1 00:00:09,807 --> 00:00:13,117 Humanity, ignorant in bliss. 2 00:00:16,527 --> 00:00:22,682 We go about our lives unaware that in the depths of space lurk invisible monsters. 3 00:00:29,007 --> 00:00:32,682 Destroyers powerful enough to tear apart our sun 4 00:00:32,847 --> 00:00:36,965 and leave our Earth a shattered, burned-out ruin. 5 00:00:45,047 --> 00:00:50,201 You are about to enter the world of the universe's ultimate killer. 6 00:00:56,487 --> 00:01:01,800 We will be there when the monster is created - in the heart of a dying star. 7 00:01:04,567 --> 00:01:09,322 We will search for its telltale signs in the darkness of deep space. 8 00:01:09,487 --> 00:01:15,960 This is the story of the power that may one day destroy us all - the black hole. 9 00:01:47,607 --> 00:01:50,485 There's an old saying - what goes up... 10 00:01:51,487 --> 00:01:55,685 ..must come down. Thing is, it's not always true. 11 00:01:55,847 --> 00:01:59,601 If you throw something hard enough, it might never come down. 12 00:02:04,567 --> 00:02:08,958 If something goes up fast enough, it can escape the Earth altogether. 13 00:02:10,687 --> 00:02:14,282 Faster still, and it can escape the immense pull of our sun, 14 00:02:14,447 --> 00:02:17,405 the force that holds the planets in place. 15 00:02:33,287 --> 00:02:38,122 Travel fast enough, and you can even escape the pull of the billions of stars 16 00:02:38,287 --> 00:02:40,676 that make up our galaxy... 17 00:02:43,607 --> 00:02:46,075 ..the Milky Way. 18 00:02:56,207 --> 00:03:00,917 But there is one object out there whose pull is so powerful you can never escape, 19 00:03:01,087 --> 00:03:05,763 no matter how fast you go, not even if you travel at the speed of light. 20 00:03:08,607 --> 00:03:11,360 Meet the monster. 21 00:03:16,167 --> 00:03:18,920 This is a black hole in action. 22 00:03:19,087 --> 00:03:23,046 It is tearing apart a star that has strayed too close. 23 00:03:25,127 --> 00:03:28,563 Anything that comes near is destroyed. 24 00:03:34,527 --> 00:03:39,726 It's hard to believe anything is powerful enough to destroy a planet or a star, 25 00:03:39,887 --> 00:03:42,196 but it's true. 26 00:03:48,407 --> 00:03:51,285 Let's take a closer look. 27 00:03:51,447 --> 00:03:55,804 Put a black hole near something and immediately it starts ripping it apart. 28 00:03:59,407 --> 00:04:02,604 There's a star in there - it could just as easily be our sun - 29 00:04:02,767 --> 00:04:06,396 and it is being pulled apart by a black hole. 30 00:04:13,127 --> 00:04:17,803 On this scale, our Earth would be no bigger than a pebble. 31 00:04:20,807 --> 00:04:23,526 We wouldn't stand a chance. 32 00:04:29,887 --> 00:04:33,243 The shocking thing is how small the black hole is. 33 00:04:33,407 --> 00:04:37,082 The black hole itself is right at the centre of the disc. It's tiny. 34 00:04:40,727 --> 00:04:43,719 It's a million times smaller than the star. 35 00:04:43,887 --> 00:04:46,276 Just look what it can do. 36 00:04:49,887 --> 00:04:53,766 What is it about a black hole that makes it so powerful? 37 00:04:59,007 --> 00:05:01,567 The answer is gravity. 38 00:05:01,727 --> 00:05:05,402 It's the force that keeps us all stuck to the surface of our planet. 39 00:05:08,647 --> 00:05:11,923 If something's heavy enough, it pulls YOU towards it. 40 00:05:12,087 --> 00:05:15,079 And planet Earth is heavy - 41 00:05:15,247 --> 00:05:18,717 so heavy, in fact, that to get off it, you have to do this. 42 00:05:34,927 --> 00:05:38,920 All of this, just to escape from our tiny globe. 43 00:05:53,087 --> 00:05:55,760 And if Earth's gravity seems strong... 44 00:05:57,447 --> 00:06:00,245 ..imagine the pull of the sun. 45 00:06:00,407 --> 00:06:03,080 Our sun is a million kilometres across. 46 00:06:03,247 --> 00:06:06,717 This is the real heavyweight of the solar system. 47 00:06:08,327 --> 00:06:12,206 But if you think our sun is big, think again. 48 00:06:18,527 --> 00:06:24,363 There are stars out there that are vast. Their gravity is mind-boggling. 49 00:06:28,727 --> 00:06:32,686 But compared to a black hole, even this star is a weakling. 50 00:06:32,847 --> 00:06:35,998 A black hole weighs as much as a massive star, 51 00:06:36,167 --> 00:06:40,206 but it's crammed into an area smaller than a pea. 52 00:06:42,367 --> 00:06:45,439 A black hole is gravity gone mad. 53 00:06:45,607 --> 00:06:47,996 Nothing can ever escape. 54 00:06:49,207 --> 00:06:51,596 What could create such a monster - 55 00:06:51,767 --> 00:06:54,839 something so heavy and yet unimaginably small? 56 00:06:58,927 --> 00:07:01,999 An event powerful enough to create a black hole 57 00:07:02,167 --> 00:07:05,239 should be visible right across the universe. 58 00:07:05,407 --> 00:07:09,525 And recently, we might actually have witnessed one as it happened. 59 00:07:10,407 --> 00:07:14,878 A team in Australia, headed by Professor Brian Boyle, spotted it. 60 00:07:15,047 --> 00:07:20,041 The first clue that led to his discovery came in the form of radiation - gamma rays - 61 00:07:20,207 --> 00:07:22,801 that are invisible to the human eye. 62 00:07:25,047 --> 00:07:29,723 The night sky that we can see with our own eyes is only part of the picture. 63 00:07:29,887 --> 00:07:32,845 Light comes to us in many different forms, 64 00:07:33,007 --> 00:07:37,797 from low-energy radio waves to the highest energy form of light: 65 00:07:37,967 --> 00:07:41,880 the gamma rays, the form of light that packs the biggest punch. 66 00:07:46,887 --> 00:07:51,403 Every night, in the gamma-ray sky, is fireworks night. 67 00:07:54,927 --> 00:07:58,761 We've been detecting violent bursts of gamma rays for decades, 68 00:07:58,927 --> 00:08:02,078 but we've never actually seen what causes them. 69 00:08:02,247 --> 00:08:05,284 It has to be a violent event, but what kind? 70 00:08:10,807 --> 00:08:14,800 The problem is, gamma-ray bursts only last a few seconds. 71 00:08:16,127 --> 00:08:20,803 And to make things harder, the best way to detect them is from space. 72 00:08:24,327 --> 00:08:26,966 (MAN) Gamma Ray Observatory to Atlantis... 73 00:08:27,127 --> 00:08:31,120 (WOMAN) Houston, no need to respond... 74 00:08:32,287 --> 00:08:35,279 (MAN 2) ..This gorgeous spacecraft... 75 00:08:35,447 --> 00:08:38,519 During a routine observation, the Gamma Ray Observatory 76 00:08:38,687 --> 00:08:42,805 detected an enormous blast of energy going off in deep space. 77 00:08:57,327 --> 00:08:59,397 What had triggered it? 78 00:08:59,567 --> 00:09:02,764 Brian Boyle's team, guided by the space observatory, 79 00:09:02,927 --> 00:09:06,124 turned their ground-based optical telescopes on to the blast 80 00:09:06,287 --> 00:09:09,518 in the hope of seeing it before it faded. 81 00:09:17,567 --> 00:09:20,843 (BOYLE) The information was really down to the ground. 82 00:09:21,007 --> 00:09:23,646 The optical telescopes sprang into action, 83 00:09:23,807 --> 00:09:27,959 to try to localise where this burst of energy had come from. 84 00:09:30,847 --> 00:09:33,964 What we found was something we didn't expect, 85 00:09:34,127 --> 00:09:37,278 that this light was actually coming from a supernova. 86 00:09:43,327 --> 00:09:47,764 What they'd seen with their telescopes was an exploding star. 87 00:09:53,007 --> 00:09:57,319 But the explosion was far larger than anyone had ever witnessed before. 88 00:09:59,967 --> 00:10:02,197 (EXPLOSION) 89 00:10:05,727 --> 00:10:08,605 And in the heart of that cataclysmic explosion, 90 00:10:08,767 --> 00:10:13,636 the researchers realised that something astonishing and terrifying had happened. 91 00:10:13,807 --> 00:10:17,720 As the massive star died, a monster had been born. 92 00:10:19,247 --> 00:10:21,556 We'd witnessed the birth of a black hole. 93 00:10:28,527 --> 00:10:31,599 What Boyle's team had seen was the death of a star so heavy 94 00:10:31,767 --> 00:10:38,002 that when it exploded, its mass collapsed inwards instead of blasting out into space. 95 00:10:47,247 --> 00:10:50,683 This star is absolutely huge. 96 00:10:53,727 --> 00:10:58,164 It's a hundred times bigger than our sun and thousands of times brighter. 97 00:11:02,887 --> 00:11:05,082 (EXPLOSION) 98 00:11:15,807 --> 00:11:18,116 But it doesn't just explode. 99 00:11:18,287 --> 00:11:22,644 As its surface layer blasts upwards, its core is smashed inwards. 100 00:11:28,767 --> 00:11:31,486 The centre of the star collapses in on itself, 101 00:11:31,647 --> 00:11:35,925 billions of tonnes of star stuff crushed smaller and smaller, 102 00:11:36,087 --> 00:11:40,478 until the whole star is squeezed to a single microscopic point. 103 00:11:47,247 --> 00:11:53,083 And from the remains of the dying star, a black hole is born. 104 00:12:04,727 --> 00:12:07,002 In our galaxy, a massive star explodes 105 00:12:07,167 --> 00:12:10,364 and creates a new black hole every 1,000 years - 106 00:12:10,567 --> 00:12:12,956 which may not sound like a lot, 107 00:12:13,127 --> 00:12:17,279 until you remember that the galaxy has been here a very long time. 108 00:12:19,247 --> 00:12:24,719 Speeding up its history, you can see that stars have been going off like firecrackers. 109 00:12:24,887 --> 00:12:27,481 And when a black hole is born, it never dies. 110 00:12:27,647 --> 00:12:30,878 Every hole that was ever created is still out there, 111 00:12:31,047 --> 00:12:34,562 so there should be around ten million of them, somewhere. 112 00:12:34,727 --> 00:12:36,843 The question is - where? 113 00:12:46,807 --> 00:12:52,404 Until recently, black holes remained unseen in the depths of space. 114 00:12:52,567 --> 00:12:57,004 But something as deadly as a black hole can't remain hidden forever. 115 00:12:59,687 --> 00:13:03,600 Like most predators, they leave a trail of destruction. 116 00:13:09,727 --> 00:13:13,845 And scientists are now beginning to recognise these telltale signs. 117 00:13:14,007 --> 00:13:17,556 One black hole hunter is Janna Levin. 118 00:13:20,367 --> 00:13:24,406 Even though black holes are invisible, it doesn't mean they have no effects. 119 00:13:24,567 --> 00:13:27,161 They're extremely strong vortices 120 00:13:27,327 --> 00:13:32,003 and pull matter in these swirling winds around them, a lot like a tornado. 121 00:13:35,367 --> 00:13:39,804 And like a tornado, you might not see it until the debris gets sucked up, 122 00:13:39,967 --> 00:13:43,084 like THIS tornado is now pulling the gases in it. 123 00:13:43,247 --> 00:13:47,718 So suddenly you can see the presence of this vortex, this strong swirling wind. 124 00:13:55,167 --> 00:14:00,480 It isn't the wind of a tornado you see - it's the havoc it creates. 125 00:14:01,447 --> 00:14:03,802 (EMERGENCY VEHICLE SIRENS) 126 00:14:11,567 --> 00:14:16,004 That's how we detect black holes, too - by the damage they do. 127 00:14:17,087 --> 00:14:20,602 (LEVIN) Tornados are incredibly powerful, but you don't SEE them 128 00:14:20,767 --> 00:14:25,238 until they suck stuff into them, until you see them pulling up houses and cars, 129 00:14:25,407 --> 00:14:29,400 and gas and smoke and clouds. It's the same with black holes. 130 00:14:29,567 --> 00:14:33,196 You don't see them until they pull in the matter around them. 131 00:14:41,247 --> 00:14:43,807 This is what astronomers look for. 132 00:14:47,007 --> 00:14:49,362 Not the black hole itself, 133 00:14:49,527 --> 00:14:53,566 but stars caught in the black hole's incredible gravitational pull. 134 00:15:00,007 --> 00:15:04,523 This one is tearing apart a star that drifted too close. 135 00:15:12,127 --> 00:15:15,642 A feeding black hole is anything but black. 136 00:15:27,327 --> 00:15:31,525 The whole star is wrenched out of shape as the monster tugs at it. 137 00:15:44,287 --> 00:15:47,245 Gas from the star whirls around the hole. 138 00:15:47,407 --> 00:15:51,878 It forms a super-hot disc of star debris, 100,000 km across. 139 00:15:55,287 --> 00:15:58,723 It's a deadly embrace that will last millions of years. 140 00:16:03,207 --> 00:16:07,166 And what the black hole can't swallow, it belches out. 141 00:16:10,247 --> 00:16:14,957 Huge jets of uneaten star are spat out into space. 142 00:16:25,967 --> 00:16:28,959 Some of the most spectacular black holes we've seen 143 00:16:29,127 --> 00:16:32,483 are SO powerful and spinning SO rapidly 144 00:16:32,647 --> 00:16:36,686 that they create these huge jets, these powerful funnels of material. 145 00:16:43,927 --> 00:16:49,160 They're thin but incredibly, incredibly long, incredibly vast. 146 00:16:51,807 --> 00:16:57,245 And the jets themselves can cross an entire galaxy. They're absolutely huge. 147 00:17:06,407 --> 00:17:11,606 The damage a black hole inflicts on a star can be seen clear across the universe. 148 00:17:23,327 --> 00:17:29,163 Once astronomers knew what to look for, they began to hunt for feeding black holes. 149 00:17:32,647 --> 00:17:37,482 Using powerful space telescopes, we've tracked down more and more of them. 150 00:17:37,647 --> 00:17:43,085 And these are the actual images - black holes tearing apart everything they meet. 151 00:17:53,247 --> 00:17:57,286 Most of them are remote. They're in distant corners of the universe. 152 00:17:57,447 --> 00:18:01,122 And we've only found them BECAUSE they're feeding. 153 00:18:01,287 --> 00:18:04,324 But what about the ones that aren't feeding? 154 00:18:04,487 --> 00:18:09,845 Where are the millions of black holes that should be wandering through OUR galaxy? 155 00:18:20,687 --> 00:18:24,566 They remain hidden against the dark background of space. 156 00:18:33,767 --> 00:18:38,283 Luckily, there is a way of tracking even the blackest of black holes. 157 00:18:39,647 --> 00:18:44,277 And THIS is what gives them away - light. 158 00:18:45,807 --> 00:18:49,561 A black hole's powerful gravity affects everything around it. 159 00:18:49,727 --> 00:18:51,797 It can even bend light. 160 00:18:53,487 --> 00:18:59,198 So when a black hole passes in front of a star, the light from that star is distorted... 161 00:19:02,087 --> 00:19:05,079 ..and the black hole gives itself away. 162 00:19:12,367 --> 00:19:17,919 Finding a star at the precise moment it's distorted by a black hole is a daunting task. 163 00:19:20,687 --> 00:19:26,398 But that didn't stop one very, very patient astronomer from trying to see the invisible. 164 00:19:31,967 --> 00:19:35,323 Tim Axelrod has dedicated many years of his life 165 00:19:35,487 --> 00:19:38,604 to the pursuit of the universe's hidden objects. 166 00:19:42,807 --> 00:19:47,756 For eight years, we've been looking at the same patch of sky, 167 00:19:47,927 --> 00:19:50,805 monitoring the brightness of 20 million stars. 168 00:20:01,567 --> 00:20:07,278 We're looking for micro-lensing events. These events are extremely rare. 169 00:20:07,447 --> 00:20:12,123 They occur when a massive object passes across our line of sight to a distant star. 170 00:20:14,287 --> 00:20:20,601 Axelrod set about his search for what he calls "gravitational micro-lensing" - 171 00:20:20,767 --> 00:20:25,841 when a star's light is distorted by a massive object like a black hole. 172 00:20:34,687 --> 00:20:37,326 But the odds were stacked against him. 173 00:20:37,487 --> 00:20:40,957 At best, his chance of finding the right star was one in a million. 174 00:20:43,847 --> 00:20:46,725 That factor seemed impossibly large, 175 00:20:46,887 --> 00:20:50,243 so most people thought we would fail pretty dismally. 176 00:20:55,287 --> 00:20:59,997 Undaunted by the enormity of the task and the scepticism of his colleagues, 177 00:21:00,167 --> 00:21:05,844 Axelrod set about looking for that one telltale pinprick of light amongst 20 million stars, 178 00:21:06,007 --> 00:21:08,919 every night for eight entire years. 179 00:21:13,367 --> 00:21:16,757 Then, one night, he hit the jackpot. 180 00:21:19,887 --> 00:21:23,163 This is a view of the Large Magellanic Cloud. 181 00:21:23,327 --> 00:21:27,639 The blue square shows the field of view of our telescope. 182 00:21:29,127 --> 00:21:32,483 Now we've zoomed in a bit. The star we're interested in 183 00:21:32,647 --> 00:21:37,641 is a pretty inconspicuous fellow right in the centre of the cross here. 184 00:21:37,807 --> 00:21:42,323 Now we zoom in yet again. This is picking the needle out of the haystack. 185 00:21:42,487 --> 00:21:48,403 And what we saw when we looked at it over a period of time was this. 186 00:21:54,007 --> 00:21:56,396 We were, naturally, ecstatic. 187 00:21:56,567 --> 00:22:01,516 Everyone that saw it agreed immediately that this was gravitational micro-lensing, 188 00:22:01,687 --> 00:22:04,247 so we were just over the moon. 189 00:22:05,327 --> 00:22:08,399 Far out in space, he had seen the impossible. 190 00:22:08,567 --> 00:22:14,915 A massively heavy object like a black hole, sliding silently in front of a distant star. 191 00:22:28,287 --> 00:22:33,520 Next, Axelrod turned to our own galaxy. What he saw was disturbing - 192 00:22:33,687 --> 00:22:37,202 evidence not of one or two black holes, 193 00:22:37,367 --> 00:22:39,358 but hundreds. 194 00:22:45,887 --> 00:22:49,084 But is that anything for us here on Earth to worry about? 195 00:22:49,247 --> 00:22:53,320 Could our own fragile planet ever encounter one of these invisible monsters? 196 00:22:58,967 --> 00:23:03,563 If we do ever meet a black hole, it would tear our world to shreds. 197 00:23:03,727 --> 00:23:09,518 But one thing is sure - our skies seem to be full of them. 198 00:23:11,047 --> 00:23:14,676 And our galaxy still has one last dark secret, 199 00:23:14,847 --> 00:23:19,921 and it took the most powerful telescope in the world to unlock it - the Keck in Hawaii. 200 00:23:20,087 --> 00:23:23,762 One of the astronomers using it is Andrea Ghez. 201 00:23:24,727 --> 00:23:27,924 The Keck telescope is a fabulous telescope to use. 202 00:23:28,087 --> 00:23:32,126 It's great because it's large. This is a case where bigger IS better. 203 00:23:32,287 --> 00:23:37,520 You can collect a lot of photons, so you can see very faint things and very fine detail. 204 00:23:38,927 --> 00:23:43,842 The telescope's vast mirror allows Andrea Ghez to study the centre of our galaxy 205 00:23:44,007 --> 00:23:46,805 with more accuracy than ever before. 206 00:23:50,487 --> 00:23:56,437 What astronomers have seen is a black hole a million times more powerful than normal. 207 00:23:57,287 --> 00:24:01,121 (GHEZ) Here's an example of an image we got just last night. 208 00:24:01,287 --> 00:24:07,237 We see that there are fainter stars towards the centre. These stars are very important. 209 00:24:07,407 --> 00:24:11,923 It's the motion of these stars that reveal the presence of the black hole. 210 00:24:22,247 --> 00:24:26,798 There is a black hole at the centre of our galaxy that is SO powerful 211 00:24:26,967 --> 00:24:31,358 that it spins whole stars around itself at impossible speeds. 212 00:24:31,527 --> 00:24:34,917 The fact that they're going 1,000 km per second 213 00:24:35,087 --> 00:24:40,207 tells us there's two million times the mass of the sun of matter there. 214 00:24:46,487 --> 00:24:49,081 This is no ordinary black hole. 215 00:24:49,247 --> 00:24:53,923 This black hole is a giant, two million times as heavy as our sun. 216 00:24:58,887 --> 00:25:02,197 And it's not in some far-flung region of the universe. 217 00:25:02,367 --> 00:25:06,963 This black hole is sitting right at the centre of OUR galaxy. 218 00:25:24,727 --> 00:25:29,596 Suddenly the idea that the Earth might one day fall victim to a black hole 219 00:25:29,767 --> 00:25:32,361 doesn't seem quite so unlikely. 220 00:25:36,247 --> 00:25:41,275 If we ARE ever unlucky enough to meet one, what would it be like? 221 00:25:46,287 --> 00:25:50,519 It begins far out in space, beyond the furthest planets. 222 00:25:50,687 --> 00:25:55,920 A black hole ploughs into the cloud of comets that surrounds our solar system 223 00:25:56,087 --> 00:25:59,124 and flings them towards Earth with incredible force. 224 00:25:59,287 --> 00:26:01,562 (WHOOSHING) 225 00:26:06,727 --> 00:26:08,718 (EXPLOSION) 226 00:26:08,887 --> 00:26:12,357 These impacts are the first warning of our fate. 227 00:26:19,807 --> 00:26:23,516 As the black hole comes closer, its next victim is Jupiter, 228 00:26:23,687 --> 00:26:26,724 the giant of our solar system. 229 00:26:39,287 --> 00:26:44,566 Even from so far away, the black hole's gravity makes itself felt here on Earth. 230 00:26:44,727 --> 00:26:47,400 Our world is being shaken apart. 231 00:26:55,167 --> 00:26:57,920 But the black hole hasn't finished yet. 232 00:26:58,087 --> 00:27:02,478 It's heading straight for the heart of the solar system, our sun. 233 00:27:07,247 --> 00:27:11,763 Though tiny in comparison, it tears the sun apart. 234 00:27:19,207 --> 00:27:23,962 Dragging the sun with it, the black hole heads towards Earth. 235 00:27:32,327 --> 00:27:35,558 The Earth is now unbearably close to the sun. 236 00:27:37,167 --> 00:27:40,477 All life has long since ceased to exist. 237 00:27:44,327 --> 00:27:47,478 And our planet starts to melt. 238 00:27:51,207 --> 00:27:56,645 Quietly, our battered world disintegrates, and is consumed. 239 00:28:01,367 --> 00:28:06,885 And all that is left is the black hole, drifting through space. 240 00:28:12,647 --> 00:28:15,844 Earth eaten by a black hole? It sounds bizarre. 241 00:28:16,007 --> 00:28:19,283 But we know there are millions of these monsters out there. 242 00:28:19,447 --> 00:28:21,756 What we don't know, is...