WEBVTT 00:00:04.041 --> 00:00:06.801 Neil Armstrong: I can see everything quite clear! Y. 00:00:07.961 --> 00:00:10.401 It has a stark beauty all its own. 00:00:19.201 --> 00:00:20.921 B uzz a ld ri n: Magnificent desolation. 00:00:22.601 --> 00:00:25.001 - Beautiful view. - Armstro n g: Isn't that something? 00:00:43.801 --> 00:00:46.121 Brian Cox: The milky way seems a tranquil place... 00:00:51.641 --> 00:00:57.121 Hundreds of billions of stars serenely spinning through the cosmos. 00:01:02.641 --> 00:01:06.561 But journey in wards through the gas and dust 00:01:06.641 --> 00:01:08.961 that shrouds the galactic core, 00:01:13.041 --> 00:01:15.081 and you 'd see a curious sight... 00:01:20.961 --> 00:01:25.641 Stars orbiting seemingly empty space. 00:01:29.241 --> 00:01:32.681 Something dark and ancient lives here... 00:01:34.561 --> 00:01:37.881 A hole in the fabric of the universe. 00:02:04.721 --> 00:02:07.881 Every one of those points of light in the night sky 00:02:07.961 --> 00:02:10.361 is a strange and fascinating place. 00:02:12.361 --> 00:02:15.921 Magnificent suns with countless planets orbiting around them, 00:02:16.001 --> 00:02:19.321 alien worlds beyond imagination. 00:02:19.401 --> 00:02:24.041 But the strangest and most fascinating places out there, by far, 00:02:24.121 --> 00:02:26.441 are dark and unseen. 00:02:36.081 --> 00:02:39.841 An in visible monster is lurking in the centre of the milky way, 00:02:48.241 --> 00:02:52.121 A monster that drains the colour from the universe, 00:02:56.521 --> 00:02:58.881 with the power to destroy worlds, 00:03:03.961 --> 00:03:06.161 And stop time. 00:03:24.241 --> 00:03:27.641 We've named the monster sagittarius a I 00:03:28.721 --> 00:03:31.321 and we believe it to be a black hole. 00:03:37.801 --> 00:03:43.201 Sagittarius a has played a major role in the evolution of our galaxy 00:03:43.281 --> 00:03:44.561 and may even have influenced 00:03:44.641 --> 00:03:47.841 the formation of stars and planets like ours. 00:03:48.521 --> 00:03:53.721 But there is so much more. Because black holes like sagittarius a 00:03:53.801 --> 00:03:57.241 Present the most profound intellectual challenge. 00:03:58.041 --> 00:04:01.561 They are part of nature, just like you and me. 00:04:01.681 --> 00:04:04.201 So, we should be able to understand them. 00:04:04.281 --> 00:04:07.961 But they are holes in the fabric of the universe. 00:04:08.041 --> 00:04:13.401 They are gra vita tional prisons from which even light itself can't escape. 00:04:13.921 --> 00:04:17.401 But in trying to understand them, physicists have been led 00:04:17.481 --> 00:04:22.641 to completely reassess our most basic understanding of reality. 00:04:25.961 --> 00:04:29.143 But there are answers hiding in the void 00:04:29.167 --> 00:04:32.201 for those brave enough to seek them. 00:05:16.241 --> 00:05:18.361 Eileen Collins: And we copy at go for deploy. 00:05:24.841 --> 00:05:26.601 You look out and this thing is so big, 00:05:26.681 --> 00:05:29.961 you certainly know that it's moving over the head of the shuttle. 00:05:32.201 --> 00:05:34.001 Cox: In the summer of 7999, 00:05:34.361 --> 00:05:37.561 NASA's flagship mission for x -ra y astronomy 00:05:37.641 --> 00:05:40.121 was released from the shuttle cargo bay. 00:05:44.961 --> 00:05:46.841 Collins: There is nothing as beautiful 00:05:46.921 --> 00:05:49.521 as chandra sailing off on its way to work. 00:05:55.041 --> 00:05:58.641 Cox: High above the earth, chandra scanned the sky 00:06:00.001 --> 00:06:02.801 hunting for some of the hottest regions in the universe, 00:06:05.001 --> 00:06:08.401 exploding stars and clusters of galaxies. 00:06:18.201 --> 00:06:21.001 But on September 74, 2073, 00:06:21.481 --> 00:06:26.201 after 74 years, chandra chanced on something else entirely. 00:06:35.121 --> 00:06:39.241 The telescope gazed into the constellation of sagittarius, 00:06:39.321 --> 00:06:42.161 hoping to observe a large cloud of hot gas. 00:06:57.041 --> 00:07:02.401 Instead, it recorded a flash of x—ra ys, just a few pixels across, 00:07:04.801 --> 00:07:09.201 coming from the apparently empty space in the galactic core. 00:07:16.441 --> 00:07:21.921 Something had got very hot for a very short period of time. 00:07:34.281 --> 00:07:37.361 It's thought that the flash seen by chandra 00:07:37.441 --> 00:07:41.561 may have been an asteroid tens of kilometres across, 00:07:56.281 --> 00:08:00.081 Ripped apart and burning up in a fireball 00:08:00.161 --> 00:08:03.441 300 times brighter than the sun. 00:08:11.441 --> 00:08:15.361 The culprit, sagittarius a "I 00:08:22.321 --> 00:08:26.161 The asteroid's destruction was our galaxy's black hole 00:08:26.961 --> 00:08:29.641 signalling its presence to the world. 00:08:44.321 --> 00:08:47.201 Twenty years ago, we didn't know for sure 00:08:47.281 --> 00:08:49.921 that there is a black hole at the centre of our galaxy. 00:08:50.321 --> 00:08:54.321 But by measuring bursts of radiation and observing in detail 00:08:54.401 --> 00:08:57.361 the orbits of stars close to the galactic centre, 00:08:57.441 --> 00:09:02.161 we now know that sagittarius a definitely exists, 00:09:02.241 --> 00:09:04.801 and we've been able to measure its mass. 00:09:04.881 --> 00:09:08.801 It is around four million times the mass of our sun, 00:09:08.881 --> 00:09:11.161 which makes it a supermassive black hole, 00:09:11.241 --> 00:09:15.921 one of the strangest and most powerful objects in the universe. 00:09:16.441 --> 00:09:20.361 And we've begun to suspect that sagittarius a isn'tjust 00:09:20.441 --> 00:09:22.241 some strange thing that sits 00:09:22.321 --> 00:09:25.721 tens of thousands of light years from earth, at the centre of the galaxy. 00:09:26.321 --> 00:09:30.961 It has played a crucial role in the evolution of the milky way, 00:09:31.041 --> 00:09:36.161 and the whole story began with the death of one massive star. 00:09:53.681 --> 00:09:55.521 Soon after the dawn of time, 00:09:59.241 --> 00:10:01.961 the cosmos was home to colossal stars, 00:10:07.921 --> 00:10:10.801 Hundreds of times more massive than the sun, 00:10:13.081 --> 00:10:17.041 stars that burnt blue in intense heat. 00:10:24.001 --> 00:10:27.121 But the brightest stars are the shortest lived. 00:10:34.521 --> 00:10:37.721 One lived a particularly fast and furious life, 00:10:41.401 --> 00:10:45.201 burning through its nuclear fuel in just a few million years. 00:10:56.841 --> 00:11:01.201 And with nothing left in the tank, gravity took over. 00:11:02.761 --> 00:11:04.721 The star collapsed... 00:11:06.001 --> 00:11:09.361 E ver smaller, e ver denser... 00:11:12.121 --> 00:11:14.401 Until it seemingly disappeared. 00:11:16.161 --> 00:11:20.561 The remnants of the star, now smaller than an atom, 00:11:21.681 --> 00:11:23.721 lost from the universe. 00:11:25.521 --> 00:11:28.841 All that's left is a ghost, 00:11:30.161 --> 00:11:31.721 a black hole. 00:11:42.401 --> 00:11:47.881 The Genesis of sagittarius a wasn't some bizarre one-off event. 00:11:49.161 --> 00:11:52.801 It's possible that almost all early stars 00:11:52.881 --> 00:11:55.161 became black holes when they died. 00:11:57.401 --> 00:12:02.521 Black holes are simply what happens when gravity goes unchecked, 00:12:03.561 --> 00:12:08.481 compacting matters so densely it tears a hole in the universe. 00:12:11.761 --> 00:12:13.281 In the vicinity of a black hole, 00:12:13.361 --> 00:12:17.681 space and time behave in very counter-intuitive ways. 00:12:18.081 --> 00:12:23.241 In fact, this river provides a beautiful and surprisingly accurate analogy. 00:12:23.321 --> 00:12:26.761 See, close to a black hole, you can think of space itself 00:12:26.841 --> 00:12:29.761 as flowing towards the black hole. 00:12:33.801 --> 00:12:37.601 Now, here, the flow is not too fast. 00:12:37.681 --> 00:12:39.841 And so, you can imagine I can jump into that river, 00:12:39.921 --> 00:12:43.121 I can swim faster than the river of space. 00:12:43.201 --> 00:12:45.761 And so, I can escape out into the galaxy. 00:12:46.481 --> 00:12:48.561 But as you get closer to the black hole, 00:12:48.641 --> 00:12:53.121 the river of space flows faster and faster and faster. 00:12:57.761 --> 00:13:02.001 A collapsed star is so small and yet so massive 00:13:02.561 --> 00:13:06.841 that, close to it, the gravitational forces become overwhelming. 00:13:32.481 --> 00:13:37.881 There is no limit to the speed at which the river of space can flow. 00:13:53.161 --> 00:13:56.201 There's a place where the river becomes a waterfall, 00:13:56.281 --> 00:14:00.681 where no matter how fast I swim, I could never escape upstream. 00:14:00.761 --> 00:14:03.601 And that's what happens in the vicinity of a black hole. 00:14:06.961 --> 00:14:12.601 The river of space flows at, and then, faster than the speed of light. 00:14:12.681 --> 00:14:16.601 Light itself can't move fast enough to escape. 00:14:20.321 --> 00:14:23.001 And that's what sagittarius a is. 00:14:23.561 --> 00:14:26.801 It's a waterfall in the fabric of the universe. 00:14:38.161 --> 00:14:40.401 From the moment the black hole formed 00:14:41.281 --> 00:14:45.961 the seed of sagittarius a had a heart of pure darkness, 00:14:50.401 --> 00:14:54.201 the interior forever hidden from view, 00:14:54.281 --> 00:14:58.281 shielded from the rest of the universe by a boundary in space... 00:15:00.441 --> 00:15:02.201 The event horizon, 00:15:03.641 --> 00:15:05.681 the ultimate point of no return. 00:15:12.401 --> 00:15:16.761 As we approach the event horizon, we get our first glimpse 00:15:16.841 --> 00:15:20.001 of the true weirdness of black holes. 00:15:32.441 --> 00:15:36.201 Einstein taught us that space and time are not what they seem. 00:15:36.761 --> 00:15:41.161 They are merged together into a kind of a fabric, the fabric of the universe. 00:15:41.281 --> 00:15:43.041 It's called spacetime. 00:15:43.121 --> 00:15:46.921 And Einstein also taught us that the presence of massive objects, 00:15:47.001 --> 00:15:48.921 stars, and planets, and galaxies, 00:15:49.001 --> 00:15:53.081 curve and distort the fabric of the universe, 00:15:53.161 --> 00:15:55.841 and that's what we feel as the force of gravity. 00:16:08.241 --> 00:16:13.601 But that distortion is not only in space, it's also in time. 00:16:16.481 --> 00:16:19.641 As you go closer and closer to a massive object, 00:16:19.721 --> 00:16:22.361 the rate that time passes slows down. 00:16:22.961 --> 00:16:25.481 So, if I look towards a black hole, 00:16:25.561 --> 00:16:30.121 I see time passing slower and slower and slower 00:16:30.201 --> 00:16:35.201 until on the event horizon, time stops. 00:17:18.561 --> 00:17:24.081 Sagittarius a was born a waterfall in the fabric of the universe, 00:17:25.681 --> 00:17:31.881 where space flows faster than light and time grinds to a halt. 00:17:41.881 --> 00:17:44.521 But our black hole was still just a baby, 00:17:48.681 --> 00:17:50.721 dwarfed by the stars around it. 00:17:51.721 --> 00:17:55.441 It was nothing like the monster it would become. 00:18:05.641 --> 00:18:11.161 Sagittarius a today is four million times the mass of the sun. 00:18:11.281 --> 00:18:13.801 There has never been a star that massive. 00:18:14.161 --> 00:18:18.521 So, it must have formed by the collapse of something much smaller, 00:18:18.961 --> 00:18:22.481 and then, it must have grown over the lifetime of the milky way 00:18:22.561 --> 00:18:23.601 by eating stuff. 00:18:24.241 --> 00:18:28.681 And fortunately, there has been a lot of stuff around for it to eat. 00:18:32.481 --> 00:18:36.321 The young black hole's inexorable gravitational pull 00:18:36.401 --> 00:18:40.121 meant there was no escape for anything that strayed too close. 00:18:56.881 --> 00:19:03.201 Sagittarius a began to grow, pulling on nearby stars... 00:19:07.681 --> 00:19:12.841 Before ripping them to shreds and feasting on hot plasma, 00:19:19.401 --> 00:19:25.521 The black hole gaining more mass and more gravitational power. 00:19:31.001 --> 00:19:34.561 But we don't think there were enough stars nearby 00:19:34.641 --> 00:19:39.161 for the black hole to grow supermassive on a diet of stars alone. 00:19:42.921 --> 00:19:46.921 Instead, it developed a taste for more massive prey. 00:20:10.401 --> 00:20:14.601 When another black hole passed close to sagittarius a'fi 00:20:14.681 --> 00:20:17.721 they became locked in a gravitational embrace... 00:20:25.841 --> 00:20:30.681 Spiralling towards each other, approaching half the speed of light... 00:20:37.201 --> 00:20:38.761 Before colliding. 00:20:47.161 --> 00:20:50.721 Sagittarius a cannibalised its cousin, 00:20:53.441 --> 00:20:57.081 creating ripples in the fabric of the universe itself. 00:21:03.881 --> 00:21:05.641 More meals were to follow. 00:21:06.481 --> 00:21:10.001 Black holes, stars, gas clouds, 00:21:10.081 --> 00:21:13.841 whatever ventured too deep into its lair. 00:21:17.601 --> 00:21:21.041 And as our black hole's power and influence grew, 00:21:24.321 --> 00:21:26.521 its surroundings were changing, too. 00:21:29.481 --> 00:21:34.841 Around the galactic core, hundreds of billions of stars were in orbit, 00:21:38.841 --> 00:21:43.441 slowly spinning around their common centre of mass, 00:21:47.281 --> 00:21:51.441 evolving into the familiar spiralling disk... 00:21:54.801 --> 00:21:57.761 The majestic milky way, 00:21:57.841 --> 00:22:02.161 with sagittarius a at its core. 00:22:15.001 --> 00:22:19.801 Sagittarius a became what we now call a supermassive black hole. 00:22:19.881 --> 00:22:23.361 Many tens or even hundreds of thousands of times more massive 00:22:23.441 --> 00:22:25.561 than any star in the universe. 00:22:26.081 --> 00:22:28.721 And sagittarius a is not unique. 00:22:28.801 --> 00:22:31.761 We now think that virtually every large galaxy 00:22:31.841 --> 00:22:34.801 has a supermassive black hole at its heart. 00:22:48.961 --> 00:22:51.841 Chandra has looked beyond the milky way 00:22:51.921 --> 00:22:55.081 and observed countless supermassive black holes, 00:22:55.161 --> 00:23:00.321 lurking at the hearts of the myriad galaxies that litter the cosmos. 00:23:07.041 --> 00:23:10.881 These monsters aren 't obscure quirks of nature. 00:23:11.801 --> 00:23:14.601 They are fundamental features of it... 00:23:18.321 --> 00:23:20.561 And far from being bit players. 00:23:21.201 --> 00:23:22.801 We 're starting to realise that 00:23:22.881 --> 00:23:28.481 black holes have the power and reach to sculpt the galaxies around them. 00:23:44.081 --> 00:23:48.081 The centre of our young galaxy was rich in gas and dust, 00:23:50.441 --> 00:23:52.721 more offerings to feast on. 00:24:03.561 --> 00:24:05.321 This was a gluttonous period 00:24:06.361 --> 00:24:10.361 that marked a new era for the milky way's supermassive black hole 00:24:13.361 --> 00:24:18.881 when the in visible monster became sculptor of the galaxy. 00:24:37.801 --> 00:24:41.641 Creation and destruction often go hand in hand in the universe, 00:24:41.721 --> 00:24:43.361 and black holes are no exception. 00:24:43.441 --> 00:24:48.281 Sagittarius a is certainly not only an agent of destruction 00:24:48.361 --> 00:24:52.081 because the material that falls inwards towards the black hole 00:24:52.161 --> 00:24:54.721 doesn't all vanish across the event horizon. 00:24:55.201 --> 00:24:58.161 A lot of it goes into orbit around the black hole. 00:25:01.841 --> 00:25:04.521 And that region is tremendously violent. 00:25:04.601 --> 00:25:07.281 There are magnetic fields that swirl around 00:25:07.361 --> 00:25:12.121 and become twisted and distorted, and they can throw material out 00:25:12.201 --> 00:25:14.481 along the magnetic Poles of the black hole, 00:25:14.561 --> 00:25:18.121 making jets that sweep through the galaxy. 00:25:23.041 --> 00:25:25.121 It's only recently that we've grasped 00:25:25.201 --> 00:25:29.001 the true scale of sagittarius a 's eruptions. 00:25:34.841 --> 00:25:35.841 Man: Engine start. 00:25:37.641 --> 00:25:41.081 One, zero. Lift-off. 00:25:45.841 --> 00:25:49.161 The delta rocket carrying a gamma ray telescope, 00:25:49.241 --> 00:25:52.921 searching for unseen physics in the stars of the galaxies. 00:26:04.841 --> 00:26:06.681 Cox: Just over a decade ago, 00:26:06.761 --> 00:26:10.041 a completely unexpected disco very was made, 00:26:10.121 --> 00:26:13.801 likened to finding a brand new continent here on earth. 00:26:23.921 --> 00:26:28.041 The fermi space telescope was built to detect gamma rays, 00:26:28.601 --> 00:26:31.561 the most energetic radiation in the universe. 00:26:46.241 --> 00:26:50.481 As fermi orbited the earth, it constructed a map of the sky... 00:27:01.481 --> 00:27:05.481 And saw emerging from the plane of the milky way, 00:27:10.241 --> 00:27:17.201 two colossal bubbles of material, each 25, 000 light years across. 00:27:26.561 --> 00:27:29.361 These bubbles are superheated gas. 00:27:30.521 --> 00:27:34.801 If our eyes were sensitive to the wavelengths of light emitted by those bubbles, 00:27:34.881 --> 00:27:39.121 they would span half the sky as seen from here on earth. 00:27:39.921 --> 00:27:43.081 And they point back to the centre of the galaxy. 00:27:43.161 --> 00:27:46.921 It looks like their origin is sagittarius a . 00:27:47.001 --> 00:27:48.041 Think about that. 00:27:48.121 --> 00:27:52.561 I mean, sagittarius a is big but not big on a galactic scale. 00:27:52.641 --> 00:27:56.561 It would fit comfortably inside the orbit of Mercury, in our solar system. 00:28:01.281 --> 00:28:03.283 Though our black hole is only a fraction 00:28:03.307 --> 00:28:05.561 of the size of the galaxy around it, 00:28:07.641 --> 00:28:11.041 it had become sculptor of the milky way. 00:28:32.561 --> 00:28:34.201 Every few million years, 00:28:34.921 --> 00:28:38.401 the dense ring of material circling our black hole 00:28:43.921 --> 00:28:47.481 Was accelerated by twisting magnetic fields... 00:28:49.721 --> 00:28:53.241 Into fiery jets of superheated matter. 00:28:59.321 --> 00:29:01.441 Jets so powerful 00:29:01.521 --> 00:29:05.281 they stripped the atmospheres from any planets in their path, 00:29:15.081 --> 00:29:18.681 And radiation rendered every earth-like world 00:29:18.761 --> 00:29:22.601 within 7,000 light years uninhabitable. 00:29:36.561 --> 00:29:40.881 But such was the scale of sagittarius a 's outbursts 00:29:40.961 --> 00:29:43.921 that far, far out in the galaxy, 00:29:49.561 --> 00:29:50.721 Destruction... 00:29:52.841 --> 00:29:54.561 Turned to creation. 00:30:19.041 --> 00:30:22.601 If you're looking for reasons why life not only began here on earth 00:30:23.161 --> 00:30:28.001 but was able to prosper for the almost four billion years it took for it to evolve 00:30:28.081 --> 00:30:30.721 into the complex living world that we see today, 00:30:30.801 --> 00:30:34.001 then, it might seem a bit of a stretch to point to a supermassive black hole 00:30:34.081 --> 00:30:37.481 at the centre of our galaxy and say, "that's one of the reasons why." 00:30:38.081 --> 00:30:39.841 But we're now beginning to suspect 00:30:39.921 --> 00:30:44.161 that those great outpourings of energy from sagittarius a 00:30:44.241 --> 00:30:48.521 Played a crucial role in making this region of the galaxy, 00:30:48.601 --> 00:30:51.121 one in which life can flourish. 00:30:54.961 --> 00:30:58.841 Because the hot gas ejected by sagittarius a 00:30:59.961 --> 00:31:03.001 Had a calming effect on the galaxy. 00:31:03.081 --> 00:31:06.681 Now, you might think that a hot gas cloud would produce more stars. 00:31:06.761 --> 00:31:09.161 But, in fact, the opposite is true because hot means that 00:31:09.241 --> 00:31:12.521 everything's moving around very fast, and that makes it more difficult 00:31:12.601 --> 00:31:17.561 for gravity to grab hold of everything and collapse it to form stars. 00:31:17.641 --> 00:31:21.041 So, sagittarius a reduced the number of stars 00:31:21.121 --> 00:31:25.681 that formed in this region of the galaxy, and that's a good thing. 00:31:25.761 --> 00:31:27.881 I mean, imagine if there was some giant star 00:31:27.961 --> 00:31:32.401 that had formed close by that exploded in a supernova explosion. 00:31:32.481 --> 00:31:35.441 That would not be a good thing if you're an amoeba 00:31:35.521 --> 00:31:39.121 and you have designs, one day, on evolving into Einstein. 00:31:39.841 --> 00:31:43.641 So, sagittarius a turned what is potentially 00:31:43.721 --> 00:31:47.561 a violent region of our galaxy into a peaceful one. 00:31:55.241 --> 00:31:59.121 The warm gases pushed out by sagittarius a 00:31:59.201 --> 00:32:01.761 Slowed the rate of star formation. 00:32:08.561 --> 00:32:13.481 And around one small yellow star in a quiet region 00:32:13.561 --> 00:32:17.441 at the unfashionable end of the outer spiral arms of the galaxy, 00:32:29.881 --> 00:32:34.761 Four billion years of stability made all the difference. 00:32:56.481 --> 00:32:58.721 Now, of course, there are many things that are necessary 00:32:58.801 --> 00:33:00.561 for life to exist on a planet. 00:33:01.361 --> 00:33:06.481 The list is unimaginably vast, but I think it is interesting 00:33:06.561 --> 00:33:11.921 that on that list, there is the presence of this strange object, 00:33:12.001 --> 00:33:14.561 a black hole, sagittarius a, 00:33:14.641 --> 00:33:18.921 tens of thousands of light years away at the centre of our galaxy. 00:33:43.561 --> 00:33:48.921 Having cleared out much of the gas, dust and stars that once lay close by, 00:33:51.841 --> 00:33:53.721 there was little left to feast on. 00:33:57.081 --> 00:33:59.801 Our black hole fell silent. 00:34:04.761 --> 00:34:07.761 The enormous bubbles spotted by fermi... 00:34:09.281 --> 00:34:12.201 Echoes of a glorious past. 00:34:19.321 --> 00:34:24.001 Today, sagittarius a is a sleeping giant, 00:34:25.561 --> 00:34:30.441 a brooding beast operating on a slow simmer. 00:34:44.361 --> 00:34:48.401 Sagittarius a's journey from violent destroyer 00:34:48.481 --> 00:34:50.681 to sculptor of the galaxy 00:34:50.761 --> 00:34:52.801 to the sleeping giant that we see today 00:34:52.881 --> 00:34:57.441 has been pieced together over the last 20 years by observational data 00:34:57.521 --> 00:35:00.601 from telescopes such as chandra and fermi. 00:35:02.561 --> 00:35:04.841 But there's a very big difference indeed, 00:35:04.921 --> 00:35:06.401 between knowing how a black hole 00:35:06.481 --> 00:35:09.881 interacts with its environment, how it sculpts a galaxy 00:35:10.681 --> 00:35:14.241 and what it actually is at a deep level. 00:35:17.681 --> 00:35:20.361 What is it really like inside? 00:35:55.721 --> 00:35:59.641 Cox: It's by looking into the future that we 're beginning to explore 00:35:59.721 --> 00:36:02.321 the deep mystery of black holes. 00:36:07.681 --> 00:36:11.041 Dozens of stars orbit around sagittarius a I 00:36:12.681 --> 00:36:18.161 some passing just a few billion miles from the event horizon, 00:36:18.241 --> 00:36:21.481 a hair's breadth on galactic scales. 00:36:23.841 --> 00:36:26.921 These fl ybys could have fatal consequences. 00:36:40.961 --> 00:36:44.961 Some of these stars will likely have planets in orbit, 00:36:45.041 --> 00:36:48.801 planets that may stray too close to the beast, 00:36:57.881 --> 00:37:04.641 A math to a flame, pulled from its parent star towards the abyss. 00:37:18.041 --> 00:37:20.801 If the planet survives its journey inwards, 00:37:23.601 --> 00:37:28.361 and we could stand on its surface and look out into the universe beyond, 00:37:38.881 --> 00:37:44.041 We would see space and time becoming increasingly distorted. 00:38:07.281 --> 00:38:11.681 But eventually, tidal gravitational forces become too strong. 00:38:33.921 --> 00:38:37.681 Inexorabl y, the singularity awaits, 00:38:39.281 --> 00:38:44.281 the end of time where all paths terminate. 00:39:12.401 --> 00:39:18.081 Over trillions of years, all the stars around sagittarius a 00:39:18.161 --> 00:39:21.001 Will gradually fade and die. 00:39:26.681 --> 00:39:31.801 On more and more alien worlds, the dawn will fail to come. 00:39:41.721 --> 00:39:45.321 But our supermassive monster will go on, 00:39:46.641 --> 00:39:49.041 its secrets sealed away inside... 00:39:50.481 --> 00:39:52.921 Seemingly forever. 00:39:59.681 --> 00:40:02.241 We predict that, one day, 00:40:02.321 --> 00:40:06.481 black holes will be all that remains in the universe. 00:40:07.001 --> 00:40:09.081 The final dark age. 00:40:30.281 --> 00:40:33.361 If nothing can ever escape from black holes, 00:40:33.441 --> 00:40:37.401 if sagittarius a really is an eternal prison, 00:40:37.481 --> 00:40:40.641 then, this is the end of the story of the universe, 00:40:40.721 --> 00:40:44.241 darkness littered with holes in spacetime. 00:40:44.841 --> 00:40:47.441 But we don't think this is the end of the story. 00:40:52.481 --> 00:40:57.201 We now believe that even black holes die. 00:41:04.321 --> 00:41:07.641 And their deaths come at the hands of what might seem 00:41:07.721 --> 00:41:12.961 an inconsequential detail discovered almost five decades ago. 00:41:16.801 --> 00:41:22.161 In 1975, Stephen Hawking published a remarkable paper in which he showed 00:41:22.281 --> 00:41:25.201 that black holes are not completely black. 00:41:25.281 --> 00:41:28.441 They glow faintly. They have a temperature. 00:41:28.521 --> 00:41:33.201 And here's his beautiful equation for the temperature of a black hole. 00:41:37.961 --> 00:41:41.601 And you can see that there's something deep going on... 00:41:42.481 --> 00:41:46.281 Because this has got all of physics in it. 00:41:46.681 --> 00:41:49.201 This thing here, "h-bar", is planck's constant, 00:41:49.281 --> 00:41:52.201 that's to do with quantum mechanics, the subatomic world. 00:41:52.281 --> 00:41:56.201 5 the speed of light. "G" is the strength of gravity. 00:41:56.281 --> 00:41:58.801 This "kb" here is boltzmann's constant, 00:41:58.881 --> 00:42:02.561 that's to do with temperature and thermodynamics. 00:42:02.641 --> 00:42:05.161 And this "m" here is the mass of the black hole. 00:42:05.241 --> 00:42:07.921 It's even got circles because it's got a pi in it. 00:42:09.121 --> 00:42:13.961 Ha wking's conclusion proved to be irrefutable 00:42:14.041 --> 00:42:17.361 and the implications are huge. 00:42:17.961 --> 00:42:21.201 If something has a temperature, then it radiates. 00:42:21.281 --> 00:42:23.641 That's why if you put your hand near something that's hot, 00:42:23.721 --> 00:42:25.041 you can feel it. 00:42:25.121 --> 00:42:26.721 And so, over timescales that are 00:42:26.801 --> 00:42:29.601 billions and billions and billions and billions of times 00:42:29.681 --> 00:42:32.521 longer than the current age of the universe, 00:42:32.601 --> 00:42:37.401 sagittarius a will eventually evaporate away. 00:42:57.921 --> 00:43:04.601 Very gradually, Hawking radiation will erode sagittarius a "I. 00:43:08.201 --> 00:43:11.121 Smaller and smaller... 00:43:16.121 --> 00:43:20.041 Until many trillions and trillions of years into the future... 00:43:26.201 --> 00:43:28.001 In a final burst of light, 00:43:30.601 --> 00:43:33.441 our black hole will die. 00:43:34.841 --> 00:43:37.681 And then, there will be darkness... 00:43:39.121 --> 00:43:41.121 For all eternity. 00:43:48.121 --> 00:43:51.561 Now, you may say quite legitimately, "well, why do we care? 00:43:51.641 --> 00:43:54.881 "Why does it matter if black holes evaporate away sometime 00:43:54.961 --> 00:43:59.281 "in the far, far future of the universe? There'll be nobody around to see it." 00:44:00.001 --> 00:44:04.801 But the discovery that black holes evaporate raises what I think 00:44:04.881 --> 00:44:08.281 is the most profound question in the history of physics, 00:44:08.361 --> 00:44:11.761 certainly over the last 100 years, and that's no exaggeration. 00:44:12.321 --> 00:44:17.601 See, what happens if I set fire to this piece of paper... 00:44:19.281 --> 00:44:21.321 With Stephen Hawking's equation written on it? 00:44:21.401 --> 00:44:27.201 I cause it to evaporate away. Do I destroy everything? 00:44:27.281 --> 00:44:29.961 Do I remove every piece of information, 00:44:30.041 --> 00:44:33.761 including the equation, from the universe when it burns away? 00:44:54.081 --> 00:44:56.001 Well, the answer is, no. 00:44:56.081 --> 00:45:01.561 If I could collect every ash, every molecule of gas 00:45:01.641 --> 00:45:03.921 that burns off into the atmosphere, 00:45:04.001 --> 00:45:08.081 then, in principle, I could reconstruct the piece of paper, 00:45:08.161 --> 00:45:10.441 and everything it contains, 00:45:10.521 --> 00:45:13.681 every piece of information on this piece of paper 00:45:14.161 --> 00:45:16.721 including Stephen Hawking's equation. 00:45:18.841 --> 00:45:22.670 But can that be true for black holes, 00:45:22.694 --> 00:45:24.641 the ultimate gravitational prisons, 00:45:24.721 --> 00:45:30.321 these objects in the sky from which even light itself can't escape? 00:45:31.121 --> 00:45:35.441 When they evaporate away, do they return the information 00:45:35.521 --> 00:45:39.401 about everything that ever fell in back to the universe? 00:46:27.360 --> 00:46:30.408 If information somehow escapes from 00:46:30.432 --> 00:46:33.480 sagittarius a as it evaporates away, 00:46:35.281 --> 00:46:37.921 the implication is profound. 00:46:40.881 --> 00:46:43.241 Black holes aren't tombs. 00:46:44.121 --> 00:46:45.321 They're gateways. 00:46:48.881 --> 00:46:55.281 We now believe that anything that falls into sagittarius a will live on, 00:46:59.521 --> 00:47:03.561 not as a physical object but as information... 00:47:09.521 --> 00:47:11.961 Escaping from the heart of darkness, 00:47:13.361 --> 00:47:17.601 encoded in the Hawking radiation in the far future. 00:47:28.401 --> 00:47:32.241 The memory of all those worlds that fell into sagittarius a, 00:47:32.321 --> 00:47:35.441 of the entire history of the milky way galaxy, 00:47:35.521 --> 00:47:39.481 is somehow written in the ashes of the universe in the far future. 00:47:43.041 --> 00:47:45.801 But the real treasure lies in the explanation 00:47:45.881 --> 00:47:50.001 of how the information gets out from those eternal prisons. 00:47:50.361 --> 00:47:53.401 Now, what I'm going to tell you is going to sound absolutely bizarre. 00:47:53.481 --> 00:47:55.521 It's going to sound like science fiction. 00:47:56.161 --> 00:47:57.601 But here goes. 00:47:57.681 --> 00:48:02.561 When the black hole is evaporated away, about half of it is gone. 00:48:03.241 --> 00:48:07.721 The interior becomes, in some sense, the same place 00:48:07.801 --> 00:48:12.041 as the distant Hawking radiation that was emitted aeons ago 00:48:12.121 --> 00:48:14.881 that's out there in the far reaches of the universe. 00:48:15.401 --> 00:48:19.401 It seems that spacetime wormholes open up 00:48:19.481 --> 00:48:24.321 between the interior of the black hole and those distant parts of the universe. 00:48:24.401 --> 00:48:29.281 And it's that that allows us to read the information inside. 00:48:29.361 --> 00:48:32.761 Now, that is supposed to sound weird, 00:48:32.841 --> 00:48:36.001 and I should say that nobody really agrees 00:48:36.081 --> 00:48:38.641 on the physical picture of what's happening. 00:48:38.721 --> 00:48:42.001 But what everybody agrees on is this. 00:48:42.081 --> 00:48:43.841 The black holes are telling us 00:48:43.921 --> 00:48:49.601 that our intuitive picture of reality, of space and time is wrong. 00:48:49.681 --> 00:48:54.001 The idea that this place is close to this place, 00:48:54.081 --> 00:48:57.121 and that time ticks along is wrong. 00:48:57.201 --> 00:49:03.841 There is a deeper picture of reality in which space and time do not exist. 00:49:13.161 --> 00:49:16.281 Our attempt to answer a seemingly simple question 00:49:17.761 --> 00:49:21.241 about the fate of objects that fall into black holes 00:49:21.321 --> 00:49:26.401 has led us to a profound, and quite unsettling conclusion. 00:49:29.041 --> 00:49:35.001 Space and time, concepts so foundational to how we experience the world 00:49:35.961 --> 00:49:39.561 are not fundamental properties of nature. 00:49:42.881 --> 00:49:49.721 They emerge from a deeper reality in which neither exist. 00:49:53.881 --> 00:50:00.601 The thing about black holes is that nobody really understands them. 00:50:00.681 --> 00:50:05.281 So, don't worry if you don't understand what I'm talking about 00:50:05.361 --> 00:50:07.561 because I don't understand what I'm talking about, 00:50:07.641 --> 00:50:09.241 and nobody else does either. 00:50:20.521 --> 00:50:22.281 We 're still a long way 00:50:22.361 --> 00:50:26.481 from fully comprehending the secrets of black holes. 00:50:30.001 --> 00:50:32.081 But we are beginning to lift the veil. 00:50:38.441 --> 00:50:41.521 Far from being a mere cosmic aberration, 00:50:44.201 --> 00:50:48.641 sagittarius a is a part of our history 00:50:48.721 --> 00:50:51.481 and of our future. 00:50:53.121 --> 00:50:56.721 Our black hole not only made us who we are today, 00:50:58.521 --> 00:51:00.201 it's our teacher, 00:51:01.521 --> 00:51:05.481 slowly revealing the deepest mysteries of the universe, 00:51:07.481 --> 00:51:10.521 secrets sealed away for so long 00:51:12.961 --> 00:51:16.081 inside a place beyond forever. 00:51:21.761 --> 00:51:24.761 The moral of the story is this. 00:51:24.841 --> 00:51:27.361 Understanding the book of nature is hard. 00:51:27.921 --> 00:51:29.561 And so, the more of nature we observe, 00:51:29.641 --> 00:51:32.441 the more chance we have of finishing the book. 00:51:32.881 --> 00:51:38.161 Now, the strangest objects in nature, by far, are black holes. 00:51:38.241 --> 00:51:39.801 And so, I suppose, it's not surprising 00:51:39.881 --> 00:51:43.041 that by peering over the horizon and into the darkness, 00:51:43.121 --> 00:51:46.081 we have caught a glimpse of something deeply hidden, 00:51:46.681 --> 00:51:50.681 the underlying structure of reality itself. 00:51:53.521 --> 00:51:55.881 So, if we want to understand the meaning of it all, 00:51:55.961 --> 00:51:58.161 we can't restrict ourselves 00:51:58.241 --> 00:52:01.201 to the intellectually safe confines of our planet. 00:52:01.801 --> 00:52:05.681 We have to look out there, to the universe beyond. 00:52:53.241 --> 00:52:57.201 Grant tremblay: So, of the seemingly endless zoo of objects in our universe, 00:52:57.321 --> 00:53:01.161 from clouds of gas, to planets, to stars, galaxies, what have you, 00:53:01.241 --> 00:53:05.401 black holes are probably one of the most fundamentally important 00:53:05.481 --> 00:53:08.721 singular class of objects that we can study, 00:53:09.441 --> 00:53:12.081 a place where the laws of physics literally break do wn. 00:53:12.601 --> 00:53:16.241 We have theories, but we can't really know what's happening. 00:53:16.881 --> 00:53:19.801 David kaiser: So, black holes present this remarkable invitation 00:53:19.881 --> 00:53:22.161 to physicists, mathematicians, astronomers. 00:53:22.241 --> 00:53:24.401 One of the best tools we have to study 00:53:24.481 --> 00:53:27.321 these exotic phenomena is the chandra telescope. 00:53:32.801 --> 00:53:34.761 Chandra's kind of like a black hole hunter, 00:53:34.841 --> 00:53:38.521 finding them near and far throughout the galaxy and the universe. 00:53:38.601 --> 00:53:42.281 Woman: Just a few minutes away from the 26th flight of the shuttle, Columbia, 00:53:42.361 --> 00:53:43.601 with a crew of five. 00:53:50.481 --> 00:53:53.601 Kimberly arcan d: I think a night launch is particularly exciting. 00:53:54.241 --> 00:53:56.401 Woman: We have a go for engine start. 00:53:57.361 --> 00:54:00.841 We have booster ignition, lift-off of co lu m bia. 00:54:05.161 --> 00:54:07.041 Arcan d: You just see fire. 00:54:07.121 --> 00:54:10.161 It lights up the night sky in the most beautiful way. 00:54:10.681 --> 00:54:13.801 Man: Colu m bia now has burned more than two million pounds of fuel 00:54:13.881 --> 00:54:15.761 and weighs half of what it did at launch. 00:54:15.841 --> 00:54:18.841 Its huge. Chandra is about the size of a school bus. 00:54:18.921 --> 00:54:23.281 It's the largest telescope to ever be launched by the space shuttle. 00:54:29.361 --> 00:54:31.161 Man: Srb separation is confirmed. 00:54:31.961 --> 00:54:35.041 You're stressed about the astronauts on board that are literally 00:54:35.121 --> 00:54:39.401 risking their lives to help us get a better view of the universe. 00:54:42.641 --> 00:54:45.161 When the main engine's cut off we 're in zero-g. 00:54:45.241 --> 00:54:48.001 We separate the tank and we 're orbiting the earth. 00:54:50.001 --> 00:54:52.901 And when we 're sure that everyone is ready at mission control, 00:54:52.921 --> 00:54:55.321 then, I go ahead and pull the switch marked ”deploy”. 00:54:55.761 --> 00:54:58.881 And you're looking at the deploy of the chandra x—ra y observatory. 00:55:00.201 --> 00:55:04.041 Chandra is an X-ray telescope, which means that it can see 00:55:04.121 --> 00:55:07.121 the most energetic light coming at us from the universe. 00:55:07.841 --> 00:55:11.401 The telescope has to be outside the earth's atmosphere 00:55:11.481 --> 00:55:15.361 because the earth's atmosphere, thankfully for us, blocks out x-rays. 00:55:15.441 --> 00:55:17.001 Otherwise, we'd just get fried. 00:55:19.561 --> 00:55:20.921 Kaiser: The chandra satellite, 00:55:21.001 --> 00:55:24.041 by rising above the atmosphere, has a much clearer view. 00:55:25.041 --> 00:55:27.881 Why is that so interesting for studying things like black holes? 00:55:27.961 --> 00:55:32.281 Black holes can excite matter in their vicinity to very high energies. 00:55:32.361 --> 00:55:35.801 They can get atoms and parts of atoms whipping around, 00:55:35.881 --> 00:55:40.001 and by re wing up those particles to very, very high energies, 00:55:40.081 --> 00:55:41.601 they will radiate. 00:55:42.281 --> 00:55:45.241 So, we can gather enormous amounts of information 00:55:45.321 --> 00:55:48.201 about the immediate vicinity of a black hole. 00:55:52.041 --> 00:55:56.361 When we look at sagittarius a today, it's quiet and not doing very much. 00:55:56.441 --> 00:55:59.081 But when we look at other supermassive black holes in the universe, 00:55:59.121 --> 00:56:00.161 they're active. 00:56:02.881 --> 00:56:04.761 Arcan d: So, you can take chandra and watch 00:56:04.841 --> 00:56:08.641 a black hole have a small snack, maybe like a human might have 00:56:08.721 --> 00:56:12.201 a little biscuit in the afternoon. And it's something like an asteroid, 00:56:12.281 --> 00:56:15.961 and there will be a small sort of X-ray signature from that event. 00:56:16.441 --> 00:56:21.121 But you can also see a black hole have a really, really big snack 00:56:21.201 --> 00:56:23.321 and chandra's able to witness that as well. 00:56:24.801 --> 00:56:26.201 Tremblay: Chandra has witnessed 00:56:26.281 --> 00:56:29.441 the destruction of a star by a black hole itself right? 00:56:29.521 --> 00:56:33.201 So, this poor star wanders in to the black hole, 00:56:34.681 --> 00:56:38.001 then, it rips the star apart, it shears it, right? 00:56:38.081 --> 00:56:40.921 And then, the corpse of that star, 00:56:41.001 --> 00:56:42.881 this sort of spaghetti-fied matter 00:56:42.961 --> 00:56:45.601 that starts spiralling around the event horizon, 00:56:45.681 --> 00:56:47.001 lights up in x-rays. 00:56:49.161 --> 00:56:53.801 So, to be witness to that, to observe the destruction of a star, 00:56:53.881 --> 00:56:59.241 you know, in time, it was just extraordinary. It's just unbelievable. 00:57:02.001 --> 00:57:05.161 Arcan d: There's this one pretty famous image that chandra took 00:57:05.241 --> 00:57:07.956 called the chandra deep field-south, 00:57:07.980 --> 00:57:10.321 and it's the deepest x—ra y image ever. 00:57:10.401 --> 00:57:14.161 In that one dataset, there's thousands of black holes, 00:57:14.241 --> 00:57:17.001 like, maybe 5, 000 of them, if not more. 00:57:17.081 --> 00:57:21.961 And it just kind of helps show you that they're all over the place 00:57:22.041 --> 00:57:24.241 and there's so much more to discover.