers 1612 01:27:16,031 --> 01:27:20,667 somehow fundamental to their very existence? 1613 01:27:20,669 --> 01:27:22,535 TYSON: We now just assume every galaxy, 1614 01:27:22,537 --> 01:27:24,804 even ones we have yet to confirm, 1615 01:27:24,806 --> 01:27:26,973 will have a supermassive black hole in their center. 1616 01:27:26,975 --> 01:27:30,710 KOCEVSKI: It could be that instead of simply being oddities, 1617 01:27:30,712 --> 01:27:32,912 that they are a key component to galaxies, 1618 01:27:32,914 --> 01:27:34,681 a key component to the universe. 1619 01:27:37,419 --> 01:27:39,085 We've come in a very short time to realize 1620 01:27:39,087 --> 01:27:42,322 that they likely inhabit the centers of all the galaxies. 1621 01:27:42,324 --> 01:27:44,557 And that can really only happen 1622 01:27:44,559 --> 01:27:46,593 if there's some symbiotic relationship 1623 01:27:46,595 --> 01:27:48,595 between the evolution of a galaxy 1624 01:27:48,597 --> 01:27:51,164 and the supermassive black hole in its core. 1625 01:27:53,134 --> 01:27:56,102 LEVIN: What could that relationship be? 1626 01:27:56,104 --> 01:27:59,706 One intriguing clue relates to size. 1627 01:27:59,708 --> 01:28:01,975 CHUNG-PEI MA: The bigger the galaxy is, 1628 01:28:01,977 --> 01:28:04,611 the more massive the black hole appears to be. 1629 01:28:04,613 --> 01:28:06,145 So these black holes at the center 1630 01:28:06,147 --> 01:28:09,148 seem to know about their larger-scale environment. 1631 01:28:10,452 --> 01:28:12,752 LEVIN: So which comes first, 1632 01:28:12,754 --> 01:28:16,189 the galaxy or the supermassive black hole? 1633 01:28:16,191 --> 01:28:18,358 It's not that simple. 1634 01:28:18,360 --> 01:28:22,529 It appears they somehow grow in tandem. 1635 01:28:22,531 --> 01:28:25,465 GHEZ: It's hard for one to form first and affect the other. 1636 01:28:25,467 --> 01:28:28,501 So today we think that whatever formed one 1637 01:28:28,503 --> 01:28:32,305 had to form the other as a by-product of that process. 1638 01:28:32,307 --> 01:28:35,441 And that there has to be some feedback mechanism 1639 01:28:35,443 --> 01:28:37,577 between the black hole and the galaxy 1640 01:28:37,579 --> 01:28:41,214 that keeps the growth of the two in lock sync. 1641 01:28:41,216 --> 01:28:43,449 ♪ ♪ 1642 01:28:43,451 --> 01:28:46,653 LEVIN: The way galaxies grow is by forming new stars 1643 01:28:46,655 --> 01:28:51,257 from clouds of hydrogen gas. 1644 01:28:51,259 --> 01:28:53,459 Gas is essentially the fuel for star formation, 1645 01:28:53,461 --> 01:28:55,228 just like gas is the fuel for our cars. 1646 01:28:55,230 --> 01:29:00,433 And so if you run out of gas, you run out of new stars. 1647 01:29:01,503 --> 01:29:03,102 LEVIN: So are supermassive black holes 1648 01:29:03,104 --> 01:29:07,440 somehow interfering with star formation? 1649 01:29:07,442 --> 01:29:09,142 GLIKMAN: When a black hole is growing, 1650 01:29:09,144 --> 01:29:10,643 a tremendous amount of energy is being liberated 1651 01:29:10,645 --> 01:29:14,047 and sent out into the galaxy. 1652 01:29:14,049 --> 01:29:16,816 And so we think that some of that energy goes to warm up gas. 1653 01:29:16,818 --> 01:29:20,987 And gas that's too warm will not form stars anymore. 1654 01:29:20,989 --> 01:29:27,126 ♪ ♪ 1655 01:29:27,128 --> 01:29:29,095 LEVIN: The heat produced by a growing black hole 1656 01:29:29,097 --> 01:29:32,632 makes it impossible for stars to form nearby. 1657 01:29:32,634 --> 01:29:34,601 ♪ ♪ 1658 01:29:34,603 --> 01:29:37,136 GLIKMAN: And so one way that a growing black hole 1659 01:29:37,138 --> 01:29:39,572 can influence its host galaxy 1660 01:29:39,574 --> 01:29:41,307 is by quenching the star formation. 1661 01:29:43,178 --> 01:29:45,545 LEVIN: In effect, the growth of the supermassive 1662 01:29:45,547 --> 01:29:50,483 determines whether or not its host galaxy grows or stagnates. 1663 01:29:50,485 --> 01:29:52,885 GALISON: They have a kind of eating phase, 1664 01:29:52,887 --> 01:29:55,221 and then a quiescent phase. 1665 01:29:55,223 --> 01:29:57,523 So they seem to be involved 1666 01:29:57,525 --> 01:29:59,459 with the formation of the galaxy in that way, 1667 01:29:59,461 --> 01:30:02,929 and then stabilizing of the galaxy at the same time. 1668 01:30:02,931 --> 01:30:06,866 LEVIN: So these mysterious supermassives 1669 01:30:06,868 --> 01:30:10,870 may actually control the building of the universe-- 1670 01:30:10,872 --> 01:30:13,239 not so much by their size, 1671 01:30:13,241 --> 01:30:19,045 but by the way the energy they generate shapes galaxies. 1672 01:30:19,047 --> 01:30:21,814 By mass, if you count up all the black holes in the universe, 1673 01:30:21,816 --> 01:30:23,783 the tiny ones as well as the supermassive ones, 1674 01:30:23,785 --> 01:30:25,518 the ultra-massive ones, 1675 01:30:25,520 --> 01:30:28,721 black holes are nothing. 1676 01:30:28,723 --> 01:30:33,126 However, energetically, how much power the galaxy gets 1677 01:30:33,128 --> 01:30:35,161 and at what time as it assembles, 1678 01:30:35,163 --> 01:30:40,333 seems to be dictated by the central black hole. 1679 01:30:40,335 --> 01:30:43,703 So they might well be the key players in the universe. 1680 01:30:43,705 --> 01:30:46,873 ♪ ♪ 1681 01:30:46,875 --> 01:30:50,610 LEVIN: In the next two years, NASA plans to launch 1682 01:30:50,612 --> 01:30:53,346 the James Webb Space Telescope. 1683 01:30:53,348 --> 01:30:56,883 Humanity's most powerful telescope ever, 1684 01:30:56,885 --> 01:31:00,286 the James Webb is designed to look in the infrared, 1685 01:31:00,288 --> 01:31:02,955 allowing it to see farther back in time than Hubble, 1686 01:31:02,957 --> 01:31:05,692 getting a look at the first stars and galaxies 1687 01:31:05,694 --> 01:31:09,095 that formed after the Big Bang. 1688 01:31:09,097 --> 01:31:12,865 Hopes are high that the James Webb Space Telescope 1689 01:31:12,867 --> 01:31:16,169 will help solve many of the remaining mysteries 1690 01:31:16,171 --> 01:31:19,238 about the earliest supermassive black holes. 1691 01:31:20,942 --> 01:31:25,812 TYSON: The James Webb Space Telescope is tuned specifically 1692 01:31:25,814 --> 01:31:30,416 to observe the early universe when galaxies were being born. 1693 01:31:30,418 --> 01:31:31,751 That could give us deeper understanding 1694 01:31:31,753 --> 01:31:33,820 of how you end up with a supermassive black hole 1695 01:31:33,822 --> 01:31:36,389 in your galaxy to begin with. 1696 01:31:37,826 --> 01:31:39,559 GHEZ: Technology is moving really fast, 1697 01:31:39,561 --> 01:31:43,563 and as a result, we have really fundamental new views 1698 01:31:43,565 --> 01:31:45,498 of the universe. 1699 01:31:45,500 --> 01:31:49,402 I think we are really living in a golden era of astronomy. 1700 01:31:49,404 --> 01:31:53,172 ♪ ♪ 1701 01:31:53,174 --> 01:31:54,874 LEVIN: And the James Webb Space Telescope 1702 01:31:54,876 --> 01:31:58,211 isn't the only new development that promises to solve 1703 01:31:58,213 --> 01:32:01,013 some of the mysteries around black holes. 1704 01:32:01,015 --> 01:32:06,252 ♪ ♪ 1705 01:32:07,756 --> 01:32:09,188 WOMAN: I believe have infrared components... 1706 01:32:09,190 --> 01:32:10,623 LEVIN: A group of scientists 1707 01:32:10,625 --> 01:32:13,392 led by Shep Doeleman 1708 01:32:13,394 --> 01:32:16,028 is now attempting the impossible: 1709 01:32:16,030 --> 01:32:20,199 to take a picture of a black hole. 1710 01:32:20,201 --> 01:32:23,002 DOELEMAN: It's interesting that we can say something 1711 01:32:23,004 --> 01:32:26,105 about the accretion flow near the black hole at all. 1712 01:32:26,107 --> 01:32:28,941 OZEL: And if some of this linear behavior survives, 1713 01:32:28,943 --> 01:32:31,978 maybe we'll have a way of interpreting it. 1714 01:32:31,980 --> 01:32:35,648 LEVIN: The project is called the Event Horizon Telescope. 1715 01:32:35,650 --> 01:32:39,752 DOELEMAN: The basic goal of the Event Horizon Telescope 1716 01:32:39,754 --> 01:32:41,387 is really to see the unseeable. 1717 01:32:41,389 --> 01:32:42,755 It's to bring into focus 1718 01:32:42,757 --> 01:32:45,158 something that science has told us for many, many years 1719 01:32:45,160 --> 01:32:48,361 is precisely something we can't observe-- 1720 01:32:48,363 --> 01:32:49,996 the black hole. 1721 01:32:51,266 --> 01:32:55,334 LEVIN: Their primary target is Sagittarius A , 1722 01:32:55,336 --> 01:33:00,139 the supermassive in the center of our Milky Way Galaxy. 1723 01:33:00,141 --> 01:33:04,076 They're using a global network of radio telescopes. 1724 01:33:04,078 --> 01:33:07,180 DOELEMAN: We need good weather at eight different telescopes 1725 01:33:07,182 --> 01:33:08,147 all around the world, 1726 01:33:08,149 --> 01:33:09,615 and that is a tall order. 1727 01:33:09,617 --> 01:33:12,852 LEVIN: But if black holes are invisible, 1728 01:33:12,854 --> 01:33:17,089 what exactly do they hope to photograph? 1729 01:33:17,091 --> 01:33:19,158 What we are trying to photograph really is the shadow. 1730 01:33:19,160 --> 01:33:23,996 So as this gas around the black hole 1731 01:33:23,998 --> 01:33:26,833 swirls inwards and actually hits the event horizon, 1732 01:33:26,835 --> 01:33:28,301 it leaves a silhouette, 1733 01:33:28,303 --> 01:33:33,206 a very well defined shadow on the surrounding light. 1734 01:33:33,208 --> 01:33:35,541 So really it should look like a donut, 1735 01:33:35,543 --> 01:33:37,944 with its very well defined hole. 1736 01:33:37,946 --> 01:33:40,246 And that's the picture that we're after. 1737 01:33:40,248 --> 01:33:41,981 If I convert that into frequencies, 1738 01:33:41,983 --> 01:33:44,150 I get two-pi-square there. 1739 01:33:44,152 --> 01:33:47,687 LEVIN: The team has conducted their first observing run 1740 01:33:47,689 --> 01:33:50,456 and is processing the data now. 1741 01:33:50,458 --> 01:33:52,291 Okay, you're saying the velocity... 1742 01:33:52,293 --> 01:33:54,493 LEVIN: It's hoped that these new technologies 1743 01:33:54,495 --> 01:33:57,730 will give us an unprecedented view of black holes 1744 01:33:57,732 --> 01:33:58,965 in our universe. 1745 01:33:58,967 --> 01:34:01,167 But there is one new technology 1746 01:34:01,169 --> 01:34:03,970 that is already delivering results. 1747 01:34:03,972 --> 01:34:07,540 And that brings us back here, to LIGO, 1748 01:34:07,542 --> 01:34:10,676 a key player in the black hole drama, 1749 01:34:10,678 --> 01:34:15,481 to an idea that took root way ahead of its time: 1750 01:34:15,483 --> 01:34:17,717 gravitational waves. 1751 01:34:17,719 --> 01:34:21,954 With general relativity, his theory of gravity, 1752 01:34:21,956 --> 01:34:25,491 Einstein predicts that when an object moves, 1753 01:34:25,493 --> 01:34:29,629 it can create ripples in space and time-- 1754 01:34:29,631 --> 01:34:34,133 an actual squeezing and stretching of space itself. 1755 01:34:34,135 --> 01:34:36,969 One of the holy grails of 20th-century physics 1756 01:34:36,971 --> 01:34:40,973 was to detect these gravitational waves. 1757 01:34:40,975 --> 01:34:42,942 WEISS: That was not easy to do 1758 01:34:42,944 --> 01:34:44,143 with general relativity, 1759 01:34:44,145 --> 01:34:46,579 because all the effects that you could think of 1760 01:34:46,581 --> 01:34:48,981 were infinitesimally small. 1761 01:34:48,983 --> 01:34:50,449 Very, very difficult to measure. 1762 01:34:50,451 --> 01:34:53,286 LEVIN: The thinking was, 1763 01:34:53,288 --> 01:34:55,888 if gravitational waves could be measured, 1764 01:34:55,890 --> 01:34:58,891 it would confirm Einstein's prediction. 1765 01:34:58,893 --> 01:35:00,860 And there could be an added benefit-- 1766 01:35:00,862 --> 01:35:06,065 it might also prove the existence of black holes 1767 01:35:06,067 --> 01:35:11,037 and help solve the mystery of how supermassives grow. 1768 01:35:11,039 --> 01:35:15,041 But how to detect gravitational waves? 1769 01:35:15,043 --> 01:35:18,844 In 1970, the problem caught the attention 1770 01:35:18,846 --> 01:35:23,115 of a young experimental physicist, Rai Weiss. 1771 01:35:23,117 --> 01:35:26,852 (classical music playing) 1772 01:35:26,854 --> 01:35:32,725 Rai had the perfect background to hunt for gravitational waves. 1773 01:35:32,727 --> 01:35:37,063 For decades, he'd been working with more familiar waves-- 1774 01:35:37,065 --> 01:35:38,731 sound waves. 1775 01:35:38,733 --> 01:35:39,966 WEISS: We were immigrants, 1776 01:35:39,968 --> 01:35:41,600 we were German Jews. 1777 01:35:41,602 --> 01:35:43,803 And a lot of our friends were very, very interested in music. 1778 01:35:43,805 --> 01:35:45,271 (music continues) 1779 01:35:45,273 --> 01:35:46,739 LEVIN: Rai devoted himself 1780 01:35:46,741 --> 01:35:49,675 to coaxing every subtle nuance he could 1781 01:35:49,677 --> 01:35:52,178 out of recorded music. 1782 01:35:52,180 --> 01:35:54,747 WEISS: Those records had a terrible problem. 1783 01:35:54,749 --> 01:35:57,550 When the music was loud, it sounded wonderful. 1784 01:35:57,552 --> 01:35:59,852 When the music was real quiet and slow, 1785 01:35:59,854 --> 01:36:00,953 what you heard was this... 1786 01:36:00,955 --> 01:36:02,455 (imitating hissing) ...like that. 1787 01:36:02,457 --> 01:36:05,758 A hissing noise. 1788 01:36:05,760 --> 01:36:07,660 And that was so annoying. 1789 01:36:08,496 --> 01:36:09,929 LEVIN: The lessons he learns 1790 01:36:09,931 --> 01:36:11,664 trying to eliminate noise in recordings 1791 01:36:11,666 --> 01:36:13,866 will pay off later, 1792 01:36:13,868 --> 01:36:15,201 when Rai turns his attention 1793 01:36:15,203 --> 01:36:18,404 to detecting gravitational waves. 1794 01:36:18,406 --> 01:36:19,638 WEISS: You have to understand 1795 01:36:19,640 --> 01:36:22,508 how a gravitational wave does its dirty work. 1796 01:36:22,510 --> 01:36:24,543 LEVIN: As a physics problem, 1797 01:36:24,545 --> 01:36:28,981 gravitational waves are not unlike sound waves. 1798 01:36:28,983 --> 01:36:30,583 Let's suppose the wave comes from something 1799 01:36:30,585 --> 01:36:33,619 that is in some way moving and oscillating. 1800 01:36:33,621 --> 01:36:35,388 (vibrating) 1801 01:36:35,390 --> 01:36:38,891 LEVIN: A sound wave compresses and expands air. 1802 01:36:38,893 --> 01:36:43,262 A gravitational wave compresses and expands space 1803 01:36:43,264 --> 01:36:45,197 and everything in it. 1804 01:36:45,199 --> 01:36:48,134 WEISS: If a wave came through the Earth, 1805 01:36:48,136 --> 01:36:49,635 it would cause space 1806 01:36:49,637 --> 01:36:54,206 to expand momentarily and then contract again. 1807 01:36:54,208 --> 01:36:57,209 It keeps doing it, so it's this thing 1808 01:36:57,211 --> 01:36:59,445 that goes blip, blip, blip, right along like that. 1809 01:37:00,782 --> 01:37:02,214 LEVIN: So how to measure 1810 01:37:02,216 --> 01:37:06,452 the extremely tiny expansion and contraction of space? 1811 01:37:08,556 --> 01:37:11,190 Rai's idea was to use light. 1812 01:37:11,192 --> 01:37:13,292 Send a beam of light 1813 01:37:13,294 --> 01:37:14,827 from one place to another, 1814 01:37:14,829 --> 01:37:17,496 and measure the time it takes to get there. 1815 01:37:17,498 --> 01:37:18,998 (clicks) 1816 01:37:19,000 --> 01:37:22,234 That's how the exact distance to the moon was calculated: 1817 01:37:22,236 --> 01:37:25,104 bouncing a laser beam from the Earth 1818 01:37:25,106 --> 01:37:29,508 off a mirror left behind by Apollo 11 astronauts. 1819 01:37:29,510 --> 01:37:34,246 ♪ ♪ 1820 01:37:34,248 --> 01:37:35,848 From the duration of the round trip, 1821 01:37:35,850 --> 01:37:39,919 scientists could determine the distance. 1822 01:37:39,921 --> 01:37:42,321 ♪ ♪ 1823 01:37:42,323 --> 01:37:45,291 Rai came up with an ingenious design 1824 01:37:45,293 --> 01:37:48,194 for an instrument that uses lasers and mirrors 1825 01:37:48,196 --> 01:37:51,697 to detect the faint expansions and contractions of space 1826 01:37:51,699 --> 01:37:55,101 that would be caused by a gravitational wave. 1827 01:37:55,103 --> 01:37:59,538 It's called a laser interferometer. 1828 01:37:59,540 --> 01:38:03,676 It works by firing a laser into a splitter. 1829 01:38:03,678 --> 01:38:05,544 Half of the light continues straight ahead 1830 01:38:05,546 --> 01:38:07,780 towards one mirror, 1831 01:38:07,782 --> 01:38:11,517 while the other half is sent towards another mirror. 1832 01:38:11,519 --> 01:38:13,719 The distant mirrors bounce the light beams back, 1833 01:38:13,721 --> 01:38:19,058 where they rejoin at a photo detector. 1834 01:38:19,060 --> 01:38:22,761 If the distances the two beams travel are exactly the same, 1835 01:38:22,763 --> 01:38:27,500 the system is designed so the two beams cancel each other out; 1836 01:38:27,502 --> 01:38:31,904 the detector sees nothing. 1837 01:38:31,906 --> 01:38:34,940 You've set the trap to measure the gravitational wave. 1838 01:38:34,942 --> 01:38:37,276 Now comes the gravitational wave that's coming, 1839 01:38:37,278 --> 01:38:38,577 let's say, at this structure. 1840 01:38:38,579 --> 01:38:42,114 LEVIN: If a gravitational wave passes through, 1841 01:38:42,116 --> 01:38:44,850 it briefly changes the length of the arms. 1842 01:38:44,852 --> 01:38:48,454 The light beams no longer arrive back at the same time 1843 01:38:48,456 --> 01:38:51,290 to cancel each other out. 1844 01:38:51,292 --> 01:38:53,926 A gravitational wave hits. 1845 01:38:53,928 --> 01:38:56,395 Light appears at the detector. 1846 01:38:56,397 --> 01:38:59,298 The trap has sprung. 1847 01:38:59,300 --> 01:39:00,499 That's the basic idea. 1848 01:39:00,501 --> 01:39:02,368 It's a very straightforward measurement. 1849 01:39:04,071 --> 01:39:07,439 LEVIN: A clever idea, and simple in principle. 1850 01:39:07,441 --> 01:39:09,708 But the devil-- 1851 01:39:09,710 --> 01:39:11,277 and the Nobel Prize-- 1852 01:39:11,279 --> 01:39:13,412 lie in the details. 1853 01:39:13,414 --> 01:39:16,749 The difference in length between the two arms 1854 01:39:16,751 --> 01:39:20,219 would be tiny beyond imagining. 1855 01:39:20,221 --> 01:39:21,353 How tiny? 1856 01:39:21,355 --> 01:39:22,521 Well, take the size of an atom. 1857 01:39:22,523 --> 01:39:24,657 It's less than that. 1858 01:39:24,659 --> 01:39:27,393 Go down by a factor of 100,000. 1859 01:39:27,395 --> 01:39:28,994 That's the nucleus of an atom. 1860 01:39:28,996 --> 01:39:30,829 It's less than that. 1861 01:39:30,831 --> 01:39:34,466 It was 100 times below that. 1862 01:39:34,468 --> 01:39:39,171 So we're talking about really itsy-bitsy, teeny-weeny. 1863 01:39:39,173 --> 01:39:41,907 I thought it was crazy. 1864 01:39:41,909 --> 01:39:44,843 I think everybody's initial reaction to the idea 1865 01:39:44,845 --> 01:39:47,379 was, this is going to be impossible. 1866 01:39:47,381 --> 01:39:52,851 LEVIN: In 1973, Kip Thorne puts his skepticism on the record 1867 01:39:52,853 --> 01:39:54,653 in a classic textbook, 1868 01:39:54,655 --> 01:39:56,422 doubting it will ever work. 1869 01:39:56,424 --> 01:39:59,291 But Kip has never heard Rai Weiss 1870 01:39:59,293 --> 01:40:02,127 explain his plan in detail. 1871 01:40:02,129 --> 01:40:04,997 And when he does... 1872 01:40:04,999 --> 01:40:06,699 We spent the whole night talking. 1873 01:40:06,701 --> 01:40:09,235 And so I said, "No, no, no, it's very possible." 1874 01:40:09,237 --> 01:40:13,405 And within no time at all, 20 minutes, maybe half an hour, 1875 01:40:13,407 --> 01:40:16,875 Kip was solidly understanding this thing and he says, "Yup!" 1876 01:40:16,877 --> 01:40:19,178 And I ate crow the rest of my career, 1877 01:40:19,180 --> 01:40:22,147 because once I had talked with Ray about it in detail, 1878 01:40:22,149 --> 01:40:24,850 I decided I would spend a large fraction 1879 01:40:24,852 --> 01:40:25,818 of the rest of my career 1880 01:40:25,820 --> 01:40:28,454 helping the experimenters. 1881 01:40:30,591 --> 01:40:33,559 LEVIN: But it will take 40 years, 1882 01:40:33,561 --> 01:40:35,327 and enormous sums of money, 1883 01:40:35,329 --> 01:40:40,099 to bring Rai and Kip's vision to reality. 1884 01:40:40,101 --> 01:40:43,636 Getting LIGO funded 1885 01:40:43,638 --> 01:40:45,671 was extremely controversial. 1886 01:40:45,673 --> 01:40:48,007 Hundreds of millions of dollars 1887 01:40:48,009 --> 01:40:52,011 to detect a signal that had never been seen before. 1888 01:40:53,547 --> 01:40:56,115 There were many people who feared 1889 01:40:56,117 --> 01:40:59,852 that LIGO would suck the money out of the room. 1890 01:40:59,854 --> 01:41:04,056 And so there was a lot of controversy. 1891 01:41:04,058 --> 01:41:06,091 What everybody could agree on was, 1892 01:41:06,093 --> 01:41:09,795 this was extremely difficult. 1893 01:41:09,797 --> 01:41:13,299 LEVIN: With such a sensitive instrument, 1894 01:41:13,301 --> 01:41:15,701 one of the biggest challenges 1895 01:41:15,703 --> 01:41:20,572 is Rai Weiss's old hi-fi nemesis: noise. 1896 01:41:20,574 --> 01:41:22,975 Ground motion. 1897 01:41:22,977 --> 01:41:24,443 The seismic motion of the Earth. 1898 01:41:24,445 --> 01:41:26,245 Acoustics' noise, 1899 01:41:26,247 --> 01:41:28,113 sounds... (thunder crashing) 1900 01:41:28,115 --> 01:41:31,483 Everything would tend to move that mirror. 1901 01:41:31,485 --> 01:41:35,387 LEVIN: Turns out, even the emptiness of a total vacuum 1902 01:41:35,389 --> 01:41:38,424 creates a potentially crippling problem. 1903 01:41:38,426 --> 01:41:41,193 At subatomic distances, 1904 01:41:41,195 --> 01:41:43,762 the weird randomness of the quantum world 1905 01:41:43,764 --> 01:41:46,932 causes a ruckus in the mirrors. 1906 01:41:46,934 --> 01:41:50,669 THORNE: This quantum noise is due to quantum fluctuations. 1907 01:41:50,671 --> 01:41:54,440 These mirrors are doing what an electron does inside an atom; 1908 01:41:54,442 --> 01:41:55,641 they're jiggling around. 1909 01:41:55,643 --> 01:41:58,944 ♪ ♪ 1910 01:41:58,946 --> 01:42:01,280 LEVIN: Exquisite sensitivity, 1911 01:42:01,282 --> 01:42:03,282 extreme vacuum, 1912 01:42:03,284 --> 01:42:05,517 hundreds of thousands of electronic circuits... 1913 01:42:06,620 --> 01:42:09,455 LIGO is one of the most complex instruments 1914 01:42:09,457 --> 01:42:12,925 in the history of science. 1915 01:42:12,927 --> 01:42:17,730 And as a final means of eliminating false signals, 1916 01:42:17,732 --> 01:42:18,931 they build not one, 1917 01:42:18,933 --> 01:42:22,201 but two complete installations: 1918 01:42:22,203 --> 01:42:28,173 one in Washington state and another in Louisiana. 1919 01:42:28,175 --> 01:42:29,808 And so the LIGO designers did it right. 1920 01:42:29,810 --> 01:42:31,477 They designed more than one detector, 1921 01:42:31,479 --> 01:42:35,748 separated from one another by great distances, 1922 01:42:35,750 --> 01:42:39,051 so that if you detect something in one and not in the other, 1923 01:42:39,053 --> 01:42:42,721 then, you know, go back and check your electronics. 1924 01:42:42,723 --> 01:42:45,824 Check to see if it was April Fools' Day 1925 01:42:45,826 --> 01:42:48,026 and somebody didn't just tweak the knobs. 1926 01:42:48,028 --> 01:42:50,562 ♪ ♪ 1927 01:42:50,564 --> 01:42:53,298 LEVIN: Early fall 2015. 1928 01:42:53,300 --> 01:42:55,667 Both locations are operating, 1929 01:42:55,669 --> 01:42:58,971 but the first official science run has not yet begun. 1930 01:42:58,973 --> 01:43:02,007 They're still testing. 1931 01:43:03,978 --> 01:43:07,913 In the early hours of Sunday, September 14, 2015, 1932 01:43:07,915 --> 01:43:12,384 a scientist in Louisiana makes a fateful decision. 1933 01:43:12,386 --> 01:43:17,022 ♪ ♪ 1934 01:43:17,024 --> 01:43:20,426 Robert Schofield has been working all weekend 1935 01:43:20,428 --> 01:43:23,095 doing final calibrations. 1936 01:43:23,097 --> 01:43:25,697 All righty, let's take a spectrum. 1937 01:43:25,699 --> 01:43:28,000 LEVIN: He has one last test. 1938 01:43:28,002 --> 01:43:31,603 SCHOFIELD: So let's see where this computer's getting its power. 1939 01:43:31,605 --> 01:43:35,107 LEVIN: But it's late, and the equipment is not cooperating. 1940 01:43:35,109 --> 01:43:39,945 SCHOFIELD: It was about 4:00 or so in the morning, 1941 01:43:39,947 --> 01:43:43,582 and we still had about another hour of work to do. 1942 01:43:43,584 --> 01:43:47,019 And we were, like, "Yeah, things aren't working so well, 1943 01:43:47,021 --> 01:43:48,987 "and I'm really tired. 1944 01:43:48,989 --> 01:43:51,323 Let's not do this last hour or so of work." 1945 01:43:54,595 --> 01:43:56,762 LEVIN: They call it a night. 1946 01:43:56,764 --> 01:43:58,831 And 40 minutes later, 1947 01:43:58,833 --> 01:44:01,800 in the silence of their inactivity, 1948 01:44:01,802 --> 01:44:04,670 they open the door to history. 1949 01:44:04,672 --> 01:44:09,508 ♪ ♪ 1950 01:44:18,819 --> 01:44:19,952 (faint chirp) 1951 01:44:22,089 --> 01:44:25,858 A powerful gravitational wave rumbles through both detectors, 1952 01:44:25,860 --> 01:44:29,661 Louisiana and Washington. 1953 01:44:29,663 --> 01:44:33,131 Had Robert Schofield worked 40 more minutes that night, 1954 01:44:33,133 --> 01:44:35,100 with the instruments in test mode, 1955 01:44:35,102 --> 01:44:39,037 a signal that had been on its way for 1.3 billion years 1956 01:44:39,039 --> 01:44:42,608 would never have been recorded. 1957 01:44:42,610 --> 01:44:43,976 SCHOFIELD: I like to say, 1958 01:44:43,978 --> 01:44:46,311 you know, one of my biggest contributions to LIGO 1959 01:44:46,313 --> 01:44:49,748 has been my laziness that day. 1960 01:44:49,750 --> 01:44:53,785 (indistinct conversations) 1961 01:44:53,787 --> 01:44:55,888 I got an email from somebody here saying, 1962 01:44:55,890 --> 01:44:59,892 "Hey, look, look at this place on the web." 1963 01:44:59,894 --> 01:45:02,160 (chirps) 1964 01:45:02,162 --> 01:45:06,098 I looked at that and I said, "Holy (bleep)!" 1965 01:45:06,100 --> 01:45:08,066 ♪ ♪ 1966 01:45:08,068 --> 01:45:09,067 (chirps) 1967 01:45:09,069 --> 01:45:10,636 THORNE: It was so strong 1968 01:45:10,638 --> 01:45:13,605 that you could see it by eye in the data. 1969 01:45:13,607 --> 01:45:16,808 It was too good to be true. 1970 01:45:16,810 --> 01:45:18,610 LEVIN: But it was true. 1971 01:45:18,612 --> 01:45:22,514 In fact it was loud, and surprisingly clear. 1972 01:45:22,516 --> 01:45:23,815 And it just sang at you. 1973 01:45:23,817 --> 01:45:25,150 There it was, standing out. 1974 01:45:27,054 --> 01:45:30,756 LEVIN: The signal lasted less than a second, 1975 01:45:30,758 --> 01:45:33,125 but in that briefest of moments 1976 01:45:33,127 --> 01:45:35,627 it delivered a cosmically profound message 1977 01:45:35,629 --> 01:45:38,730 more than a billion years in the making, 1978 01:45:38,732 --> 01:45:43,802 proving the existence of black holes. 1979 01:45:43,804 --> 01:45:45,437 THORNE: So what we saw in the signal 1980 01:45:45,439 --> 01:45:49,141 involved oscillations of the mirrors that were slow at first, 1981 01:45:49,143 --> 01:45:51,677 became faster and faster and faster. 1982 01:45:51,679 --> 01:45:54,613 And this was precisely the kind of behavior 1983 01:45:54,615 --> 01:45:57,449 that you would expect from gravitational waves 1984 01:45:57,451 --> 01:46:01,853 caused by two black holes going around each other, 1985 01:46:01,855 --> 01:46:03,221 spiraling together. 1986 01:46:04,425 --> 01:46:07,025 LEVIN: Two massive black holes, 1987 01:46:07,027 --> 01:46:09,261 one 29 times the mass of the sun, 1988 01:46:09,263 --> 01:46:13,498 the other 36 times the mass of the sun, 1989 01:46:13,500 --> 01:46:17,069 whipping around each other hundreds of times a second, 1990 01:46:17,071 --> 01:46:21,940 finally completing their act of mutual destruction by merging... 1991 01:46:25,279 --> 01:46:31,116 Creating a single, larger black hole of 62 solar masses. 1992 01:46:32,419 --> 01:46:36,121 The violent merger converts some of the mass 1993 01:46:36,123 --> 01:46:38,724 into an apocalyptic release of energy 1994 01:46:38,726 --> 01:46:42,327 beyond anything ever before witnessed. 1995 01:46:42,329 --> 01:46:44,529 THORNE: The collision, in effect, 1996 01:46:44,531 --> 01:46:48,734 creates a very-- a veritable storm in the fabric or the shape 1997 01:46:48,736 --> 01:46:49,935 of space and time, 1998 01:46:49,937 --> 01:46:52,871 as though you had taken three suns, 1999 01:46:52,873 --> 01:46:57,009 you had annihilated them completely, 2000 01:46:57,011 --> 01:46:59,811 converted it into gravitational waves. 2001 01:46:59,813 --> 01:47:04,383 The power was 50 times higher than the output power 2002 01:47:04,385 --> 01:47:07,119 of all the stars in the universe put together-- 2003 01:47:07,121 --> 01:47:10,155 in a fraction of a second. 2004 01:47:10,157 --> 01:47:12,891 But the most powerful explosion 2005 01:47:12,893 --> 01:47:17,229 that humans have ever had any evidence for 2006 01:47:17,231 --> 01:47:19,531 with the exception of the Big Bang. 2007 01:47:19,533 --> 01:47:21,500 ♪ ♪ 2008 01:47:21,502 --> 01:47:25,303 LEVIN: Since that very first signal in September 2015, 2009 01:47:25,305 --> 01:47:30,375 LIGO has detected several more collisions of black holes. 2010 01:47:30,377 --> 01:47:36,348 In October 2017, Rai Weiss, Kip Thorne, 2011 01:47:36,350 --> 01:47:38,884 and LIGO's former director Barry Barisch 2012 01:47:38,886 --> 01:47:42,454 received the Nobel Prize. 2013 01:47:42,456 --> 01:47:48,026 The LIGO discoveries prove that black holes can merge-- 2014 01:47:48,028 --> 01:47:51,630 one way they can grow bigger quickly. 2015 01:47:53,534 --> 01:47:56,368 More and more evidence of these merging black holes tells us 2016 01:47:56,370 --> 01:47:59,137 there are a lot of these stellar black holes around, 2017 01:47:59,139 --> 01:48:00,739 that they can find each other and, and merge. 2018 01:48:00,741 --> 01:48:06,411 LEVIN: And the discovery opened an entirely new way 2019 01:48:06,413 --> 01:48:09,181 of observing the universe. 2020 01:48:09,183 --> 01:48:12,384 ♪ ♪ 2021 01:48:12,386 --> 01:48:13,452 (chirp) 2022 01:48:13,454 --> 01:48:14,886 We always thought of astronomy 2023 01:48:14,888 --> 01:48:17,055 as an observational field 2024 01:48:17,057 --> 01:48:20,258 where we are looking at radiation. 2025 01:48:20,260 --> 01:48:23,328 We are seeing things. 2026 01:48:23,330 --> 01:48:24,696 But this is not radiation. 2027 01:48:24,698 --> 01:48:26,431 This is something much more fundamental. 2028 01:48:26,433 --> 01:48:31,770 These are sort of fundamental tremors in space-time itself. 2029 01:48:31,772 --> 01:48:34,473 We can now hear the universe. 2030 01:48:34,475 --> 01:48:41,446 ♪ ♪ 2031 01:48:41,448 --> 01:48:43,949 LEVIN: For the first time, 2032 01:48:43,951 --> 01:48:48,086 astronomers have simultaneously seen and heard a cosmic event. 2033 01:48:48,088 --> 01:48:51,590 ♪ ♪ 2034 01:48:51,592 --> 01:48:57,028 In August 2017, LIGO detected gravitational waves 2035 01:48:57,030 --> 01:49:00,665 from a collision of two neutron stars. 2036 01:49:00,667 --> 01:49:03,535 Black holes are empty space, 2037 01:49:03,537 --> 01:49:06,505 but neutron stars are dense dead stars 2038 01:49:06,507 --> 01:49:09,541 that can crash together and light up the skies. 2039 01:49:09,543 --> 01:49:13,712 ♪ ♪ 2040 01:49:13,714 --> 01:49:16,681 When telescopes and satellites around the globe 2041 01:49:16,683 --> 01:49:20,218 pointed in the direction of the sound, 2042 01:49:20,220 --> 01:49:23,488 the world saw fireworks 2043 01:49:23,490 --> 01:49:27,192 in an explosive collision and afterglow. 2044 01:49:27,194 --> 01:49:29,961 Possibly, the collision resulted in the creation 2045 01:49:29,963 --> 01:49:32,531 of a new black hole. 2046 01:49:35,836 --> 01:49:39,805 But unless we observe the formation of a black hole, 2047 01:49:39,807 --> 01:49:42,641 there is much we will never know. 2048 01:49:42,643 --> 01:49:44,342 Because so much about black holes 2049 01:49:44,344 --> 01:49:46,044 is irretrievably out of our reach, 2050 01:49:46,046 --> 01:49:48,180 we can never know where they came from, 2051 01:49:48,182 --> 01:49:50,382 what's inside, or their history. 2052 01:49:50,384 --> 01:49:53,418 ♪ ♪ 2053 01:49:53,420 --> 01:49:55,987 (explosion roars) 2054 01:49:55,989 --> 01:49:58,456 But we can imagine their future. 2055 01:49:58,458 --> 01:50:02,494 The number of black holes in the universe is increasing. 2056 01:50:02,496 --> 01:50:05,630 And they're getting bigger. 2057 01:50:05,632 --> 01:50:08,867 Stars collapse, 2058 01:50:08,869 --> 01:50:10,836 black holes feed and merge, 2059 01:50:10,838 --> 01:50:14,039 new ones form. 2060 01:50:14,041 --> 01:50:15,974 Could it be that one day, 2061 01:50:15,976 --> 01:50:18,977 everything will end up inside them 2062 01:50:18,979 --> 01:50:21,513 and they will rule the universe? 2063 01:50:21,515 --> 01:50:23,748 ♪ ♪ 2064 01:50:23,750 --> 01:50:28,353 Untold trillions upon trillions of years after this happens, 2065 01:50:28,355 --> 01:50:31,857 and the last bits of matter cross their event horizons, 2066 01:50:31,859 --> 01:50:35,227 black holes themselves may radiate away 2067 01:50:35,229 --> 01:50:39,664 and vanish from this reality. 2068 01:50:39,666 --> 01:50:42,067 ♪ ♪ 2069 01:50:43,670 --> 01:50:46,671 Their mysteries are many, and we're just starting 2070 01:50:46,673 --> 01:50:51,243 to unlock the secrets of these strange, powerful places. 2071 01:50:52,312 --> 01:50:54,613 But one thing is certain. 2072 01:50:54,615 --> 01:50:59,084 Black holes will continue to intrigue us, 2073 01:50:59,086 --> 01:51:00,785 tantalize us, 2074 01:51:00,787 --> 01:51:06,691 and challenge both our science and our imaginations. 2075 01:51:06,693 --> 01:51:12,530 ♪ ♪ 2076 01:51:26,713 --> 01:51:30,882 ♪ ♪ 2077 01:51:58,412 --> 01:52:01,012 This "NOVA" program is available on DVD. 2078 01:52:01,014 --> 01:52:06,451 To order, visit shopPBS.org or call 1-800-PLAY-PBS. 2079 01:52:06,453 --> 01:52:09,821 "NOVA" is also available for download on iTunes. 2080 01:52:12,726 --> 01:52:17,496 ♪ ♪