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These are the user uploaded subtitles that are being translated: 1 00:00:01,139 --> 00:00:03,244 Viewers like you make this program possible. 2 00:00:03,279 --> 00:00:05,350 Support your local PBS station. 3 00:00:13,116 --> 00:00:16,913 Something is hiding in the darkness. 4 00:00:16,947 --> 00:00:20,192 Invisible objects of unimaginable power 5 00:00:20,227 --> 00:00:26,336 that could hold the key to solving the mysteries of space, 6 00:00:26,371 --> 00:00:30,720 time, and the universe itself. 7 00:00:30,754 --> 00:00:33,136 To me, a black hole is 8 00:00:33,171 --> 00:00:37,623 the greatest exhibition of nature's mysterious powers. 9 00:00:37,658 --> 00:00:39,556 You literally can't see them. 10 00:00:39,591 --> 00:00:41,558 And that's what makes them extremely mysterious. 11 00:00:41,593 --> 00:00:45,631 They are bizarre quirks of nature. 12 00:00:45,666 --> 00:00:46,839 When we're studying black holes, 13 00:00:46,874 --> 00:00:48,565 we're right on the edge of human knowledge. 14 00:00:51,051 --> 00:00:53,984 And yet, they are sculptors of the cosmos. 15 00:00:54,019 --> 00:00:58,265 The jets from black holes are so powerful, they can affect 16 00:00:58,299 --> 00:01:00,715 the whole shape and nature of a galaxy. 17 00:01:00,750 --> 00:01:05,065 Even shaping our own galaxy, the Milky Way. 18 00:01:05,099 --> 00:01:06,411 We had hints that black holes 19 00:01:06,445 --> 00:01:08,896 were at the center of all of galaxies, like our own. 20 00:01:08,930 --> 00:01:12,313 Can we lift the veil... 21 00:01:12,348 --> 00:01:13,418 Forget the one-way trip to Mars. 22 00:01:13,452 --> 00:01:14,833 I'm going in the black hole. 23 00:01:17,560 --> 00:01:19,976 And reveal their secrets? 24 00:01:20,010 --> 00:01:21,909 Fermi revealed something completely astonishing 25 00:01:21,943 --> 00:01:23,531 and unexpected. 26 00:01:23,566 --> 00:01:26,707 We've never seen anything like it. 27 00:01:26,741 --> 00:01:30,711 Finding these little pieces of the puzzle that did not fit 28 00:01:30,745 --> 00:01:33,196 is super-exciting. 29 00:01:33,231 --> 00:01:35,060 But if you really want to understand 30 00:01:35,095 --> 00:01:36,924 the deepest questions of the universe, 31 00:01:36,958 --> 00:01:38,684 you have to understand black holes. 32 00:01:43,206 --> 00:01:45,381 "Black Holes," 33 00:01:45,415 --> 00:01:48,142 right now, on "NOVA." 34 00:02:28,286 --> 00:02:30,874 As we gaze out at the Milky Way, 35 00:02:30,909 --> 00:02:33,463 our eyes are drawn to the light. 36 00:02:35,534 --> 00:02:38,227 Hundreds of billions of stars 37 00:02:38,261 --> 00:02:43,439 serenely spinning through the cosmos. 38 00:02:43,473 --> 00:02:45,337 When we look up at the night sky, 39 00:02:45,372 --> 00:02:48,789 the stars and planets that we see are beautiful. 40 00:02:48,823 --> 00:02:51,516 But actually, it's in the space between these, 41 00:02:51,550 --> 00:02:52,689 in the dark patches, 42 00:02:52,724 --> 00:02:56,141 that some of the most fascinating things lie. 43 00:02:59,558 --> 00:03:02,216 In places where there is no light, 44 00:03:02,251 --> 00:03:08,326 objects of profound mystery bide their time. 45 00:03:08,360 --> 00:03:12,537 Awesome in their simplicity and perfection, 46 00:03:12,571 --> 00:03:15,885 we call them black holes. 47 00:03:15,919 --> 00:03:17,266 A black hole 48 00:03:17,300 --> 00:03:22,443 is an infinitely dense point in space from which nothing 49 00:03:22,478 --> 00:03:24,618 can escape, not even light. 50 00:03:24,652 --> 00:03:27,724 It's extraordinary to think that black holes are everywhere 51 00:03:27,759 --> 00:03:29,139 in the universe, 52 00:03:29,174 --> 00:03:35,249 that they have existed from very early times in the universe. 53 00:03:35,284 --> 00:03:39,288 When quiet, they are almost impossible to detect. 54 00:03:39,322 --> 00:03:40,979 We're talking about a region of space 55 00:03:41,013 --> 00:03:42,394 where, if something falls in, 56 00:03:42,429 --> 00:03:43,947 we'll never know about it ever again. 57 00:03:46,260 --> 00:03:50,333 They hold the power to shred stars and worlds, 58 00:03:50,368 --> 00:03:56,684 but also, the potential to shape galaxies... 59 00:03:56,719 --> 00:03:59,515 Black holes are one of the most fundamentally important 60 00:03:59,549 --> 00:04:03,933 singular objects that might dictate how galaxies 61 00:04:03,967 --> 00:04:05,935 form and evolve. 62 00:04:05,969 --> 00:04:07,557 It's natural to fear them, 63 00:04:07,592 --> 00:04:09,214 but we're learning that they're essential. 64 00:04:09,249 --> 00:04:10,595 You can't live with them, 65 00:04:10,629 --> 00:04:12,597 but you also can't live without them. 66 00:04:16,117 --> 00:04:18,775 And they may hold the secret to the ultimate fate 67 00:04:18,810 --> 00:04:21,468 of the universe. 68 00:04:21,502 --> 00:04:23,124 Black holes, on a fundamental level, 69 00:04:23,159 --> 00:04:26,576 challenge our understanding of physics, 70 00:04:26,611 --> 00:04:30,925 of the way that everything in the universe works. 71 00:04:30,960 --> 00:04:33,273 Black holes are the most mysterious objects 72 00:04:33,307 --> 00:04:34,895 in the universe, full stop. 73 00:04:39,900 --> 00:04:46,009 To understand black holes, we have to start at the beginning. 74 00:04:46,044 --> 00:04:50,531 At the moment of birth. 75 00:04:50,566 --> 00:04:54,777 Black holes that are a few times the mass of the sun 76 00:04:54,811 --> 00:04:58,539 probably formed from giant stars that were maybe about 77 00:04:58,574 --> 00:05:01,611 20 to 30 times the mass of the sun. 78 00:05:04,890 --> 00:05:11,690 Enormous stars burning bright blue with intense heat. 79 00:05:11,725 --> 00:05:16,177 But the brightest stars are the shortest-lived. 80 00:05:16,212 --> 00:05:19,180 A star is a big ball of gas, right? 81 00:05:19,215 --> 00:05:20,872 There's outward gravity pushing in, right? 82 00:05:20,906 --> 00:05:22,494 The thing wants to collapse in on itself 83 00:05:22,529 --> 00:05:24,047 under its own self-gravity. 84 00:05:24,082 --> 00:05:26,187 But the fusion that's happening within the star's core 85 00:05:26,222 --> 00:05:30,330 liberates so much light that the outward radiation pressure 86 00:05:30,364 --> 00:05:32,193 prevents the collapse of that star. 87 00:05:34,506 --> 00:05:37,544 But eventually, that gives up. 88 00:05:37,578 --> 00:05:43,377 A star like that can burn through its nuclear fuel 89 00:05:43,412 --> 00:05:46,346 in just a few million years. 90 00:05:57,011 --> 00:05:59,704 And when its power source runs out, 91 00:05:59,738 --> 00:06:05,537 it collapses under its own gravitational pull. 92 00:06:05,572 --> 00:06:08,402 There's so much material that's collapsing during 93 00:06:08,437 --> 00:06:13,373 their final few moments that they create this massive 94 00:06:13,407 --> 00:06:15,478 dense ball of neutrons 95 00:06:15,513 --> 00:06:20,449 that continues to collapse. 96 00:06:20,483 --> 00:06:25,281 A star 20 times the mass of our sun or larger... 97 00:06:27,007 --> 00:06:31,943 crushed by the force of gravity, 98 00:06:31,977 --> 00:06:37,638 until the star disappears, 99 00:06:37,673 --> 00:06:40,952 leaving only a ghost behind. 100 00:06:44,024 --> 00:06:46,751 A black hole. 101 00:06:49,547 --> 00:06:53,723 This transformation does not await all stars. 102 00:06:53,758 --> 00:06:58,210 Smaller, less massive stars, like our sun, 103 00:06:58,245 --> 00:07:02,042 eventually become burnt-out dwarves when their fusion stops: 104 00:07:02,076 --> 00:07:07,427 slowly fading cinders. 105 00:07:07,461 --> 00:07:10,119 But it's possible that almost all the massive stars 106 00:07:10,153 --> 00:07:14,330 that dominated the early universe formed black holes 107 00:07:14,364 --> 00:07:18,368 when they died. 108 00:07:18,403 --> 00:07:21,993 Because black holes are simply what happens when enough matter 109 00:07:22,027 --> 00:07:25,893 is crushed into a small enough volume, 110 00:07:25,928 --> 00:07:29,587 dramatically warping the space around it. 111 00:07:29,621 --> 00:07:32,417 A river is a great analogy for the area right around 112 00:07:32,452 --> 00:07:33,901 a black hole. 113 00:07:33,936 --> 00:07:38,768 Here I am far upstream, and the water is fairly placid. 114 00:07:38,803 --> 00:07:40,494 It's not moving too fast. 115 00:07:40,529 --> 00:07:43,083 If I were to get into the water here and swim across, 116 00:07:43,117 --> 00:07:46,396 I'd be able to do that very easily. 117 00:07:46,431 --> 00:07:48,640 In the same way, if you're far away from a black hole, 118 00:07:48,675 --> 00:07:51,609 you'll be able to get around with just a normal spacecraft 119 00:07:51,643 --> 00:07:55,336 without too much trouble and simple propulsion. 120 00:07:59,996 --> 00:08:02,585 But the closer you get to the black hole, 121 00:08:02,620 --> 00:08:06,624 the stranger things become. 122 00:08:06,658 --> 00:08:09,454 The collapsed massive star crushes down 123 00:08:09,489 --> 00:08:11,732 so small and so dense, 124 00:08:11,767 --> 00:08:15,287 it ceases to have a physical surface at all, 125 00:08:15,322 --> 00:08:20,051 becoming an infinitely small point in space, 126 00:08:20,085 --> 00:08:26,609 exerting a profound effect on the space-time around it. 127 00:08:26,644 --> 00:08:30,544 As the water gets closer to the waterfall, 128 00:08:30,579 --> 00:08:33,409 the speed of the water increases. 129 00:08:33,443 --> 00:08:37,413 If I were to jump into the water right here, 130 00:08:37,447 --> 00:08:39,588 the speed of the current would be so intense 131 00:08:39,622 --> 00:08:42,280 that I wouldn't be able to swim against it, 132 00:08:42,314 --> 00:08:45,214 and I would be gradually pulled closer to the edge 133 00:08:45,248 --> 00:08:47,837 of the waterfall till I reach a point of no return. 134 00:08:47,872 --> 00:08:50,564 And that's the same around a black hole. 135 00:08:53,222 --> 00:08:57,882 Just outside the black hole, the fabric of space itself 136 00:08:57,916 --> 00:09:01,851 actually stretches inward towards the center. 137 00:09:03,957 --> 00:09:08,755 Not even stars, planets, people, even light cannot escape 138 00:09:08,789 --> 00:09:10,515 the pull of a black hole. 139 00:09:10,550 --> 00:09:13,622 It's like a waterfall in the fabric of the universe. 140 00:09:16,763 --> 00:09:22,251 The black hole's gravitational reach is not infinite. 141 00:09:22,285 --> 00:09:24,909 People have this idea that black holes suck, 142 00:09:24,943 --> 00:09:27,118 in the sense that they suck everything into them, 143 00:09:27,152 --> 00:09:28,429 but that's not true. 144 00:09:28,464 --> 00:09:31,640 Black holes can only eat things that are within 145 00:09:31,674 --> 00:09:34,815 a certain distance away from them. 146 00:09:34,850 --> 00:09:36,368 If you're further away, 147 00:09:36,403 --> 00:09:42,512 then the black hole has no way of eating you. 148 00:09:42,547 --> 00:09:46,827 But once in its grasp, you are lost forever. 149 00:09:46,862 --> 00:09:50,866 And this is the key to their mystery. 150 00:09:50,900 --> 00:09:54,697 The black hole's interior is hidden from view, 151 00:09:54,732 --> 00:09:59,737 cut off from the rest of the universe by a boundary in space: 152 00:09:59,771 --> 00:10:03,326 the event horizon. 153 00:10:03,361 --> 00:10:06,744 Beyond this point, there is no escape. 154 00:10:12,612 --> 00:10:15,062 As we approach the event horizon, 155 00:10:15,097 --> 00:10:20,999 we get our first glimpse of the true weirdness of black holes. 156 00:10:24,313 --> 00:10:26,108 Ever since Einstein, 157 00:10:26,142 --> 00:10:27,937 we've viewed the fabric of the universe 158 00:10:27,972 --> 00:10:32,493 not as something static, but instead something that's fluid, 159 00:10:32,528 --> 00:10:37,084 something that bends and warps around objects with mass. 160 00:10:37,119 --> 00:10:41,537 We call this space-time, a combination of space and time. 161 00:10:41,571 --> 00:10:45,921 See, Einstein's insight was to realize that these two things 162 00:10:45,955 --> 00:10:47,992 are intimately connected. 163 00:10:48,026 --> 00:10:52,652 That when an object has mass, it not just bends space, 164 00:10:52,686 --> 00:10:55,862 but changes the passage of time itself. 165 00:10:55,896 --> 00:11:01,039 In particular, the effect of a mass is to slow time down. 166 00:11:02,938 --> 00:11:05,250 In the region around the black hole, 167 00:11:05,285 --> 00:11:06,389 the warped space-time 168 00:11:06,424 --> 00:11:11,981 elongates light waves, distorting color. 169 00:11:12,016 --> 00:11:15,536 The event horizon is the place at which time stops 170 00:11:15,571 --> 00:11:17,297 when seen from far away. 171 00:11:17,331 --> 00:11:19,851 Someone who's outside the black hole will see you get 172 00:11:19,886 --> 00:11:21,646 redder and redder... 173 00:11:21,681 --> 00:11:24,062 And your time will slow down. 174 00:11:24,097 --> 00:11:25,857 And you'll kind of pass through 175 00:11:25,892 --> 00:11:27,341 the horizon, disappear forever. 176 00:12:04,551 --> 00:12:11,558 Black holes are like waterfalls in the fabric of the universe, 177 00:12:11,592 --> 00:12:16,943 where space contorts and time itself grinds to a halt, 178 00:12:16,977 --> 00:12:19,877 ensnaring light, 179 00:12:19,911 --> 00:12:25,917 making them lockboxes for the universe's ultimate secrets. 180 00:12:39,482 --> 00:12:43,693 It is said that fact is sometimes stranger than fiction, 181 00:12:43,728 --> 00:12:48,146 and nowhere is that more true than in the case of black holes. 182 00:12:50,217 --> 00:12:53,703 Black holes are stranger than anything dreamed up 183 00:12:53,738 --> 00:12:55,671 by science fiction writers, 184 00:12:55,705 --> 00:12:59,088 but they are firmly matters of science fact. 185 00:13:05,923 --> 00:13:09,374 The vast majority of black holes are small... 186 00:13:09,409 --> 00:13:12,792 less than 20 miles across... 187 00:13:12,826 --> 00:13:17,831 and they usually wander alone through space. 188 00:13:17,866 --> 00:13:21,214 But if we turn our gaze towards the center of the Milky Way 189 00:13:21,248 --> 00:13:23,181 and journey inwards, 190 00:13:23,216 --> 00:13:29,084 through the gas and dust that shroud the galactic core, 191 00:13:29,118 --> 00:13:32,846 signs of something altogether different appear. 192 00:13:32,881 --> 00:13:34,330 If you simply observe 193 00:13:34,365 --> 00:13:38,334 the stars in the very heart of our galaxy over about 20 years, 194 00:13:38,369 --> 00:13:41,234 you will observe them orbiting nothing. 195 00:13:43,995 --> 00:13:48,068 At the center of this swarm of stars is darkness. 196 00:13:48,103 --> 00:13:50,070 It's a void. 197 00:13:50,105 --> 00:13:55,524 Scientists name this invisible enigma Sagittarius A-star, 198 00:13:55,558 --> 00:13:58,838 although it is not a star at all. 199 00:13:58,872 --> 00:14:00,080 Can you imagine 200 00:14:00,115 --> 00:14:03,808 how massive that object has to be to be able to pull 201 00:14:03,843 --> 00:14:06,017 entire stars into orbit? 202 00:14:07,985 --> 00:14:10,056 They believe it to be a black hole 203 00:14:10,090 --> 00:14:14,267 more than four million times the mass of our sun... 204 00:14:14,301 --> 00:14:15,924 many thousands of times more massive 205 00:14:15,958 --> 00:14:19,030 than any other in the Milky Way. 206 00:14:19,065 --> 00:14:20,238 How did this monster 207 00:14:20,273 --> 00:14:22,723 come to live at the heart of the Milky Way? 208 00:14:22,758 --> 00:14:28,419 Sagittarius A-star is a supermassive giant 209 00:14:28,453 --> 00:14:32,699 around which the entire galaxy spins, 210 00:14:32,733 --> 00:14:36,910 raising intriguing new questions about the role of black holes 211 00:14:36,945 --> 00:14:40,569 in our galaxy and the universe. 212 00:14:40,603 --> 00:14:42,536 How did it get there? 213 00:14:42,571 --> 00:14:45,436 How did it get so big? 214 00:14:45,470 --> 00:14:48,508 And what can it tell us about how black holes 215 00:14:48,542 --> 00:14:50,924 shape the cosmos? 216 00:14:50,959 --> 00:14:52,615 Would we even be here today 217 00:14:52,650 --> 00:14:54,376 without Sagittarius A-star? 218 00:14:59,864 --> 00:15:01,866 Just a few minutes away from the 26th flight 219 00:15:01,901 --> 00:15:03,178 of the shuttle Columbia, 220 00:15:03,212 --> 00:15:04,938 with a crew of five. 221 00:15:11,669 --> 00:15:14,948 I think a night launch is particularly exciting. 222 00:15:14,983 --> 00:15:17,847 Go for engine start. 223 00:15:17,882 --> 00:15:21,541 We have booster ignition and lift-off of Columbia. 224 00:15:21,575 --> 00:15:23,923 Roger roll, Columbia, we're looking in. 225 00:15:25,545 --> 00:15:27,961 Chandra is huge. 226 00:15:27,996 --> 00:15:29,376 It's about the size of a school bus. 227 00:15:29,411 --> 00:15:30,860 It's the largest telescope 228 00:15:30,895 --> 00:15:33,622 to ever be launched by the space shuttle. 229 00:15:37,350 --> 00:15:41,112 SRB separation is confirmed. 230 00:15:41,147 --> 00:15:42,907 You're stressed about the astronauts onboard 231 00:15:42,942 --> 00:15:45,461 that are literally risking their lives to help us 232 00:15:45,496 --> 00:15:48,119 get a better view of the universe. 233 00:15:52,537 --> 00:15:55,747 In the summer of 1999, 234 00:15:55,782 --> 00:15:59,234 NASA's flagship telescope for X-ray astronomy 235 00:15:59,268 --> 00:16:03,410 sets off from the space shuttle cargo bay. 236 00:16:08,070 --> 00:16:10,762 Even two decades into its voyage of discovery, 237 00:16:10,797 --> 00:16:14,594 Chandra remains by far the most powerful observatory 238 00:16:14,628 --> 00:16:17,217 that we have to observe the high-energy universe. 239 00:16:21,946 --> 00:16:26,675 Almost 83,000 miles above the Earth's surface, 240 00:16:26,709 --> 00:16:32,163 at its highest orbit, Chandra scans the sky 241 00:16:32,198 --> 00:16:35,339 with eight high-precision mirrors engineered 242 00:16:35,373 --> 00:16:40,102 to detect X-rays emitted from extremely hot regions 243 00:16:40,137 --> 00:16:41,586 of the universe. 244 00:16:43,588 --> 00:16:49,146 For 14 years, it searches among the exploding stars 245 00:16:49,180 --> 00:16:52,287 and clusters of galaxies. 246 00:16:54,841 --> 00:16:59,156 But then, on September 14, 2013, 247 00:16:59,190 --> 00:17:04,609 Chandra chances on something else entirely. 248 00:17:04,644 --> 00:17:06,715 Chandra wasn't looking for this at all... 249 00:17:06,749 --> 00:17:08,717 just happened to be looking nearby. 250 00:17:08,751 --> 00:17:10,408 So it was a total surprise. 251 00:17:15,551 --> 00:17:20,418 As the telescope gazes into the constellation of Sagittarius, 252 00:17:20,453 --> 00:17:24,491 it aims to observe a large cloud of hot gas. 253 00:17:24,526 --> 00:17:28,633 But unexpectedly, 254 00:17:28,668 --> 00:17:33,707 it records a flash of X-rays just a few pixels across 255 00:17:33,742 --> 00:17:40,231 coming from the seemingly empty space in the galactic core. 256 00:17:48,688 --> 00:17:50,931 When we see something get very hot for a very short period 257 00:17:50,966 --> 00:17:53,417 of time, we get very excited. 258 00:17:53,451 --> 00:17:56,282 Something is causing it... something we can't see. 259 00:18:04,600 --> 00:18:08,777 Some scientists believe the flash seen by Chandra 260 00:18:08,811 --> 00:18:11,745 is caused by an asteroid... 261 00:18:17,786 --> 00:18:21,307 ripped apart and burning up in a blaze 262 00:18:21,341 --> 00:18:25,897 hundreds of times brighter than the sun, 263 00:18:25,932 --> 00:18:30,419 releasing a burst of X-rays that Chandra can detect 264 00:18:30,454 --> 00:18:35,010 almost 26,000 light-years away. 265 00:18:35,044 --> 00:18:37,771 If we see a level of X-rays being produced that's so bright, 266 00:18:37,806 --> 00:18:39,118 it can't be explained 267 00:18:39,152 --> 00:18:41,913 by any other process, then we know that there must be 268 00:18:41,948 --> 00:18:43,812 a black hole there. 269 00:18:43,846 --> 00:18:47,574 It's the behemoth at the center of our galaxy. 270 00:18:51,026 --> 00:18:53,960 Sagittarius A-star. 271 00:19:02,417 --> 00:19:05,834 You can take a telescope like Chandra and watch a black hole 272 00:19:05,868 --> 00:19:07,387 have a small snack, 273 00:19:07,422 --> 00:19:10,114 maybe like a human might have a little biscuit in the afternoon. 274 00:19:10,149 --> 00:19:12,427 And it's something like an asteroid. 275 00:19:12,461 --> 00:19:14,601 And there will be a small sort of X-ray signature 276 00:19:14,636 --> 00:19:15,637 from that event. 277 00:19:15,671 --> 00:19:16,914 So it's incredible 278 00:19:16,948 --> 00:19:19,813 that we can actually observe Sagittarius A-star, 279 00:19:19,848 --> 00:19:22,506 which lies 26,000 light-years away, 280 00:19:22,540 --> 00:19:26,889 actually eating something. 281 00:19:26,924 --> 00:19:29,098 But Chandra does not only look inwards. 282 00:19:29,133 --> 00:19:34,690 It also looks out, beyond the Milky Way. 283 00:19:34,725 --> 00:19:39,661 At the center of almost every large galaxy Chandra peers into, 284 00:19:39,695 --> 00:19:44,666 it finds evidence that our galaxy is hardly unusual. 285 00:19:44,700 --> 00:19:46,978 We started to spot 286 00:19:47,013 --> 00:19:49,912 X-ray sources of light everywhere around the sky, 287 00:19:49,947 --> 00:19:52,743 and we started to realize something weird was going on 288 00:19:52,777 --> 00:19:54,400 in the centers of galaxies. 289 00:19:57,299 --> 00:19:59,715 At the heart of most galaxies, 290 00:19:59,750 --> 00:20:02,062 we think now there are supermassive black holes, 291 00:20:02,097 --> 00:20:04,410 black holes that weigh millions or billions of times 292 00:20:04,444 --> 00:20:06,135 what our sun does. 293 00:20:06,170 --> 00:20:10,485 It's incredible that our modern X-ray telescopes, like Chandra, 294 00:20:10,519 --> 00:20:12,625 allow us to map out 295 00:20:12,659 --> 00:20:16,801 where these fascinating black holes are across the universe. 296 00:20:18,527 --> 00:20:22,497 Supermassive black holes seem to be an integral feature 297 00:20:22,531 --> 00:20:24,878 of the cosmos. 298 00:20:24,913 --> 00:20:29,849 But these supermassive objects raise questions. 299 00:20:29,883 --> 00:20:32,196 How do they form? 300 00:20:32,231 --> 00:20:36,027 And why are they so big? 301 00:20:36,062 --> 00:20:39,548 These things form over millions to billions of years. 302 00:20:39,583 --> 00:20:41,654 So we can't watch this happening. 303 00:20:41,688 --> 00:20:44,277 We can only see it at various different stages 304 00:20:44,312 --> 00:20:45,934 throughout the universe. 305 00:20:45,968 --> 00:20:50,352 And so we have to just piece it together like a jigsaw puzzle. 306 00:20:50,387 --> 00:20:54,287 Some scientists theorize that the biggest and oldest 307 00:20:54,322 --> 00:20:59,223 black holes did not start life as stars at all. 308 00:20:59,258 --> 00:21:01,777 In the very early universe, we believe that 309 00:21:01,812 --> 00:21:04,746 you could have formed very massive black hole seeds 310 00:21:04,780 --> 00:21:07,680 by direct collapse of gas. 311 00:21:07,714 --> 00:21:11,649 So these black holes are called direct-collapse black holes. 312 00:21:11,684 --> 00:21:15,584 But the jury is still out. 313 00:21:15,619 --> 00:21:18,277 It's possible that Sagittarius A-star formed 314 00:21:18,311 --> 00:21:20,865 by direct collapse of material. 315 00:21:20,900 --> 00:21:24,628 What I think is more likely is that it formed by 316 00:21:24,662 --> 00:21:26,354 the death of a star. 317 00:21:26,388 --> 00:21:32,325 However Sagittarius A-star was born, one thing is certain: 318 00:21:32,360 --> 00:21:33,982 it had to grow. 319 00:21:40,540 --> 00:21:45,752 The newly formed Sagittarius A-star begins to feast, 320 00:21:45,787 --> 00:21:50,964 gorging itself on not just asteroids, 321 00:21:50,999 --> 00:21:57,799 but bigger game, like stars and massive clouds of gas. 322 00:21:57,833 --> 00:21:59,214 As it snacks on these 323 00:21:59,248 --> 00:22:03,114 nearby objects that wander into its path, it gets bigger 324 00:22:03,149 --> 00:22:05,634 and bigger and bigger. 325 00:22:07,809 --> 00:22:11,468 The black hole gains more mass 326 00:22:11,502 --> 00:22:15,955 and more gravitational power. 327 00:22:15,989 --> 00:22:18,716 But black holes that are a few times the mass of the sun 328 00:22:18,751 --> 00:22:21,270 can never grow to be a supermassive black hole 329 00:22:21,305 --> 00:22:24,170 just by eating gas and stars. 330 00:22:27,173 --> 00:22:33,041 How did Sagittarius A-star speed up its growth? 331 00:22:33,075 --> 00:22:37,425 On September 14, 2015, an international team 332 00:22:37,459 --> 00:22:41,532 of astronomers finds a clue, 333 00:22:41,567 --> 00:22:46,399 the aftershock of a truly titanic interaction: 334 00:22:46,434 --> 00:22:50,541 two colliding black holes. 335 00:22:50,576 --> 00:22:53,337 So the merger of two black holes, as you might imagine, 336 00:22:53,372 --> 00:22:56,961 is spectacularly energetic. 337 00:22:56,996 --> 00:23:00,068 It is so energetic that it causes ripples in the fabric 338 00:23:00,102 --> 00:23:01,483 of space-time itself that propagate outward 339 00:23:01,518 --> 00:23:02,760 at the speed of light. 340 00:23:02,795 --> 00:23:06,557 And we have detected these ripples here on Earth 341 00:23:06,592 --> 00:23:10,319 with something we call LIGO. 342 00:23:10,354 --> 00:23:14,496 LIGO is an instrument that works by sending laser beams 343 00:23:14,531 --> 00:23:17,672 that bounce off of mirrors. 344 00:23:17,706 --> 00:23:22,780 When a gravitational wave passes by the Earth, 345 00:23:22,815 --> 00:23:26,370 this changes the timing of the interaction 346 00:23:26,405 --> 00:23:28,545 of those laser beams. 347 00:23:28,579 --> 00:23:31,479 The stretching caused by a merger here on Earth 348 00:23:31,513 --> 00:23:33,170 is absolutely minuscule. 349 00:23:33,204 --> 00:23:35,034 But with advanced technology, 350 00:23:35,068 --> 00:23:36,725 LIGO was able to do it. 351 00:23:46,494 --> 00:23:51,671 Many scientists now think that mergers like this are the key 352 00:23:51,706 --> 00:23:54,294 to how supermassive black holes, 353 00:23:54,329 --> 00:23:59,576 like our own, grow so big. 354 00:24:10,483 --> 00:24:15,384 When another black hole wanders towards Sagittarius A-star, 355 00:24:15,419 --> 00:24:21,736 they become locked in a gravitational embrace. 356 00:24:21,770 --> 00:24:24,911 First, it is sort of an intriguing dance. 357 00:24:24,946 --> 00:24:27,155 They kind of dance around each other, 358 00:24:27,189 --> 00:24:32,194 lose energy, and slowly spiral into each other. 359 00:24:35,991 --> 00:24:38,338 This dance gets faster and faster and faster and faster 360 00:24:38,373 --> 00:24:40,651 until they finally merge. 361 00:24:46,105 --> 00:24:50,109 Sagittarius A-star cannibalizes its cousin... 362 00:24:54,631 --> 00:24:59,946 creating ripples in the fabric of the universe itself. 363 00:24:59,981 --> 00:25:03,363 These mergers were fundamental to making Sagittarius A-star 364 00:25:03,398 --> 00:25:05,504 the monster that we see today. 365 00:25:05,538 --> 00:25:08,230 They happened billions of years ago, right at the beginning 366 00:25:08,265 --> 00:25:09,784 of Sagittarius A-star's life. 367 00:25:13,546 --> 00:25:15,306 More meals follow. 368 00:25:17,861 --> 00:25:21,381 Stars, gas clouds... 369 00:25:21,416 --> 00:25:24,315 whatever strays too close. 370 00:25:27,284 --> 00:25:31,426 And as our black hole's mass and influence grows, 371 00:25:31,460 --> 00:25:35,188 its surroundings are changing, too. 372 00:25:42,161 --> 00:25:45,716 The sea of stars and gas around the black hole 373 00:25:45,751 --> 00:25:48,650 continues to grow... 374 00:25:50,618 --> 00:25:55,208 gradually evolving into the familiar spiral disk 375 00:25:55,243 --> 00:25:58,764 we call home: 376 00:25:58,798 --> 00:26:02,664 the majestic Milky Way with the supermassive 377 00:26:02,699 --> 00:26:06,392 Sagittarius A-star at its core. 378 00:26:15,919 --> 00:26:17,403 So when Sagittarius A-star 379 00:26:17,437 --> 00:26:19,508 becomes a supermassive black hole, 380 00:26:19,543 --> 00:26:22,270 it really comes of age, and it acquires the ability 381 00:26:22,304 --> 00:26:24,617 to have a transformational impact 382 00:26:24,652 --> 00:26:27,655 on the evolution of the entire galaxy. 383 00:26:27,689 --> 00:26:30,692 Black holes are the ultimate engines in the universe. 384 00:26:30,727 --> 00:26:32,798 When you think about a car, 385 00:26:32,832 --> 00:26:34,627 the first thing you're interested in is, 386 00:26:34,662 --> 00:26:36,042 how does it work? 387 00:26:36,077 --> 00:26:39,770 You open the hood and you look at the engine of the car. 388 00:26:39,805 --> 00:26:42,290 With a black hole, you're asking, 389 00:26:42,324 --> 00:26:45,362 "I want to lift the hood up on an entire galaxy. 390 00:26:45,396 --> 00:26:48,986 How does a galaxy power itself at its very heart?" 391 00:26:56,822 --> 00:26:59,065 The center of the young galaxy 392 00:26:59,100 --> 00:27:02,931 is rich with swirling gas and dust: 393 00:27:02,966 --> 00:27:07,004 more offerings to feast on. 394 00:27:16,704 --> 00:27:20,086 This is a gluttonous period, 395 00:27:20,121 --> 00:27:24,608 a new era for Sagittarius A-star... 396 00:27:26,714 --> 00:27:32,685 when the invisible giant has the power to sculpt the galaxy. 397 00:27:38,173 --> 00:27:41,176 As Sagittarius A-star is gorging on food, 398 00:27:41,211 --> 00:27:43,351 the food that it's waiting to eat 399 00:27:43,385 --> 00:27:46,457 is swirling around the central supermassive black hole 400 00:27:46,492 --> 00:27:49,840 in this violent, energetic disk, 401 00:27:49,875 --> 00:27:55,570 and the matter is ripped apart by the gravity, 402 00:27:55,604 --> 00:27:57,848 which causes the protons and electrons to then make 403 00:27:57,883 --> 00:28:00,575 these twisted magnetic field lines. 404 00:28:00,609 --> 00:28:02,197 Everything is rotating and orbiting, 405 00:28:02,232 --> 00:28:04,821 so at the center of this black hole, 406 00:28:04,855 --> 00:28:06,029 this accretion disk, 407 00:28:06,063 --> 00:28:08,997 you have a twisted magnetic field, 408 00:28:09,032 --> 00:28:10,930 almost like a tornado. 409 00:28:10,965 --> 00:28:12,483 Right before material 410 00:28:12,518 --> 00:28:15,245 approaches that event horizon... that, 411 00:28:15,279 --> 00:28:17,696 that eternal prison, if you will... 412 00:28:17,730 --> 00:28:21,665 it can be redirected instead. 413 00:28:21,700 --> 00:28:23,702 And from the blazing tumult, 414 00:28:23,736 --> 00:28:25,980 the super-heated material 415 00:28:26,014 --> 00:28:28,810 is thrown out along the magnetic poles... 416 00:28:30,674 --> 00:28:36,991 two high-powered jets launched out into the cosmos. 417 00:28:37,025 --> 00:28:39,200 They can reach hundreds of thousands of light-years 418 00:28:39,234 --> 00:28:40,270 from the black hole itself. 419 00:28:43,963 --> 00:28:47,277 It's only recently that we've begun to grasp 420 00:28:47,311 --> 00:28:51,937 the huge influence of Sagittarius A-star on our galaxy 421 00:28:51,971 --> 00:28:55,216 and the role that those super-powered jets 422 00:28:55,250 --> 00:28:56,769 may have played. 423 00:28:56,804 --> 00:28:58,357 Engines start. 424 00:28:58,391 --> 00:29:01,498 One, zero, lift-off. 425 00:29:04,950 --> 00:29:09,299 The Delta rocket carrying a gamma ray telescope 426 00:29:09,333 --> 00:29:13,648 searching for unseen physics in the stars of the galaxies. 427 00:29:22,484 --> 00:29:25,556 Just over a decade ago, 428 00:29:25,591 --> 00:29:31,286 astronomers made a completely unexpected discovery. 429 00:29:31,321 --> 00:29:32,805 It was this whole piece of our galaxy 430 00:29:32,840 --> 00:29:35,566 that we never knew was there before. 431 00:29:35,601 --> 00:29:37,810 It would be like finding a brand-new continent on Earth. 432 00:29:42,677 --> 00:29:47,233 The Fermi space telescope was built to detect gamma rays, 433 00:29:47,268 --> 00:29:51,582 the most energetic radiation in the universe. 434 00:29:51,617 --> 00:29:53,964 Fermi is roughly 100 times as sensitive 435 00:29:53,999 --> 00:29:56,139 as previous gamma ray telescopes. 436 00:29:56,173 --> 00:29:57,796 So it has the sensitivity 437 00:29:57,830 --> 00:30:02,662 to see things that we just simply couldn't see before. 438 00:30:02,697 --> 00:30:06,839 Orbiting the Earth once every 96 minutes, 439 00:30:06,874 --> 00:30:10,705 Fermi constructs a map of the cosmos 440 00:30:10,739 --> 00:30:14,571 and uncovers an invisible landscape... 441 00:30:14,605 --> 00:30:17,643 the most energetic regions of the galaxy 442 00:30:17,677 --> 00:30:21,750 highlighted across the sky. 443 00:30:21,785 --> 00:30:23,614 So we pointed the Fermi telescope 444 00:30:23,649 --> 00:30:26,686 towards our very own supermassive black hole, 445 00:30:26,721 --> 00:30:30,414 and we had a picture of what that area sort of looked like... 446 00:30:30,449 --> 00:30:31,450 in our minds, at least. 447 00:30:31,484 --> 00:30:34,522 But then Fermi revealed something 448 00:30:34,556 --> 00:30:37,456 completely astonishing and unexpected. 449 00:30:39,492 --> 00:30:42,944 Emerging from the plane of the Milky Way 450 00:30:42,979 --> 00:30:46,430 are two enormous bubbles, 451 00:30:46,465 --> 00:30:52,436 each one stretching 25,000 light-years, 452 00:30:52,471 --> 00:30:56,613 together reaching half the width of the galaxy. 453 00:30:59,305 --> 00:31:00,962 If you could see in gamma rays, 454 00:31:00,997 --> 00:31:02,446 the Fermi bubbles would be about 455 00:31:02,481 --> 00:31:04,483 the biggest thing you see on the sky. 456 00:31:04,517 --> 00:31:06,485 They look like huge dumbbells 457 00:31:06,519 --> 00:31:07,658 going straight up and straight back 458 00:31:07,693 --> 00:31:12,353 from the center of the black hole. 459 00:31:12,387 --> 00:31:16,115 The bubbles match the imprint scientists expect 460 00:31:16,150 --> 00:31:19,601 an enormous eruption from Sagittarius A-star 461 00:31:19,636 --> 00:31:23,674 to leave on the galaxy. 462 00:31:23,709 --> 00:31:26,919 We had had some clues that the Milky Way might have had 463 00:31:26,954 --> 00:31:29,680 a more energetic and active past, 464 00:31:29,715 --> 00:31:32,028 but the incredible thing about the Fermi bubbles 465 00:31:32,062 --> 00:31:35,790 was that they suddenly gave us concrete evidence 466 00:31:35,824 --> 00:31:38,655 that the Milky Way was much more energetic 467 00:31:38,689 --> 00:31:41,658 at some time in its history. 468 00:31:57,432 --> 00:32:00,642 When our black hole gorges, 469 00:32:00,677 --> 00:32:05,958 it unleashes a towering inferno of super-heated matter. 470 00:32:09,893 --> 00:32:11,343 A supermassive black hole 471 00:32:11,377 --> 00:32:13,932 can impart something like a trillion, 472 00:32:13,966 --> 00:32:16,210 trillion atomic bombs' per second 473 00:32:16,244 --> 00:32:18,246 worth of energy. 474 00:32:18,281 --> 00:32:20,662 If we were to be in the line of fire 475 00:32:20,697 --> 00:32:22,802 of one of those jets, 476 00:32:22,837 --> 00:32:23,942 it would be catastrophic for us. 477 00:32:23,976 --> 00:32:26,599 We'd be vaporized. 478 00:32:40,820 --> 00:32:43,271 Every planet in the jet's path 479 00:32:43,306 --> 00:32:46,412 could have its atmosphere stripped away. 480 00:33:06,881 --> 00:33:08,572 But further out in the galaxy... 481 00:33:12,818 --> 00:33:16,995 these violent outbursts from Sagittarius A-star 482 00:33:17,029 --> 00:33:20,481 may have played a surprising role. 483 00:33:33,942 --> 00:33:39,017 Because the hot gas displaced by the supermassive black hole 484 00:33:39,051 --> 00:33:44,056 has a calming effect on the galaxy that hosts it. 485 00:33:44,091 --> 00:33:45,575 In order for stars to form, 486 00:33:45,609 --> 00:33:49,165 you need very cold and very dense gas, 487 00:33:49,199 --> 00:33:52,340 because stars form through the collapse of material. 488 00:33:52,375 --> 00:33:55,309 So, instead, if you have 489 00:33:55,343 --> 00:33:57,690 something like a supermassive black hole 490 00:33:57,725 --> 00:34:00,555 that is sending out these hot jets 491 00:34:00,590 --> 00:34:02,764 into the galaxy around it, 492 00:34:02,799 --> 00:34:05,698 those jets are going to heat up the gas. 493 00:34:05,733 --> 00:34:08,253 Now the gas is no longer cold enough 494 00:34:08,287 --> 00:34:10,255 to collapse and then form a star. 495 00:34:12,395 --> 00:34:14,742 There's a symbiotic relationship 496 00:34:14,776 --> 00:34:16,882 between the supermassive black hole at the center 497 00:34:16,916 --> 00:34:19,643 and its host galaxy. 498 00:34:19,678 --> 00:34:22,198 And this relationship determines 499 00:34:22,232 --> 00:34:24,959 the rate at which stars form, planets form, 500 00:34:24,993 --> 00:34:27,755 and ultimately, in some sense, 501 00:34:27,789 --> 00:34:29,067 why we are here. 502 00:34:49,777 --> 00:34:52,124 After spending billions of years 503 00:34:52,159 --> 00:34:57,750 consuming the gas, dust, and stars around it, 504 00:34:57,785 --> 00:35:00,891 there is little left to feast on. 505 00:35:05,379 --> 00:35:08,761 Our black hole falls dormant. 506 00:35:11,316 --> 00:35:17,287 Today, the Milky Way has entered an era of calm 507 00:35:17,322 --> 00:35:21,809 and Sagittarius A-star is a sleeping giant, 508 00:35:21,843 --> 00:35:26,124 the enormous bubbles spotted by the Fermi telescope 509 00:35:26,158 --> 00:35:29,057 echoes of a lively past. 510 00:35:29,092 --> 00:35:30,576 You never want to assume that 511 00:35:30,611 --> 00:35:33,234 you live at a special time in the history of the universe. 512 00:35:33,269 --> 00:35:36,272 But it is kind of a special time 513 00:35:36,306 --> 00:35:38,343 that, right now, the black hole is very quiet, 514 00:35:38,377 --> 00:35:40,034 and it must have been much more active 515 00:35:40,068 --> 00:35:43,693 a few million years ago. 516 00:35:47,904 --> 00:35:49,940 As our understanding has grown, 517 00:35:49,975 --> 00:35:54,152 our picture of black holes has transformed, 518 00:35:54,186 --> 00:35:57,672 no longer sinister monsters, 519 00:35:57,707 --> 00:36:00,365 but agents of change and creation. 520 00:36:00,399 --> 00:36:04,231 Sculptors of the cosmos. 521 00:36:04,265 --> 00:36:05,508 We are far from 522 00:36:05,542 --> 00:36:08,062 unlocking all the secrets 523 00:36:08,096 --> 00:36:10,340 of our galaxy's supermassive black hole. 524 00:36:10,375 --> 00:36:12,963 And in fact, the stuff that remains 525 00:36:12,998 --> 00:36:15,103 is probably the most interesting: 526 00:36:15,138 --> 00:36:19,177 what happens inside a supermassive black hole 527 00:36:19,211 --> 00:36:22,007 and at its event horizon. 528 00:36:27,115 --> 00:36:30,981 Black holes challenge the most basic principle 529 00:36:31,016 --> 00:36:34,537 about the predictability of the universe 530 00:36:34,571 --> 00:36:37,436 and the certainty of history. 531 00:36:40,163 --> 00:36:43,822 Nothing could get out of a black hole. 532 00:36:43,856 --> 00:36:45,824 Or so it was thought. 533 00:36:50,829 --> 00:36:52,071 Black holes are where 534 00:36:52,106 --> 00:36:58,181 two of our greatest theories collide and clash. 535 00:36:58,216 --> 00:37:01,115 So you've got these two primal forces in the universe: 536 00:37:01,149 --> 00:37:05,464 gravity, which we all understand and feel with our bones. 537 00:37:05,499 --> 00:37:07,294 And then you've got quantum mechanics, 538 00:37:07,328 --> 00:37:10,504 which governs the theory of the ultra-small, 539 00:37:10,538 --> 00:37:12,299 how atoms and nuclei come together. 540 00:37:12,333 --> 00:37:14,508 The black hole 541 00:37:14,542 --> 00:37:18,132 is where gravity and quantum mechanics finally meet. 542 00:37:18,166 --> 00:37:21,722 SYLVESTER JAMES GATES, JR.: When we try to take the mathematics of the very large 543 00:37:21,756 --> 00:37:23,517 and try to combine that with 544 00:37:23,551 --> 00:37:25,346 the mathematics of the very small, 545 00:37:25,381 --> 00:37:28,142 instead of matching... 546 00:37:28,176 --> 00:37:29,488 They get into a fight. 547 00:37:29,523 --> 00:37:33,216 And so we don't have a consistent way to describe both. 548 00:37:35,391 --> 00:37:38,152 We can begin to probe this deep mystery 549 00:37:38,186 --> 00:37:42,605 by investigating the heart of Sagittarius A-star. 550 00:37:46,540 --> 00:37:52,270 Scientists have studied dozens of stars in its orbit, 551 00:37:52,304 --> 00:37:56,032 some passing just a few billion miles 552 00:37:56,066 --> 00:37:58,862 from the event horizon, 553 00:37:58,897 --> 00:38:03,073 a hair's width on galactic scales. 554 00:38:03,108 --> 00:38:07,526 And these fly-bys could have catastrophic consequences... 555 00:38:16,673 --> 00:38:21,609 because some of these stars likely have planets in orbit. 556 00:38:24,819 --> 00:38:29,617 Planets that may stray too close. 557 00:38:29,652 --> 00:38:32,586 Moths to a flame. 558 00:38:37,107 --> 00:38:39,834 Pulled from their parent stars 559 00:38:39,869 --> 00:38:42,734 towards the abyss. 560 00:38:42,768 --> 00:38:45,046 So imagine you're some alien civilization 561 00:38:45,081 --> 00:38:47,877 looking up at your lovely home star, S2, in the sky. 562 00:38:47,911 --> 00:38:52,088 And one day, the thing starts wandering closer and closer 563 00:38:52,122 --> 00:38:54,504 to what we call the tidal disruption radius 564 00:38:54,539 --> 00:38:55,781 of Sagittarius A-star, 565 00:38:55,816 --> 00:39:00,476 this four-million-solar-mass black hole. 566 00:39:00,510 --> 00:39:02,340 If you fell into a black hole, 567 00:39:02,374 --> 00:39:05,481 you'd pass the event horizon, and actually, 568 00:39:05,515 --> 00:39:07,862 bizarrely, you'd see nothing. 569 00:39:07,897 --> 00:39:13,143 There's no physical barrier, there's no big line in space 570 00:39:13,178 --> 00:39:16,664 saying "point of no return." 571 00:39:16,699 --> 00:39:19,943 You would just drift very casually, gently 572 00:39:19,978 --> 00:39:22,912 across the event horizon. 573 00:39:24,500 --> 00:39:25,984 If we could stand on 574 00:39:26,018 --> 00:39:30,160 such a planet and look outwards, 575 00:39:30,195 --> 00:39:33,612 we'd see something spectacular. 576 00:39:39,825 --> 00:39:42,621 You would see a distorted universe, 577 00:39:42,656 --> 00:39:45,900 and in fact, you'd see it distorted 578 00:39:45,935 --> 00:39:49,904 in both time and space. 579 00:39:49,939 --> 00:39:52,044 You'd see it playing out 580 00:39:52,079 --> 00:39:55,807 at an amazingly fast speed. 581 00:39:55,841 --> 00:39:58,706 The rest of time would play out unbelievably fast 582 00:39:58,741 --> 00:40:00,708 in front of your eyes. 583 00:40:03,573 --> 00:40:07,577 But eventually, tidal and gravitational forces 584 00:40:07,612 --> 00:40:10,615 become too strong... 585 00:40:13,963 --> 00:40:19,037 stretching space and everything in it. 586 00:40:19,071 --> 00:40:21,073 Your feet would be pulled 587 00:40:21,108 --> 00:40:22,765 more strongly by gravity than your head, 588 00:40:22,799 --> 00:40:26,872 so you'd be stretched out into a giant string, 589 00:40:26,907 --> 00:40:31,325 and eventually, you'd be one long string one atom thick. 590 00:40:31,359 --> 00:40:36,019 We call this spaghettification. 591 00:40:36,054 --> 00:40:39,333 Boulders become rocks. 592 00:40:39,367 --> 00:40:41,197 Rocks become sand, 593 00:40:41,231 --> 00:40:43,786 whose very atoms 594 00:40:43,820 --> 00:40:48,998 are then pulled apart. 595 00:40:49,032 --> 00:40:53,761 Gravity and the quantum world collide. 596 00:40:53,796 --> 00:40:57,489 Ahead, the heart of the black hole... 597 00:40:57,524 --> 00:41:00,803 the singularity, 598 00:41:00,837 --> 00:41:05,152 where all journeys in terminate. 599 00:41:05,186 --> 00:41:06,533 Our idea of a singularity 600 00:41:06,567 --> 00:41:08,293 is that everything is compressed 601 00:41:08,327 --> 00:41:11,261 beyond what it can be until it's nothing, 602 00:41:11,296 --> 00:41:13,263 but yet still exists. 603 00:41:13,298 --> 00:41:15,507 That is... 604 00:41:15,542 --> 00:41:18,027 Wow. 605 00:41:41,153 --> 00:41:42,948 Over trillions of years, 606 00:41:42,983 --> 00:41:46,089 all the stars around Sagittarius A-star 607 00:41:46,124 --> 00:41:49,714 will gradually fade out of existence. 608 00:42:01,588 --> 00:42:05,039 Long after the last-ever sun sets on any planet, 609 00:42:05,074 --> 00:42:06,972 black holes will continue to roam the universe. 610 00:42:14,290 --> 00:42:16,810 The final dark age. 611 00:42:23,230 --> 00:42:24,334 If nothing can ever escape, 612 00:42:24,369 --> 00:42:26,647 if this is some eternal prison, 613 00:42:26,682 --> 00:42:28,269 is that the end of the story? 614 00:42:31,963 --> 00:42:33,827 Perhaps not. 615 00:42:33,861 --> 00:42:37,071 Because scientists now believe that even 616 00:42:37,106 --> 00:42:39,557 Sagittarius A-star will die. 617 00:42:45,183 --> 00:42:48,945 And its death will come at the hands of 618 00:42:48,980 --> 00:42:52,328 what might seem an inconsequential effect 619 00:42:52,362 --> 00:42:55,883 first described almost five decades ago. 620 00:42:57,436 --> 00:42:58,783 So in 1975, 621 00:42:58,817 --> 00:43:02,165 Stephen Hawking published this amazing paper 622 00:43:02,200 --> 00:43:07,619 showing that black holes aren't absolutely, completely black. 623 00:43:07,654 --> 00:43:10,933 They glow very, very faintly. 624 00:43:10,967 --> 00:43:15,627 They have a temperature associated with them. 625 00:43:15,662 --> 00:43:18,561 And you can write that temperature 626 00:43:18,596 --> 00:43:24,256 very simply in an equation 627 00:43:24,291 --> 00:43:25,637 that's just beautiful. 628 00:43:25,672 --> 00:43:28,744 It links together so many different parts of physics. 629 00:43:28,778 --> 00:43:30,262 It's got gravity in it. 630 00:43:30,297 --> 00:43:32,644 It's got the mass of the black hole in it. 631 00:43:32,679 --> 00:43:34,646 It's got the speed of light. 632 00:43:34,681 --> 00:43:37,511 It's got constants relating to atomic physics, 633 00:43:37,545 --> 00:43:39,030 the microworld. 634 00:43:39,064 --> 00:43:42,550 And it's putting all of these together 635 00:43:42,585 --> 00:43:44,518 and giving us a temperature. 636 00:43:44,552 --> 00:43:47,832 Hawking's equation has huge implications 637 00:43:47,866 --> 00:43:50,455 for the future of the black hole. 638 00:43:50,489 --> 00:43:52,733 So if something has a temperature, 639 00:43:52,768 --> 00:43:54,839 it's glowing, it's radiating. 640 00:43:54,873 --> 00:43:56,737 Like when you put your hand close to a fire, 641 00:43:56,772 --> 00:43:57,738 you can feel it. 642 00:43:57,773 --> 00:44:00,638 And that losing energy, 643 00:44:00,672 --> 00:44:03,606 for a black hole like Sagittarius A-star, 644 00:44:03,641 --> 00:44:06,436 over timescales that are hugely long, 645 00:44:06,471 --> 00:44:10,751 it's going to evaporate away. 646 00:44:10,786 --> 00:44:13,651 It's going to disappear. 647 00:44:26,836 --> 00:44:28,907 Very gradually, 648 00:44:28,942 --> 00:44:31,047 this Hawking radiation 649 00:44:31,082 --> 00:44:36,639 will erode away Sagittarius A-star 650 00:44:36,674 --> 00:44:40,919 until, many trillions and trillions of years 651 00:44:40,954 --> 00:44:43,059 into the future... 652 00:44:49,894 --> 00:44:52,828 in a final burst of light... 653 00:44:57,729 --> 00:45:03,217 our black hole will disappear. 654 00:45:03,252 --> 00:45:06,773 And then the Milky Way will be completely dark 655 00:45:06,807 --> 00:45:09,776 for all eternity. 656 00:45:12,606 --> 00:45:13,952 So why does it matter 657 00:45:13,987 --> 00:45:15,782 if these black holes disintegrate 658 00:45:15,816 --> 00:45:18,854 in the far distant future? 659 00:45:18,888 --> 00:45:22,547 Well, the discovery of Hawking radiation 660 00:45:22,581 --> 00:45:25,653 raised some profound questions in physics. 661 00:45:25,688 --> 00:45:28,691 If I was to set fire to this piece of paper 662 00:45:28,726 --> 00:45:31,832 with Stephen Hawking's equation written on it... 663 00:45:33,972 --> 00:45:37,044 what happens to all that information as it burns away, 664 00:45:37,079 --> 00:45:39,322 as it radiates away? 665 00:45:39,357 --> 00:45:45,466 Do we lose it from the universe forever? 666 00:45:56,823 --> 00:46:01,897 Maybe if I could sweep up all the ash, 667 00:46:01,931 --> 00:46:05,866 if I could find all the photons 668 00:46:05,901 --> 00:46:08,973 and reconstruct them, 669 00:46:09,007 --> 00:46:12,942 maybe I could reconstruct that piece of paper, 670 00:46:12,977 --> 00:46:17,119 even the equation written on it. 671 00:46:17,153 --> 00:46:20,087 So does this also apply to black holes? 672 00:46:20,122 --> 00:46:23,366 What happened to all the information 673 00:46:23,401 --> 00:46:25,472 contained on all the material 674 00:46:25,506 --> 00:46:27,405 that ever fell into a black hole? 675 00:46:27,439 --> 00:46:32,755 And as a black hole evaporates, what happens to it? 676 00:46:38,830 --> 00:46:43,352 Black holes ain't as black as they are painted. 677 00:46:43,386 --> 00:46:47,770 They are not the eternal prisons they were once thought. 678 00:46:51,291 --> 00:46:56,779 So if you feel you are in a black hole, don't give up. 679 00:47:00,162 --> 00:47:02,820 There's a way out. 680 00:47:09,205 --> 00:47:13,347 If information somehow escapes from Sagittarius A-star 681 00:47:13,382 --> 00:47:15,384 as it evaporates away, 682 00:47:15,418 --> 00:47:19,595 the implication is profound. 683 00:47:19,629 --> 00:47:23,081 Scientists now believe that every star, 684 00:47:23,116 --> 00:47:25,083 asteroid, 685 00:47:25,118 --> 00:47:26,533 planet... 686 00:47:26,567 --> 00:47:30,986 everything that ever fell into Sagittarius A-star... 687 00:47:31,020 --> 00:47:34,023 may live on, 688 00:47:34,058 --> 00:47:36,336 every aspect and position 689 00:47:36,370 --> 00:47:41,582 of every particle encoded as information. 690 00:47:43,308 --> 00:47:45,552 All that you would theoretically need 691 00:47:45,586 --> 00:47:48,589 to put the whole back together. 692 00:47:50,764 --> 00:47:53,180 So the memory of every single thing 693 00:47:53,215 --> 00:47:55,217 that's "fallen into," become part of, 694 00:47:55,251 --> 00:47:56,804 Sagittarius A-star in the Milky Way 695 00:47:56,839 --> 00:47:57,875 hasn't been lost. 696 00:47:57,909 --> 00:47:59,462 It's still there. 697 00:47:59,497 --> 00:48:02,293 It's just that we can't access that now. 698 00:48:02,327 --> 00:48:06,918 But maybe we might be able to read the ashes of that memory 699 00:48:06,953 --> 00:48:10,094 in the far future of the universe. 700 00:48:10,128 --> 00:48:15,133 But how can anything escape a black hole's grip? 701 00:48:15,168 --> 00:48:17,066 The defining fact of a black hole 702 00:48:17,101 --> 00:48:19,482 is that nothing should be able to get out. 703 00:48:19,517 --> 00:48:22,278 And yet when you look at Hawking radiation, 704 00:48:22,313 --> 00:48:25,074 it seems to be suggesting that quantum physics 705 00:48:25,109 --> 00:48:29,285 does connect up the inside back to the outside. 706 00:48:29,320 --> 00:48:34,256 We just don't really know how. 707 00:48:34,290 --> 00:48:36,637 Black holes force us to 708 00:48:36,672 --> 00:48:42,264 consider nature in entirely new and mind-bending ways. 709 00:48:42,298 --> 00:48:45,060 People aren't at all certain about the resolution 710 00:48:45,094 --> 00:48:48,511 to what happens when we throw things into black holes, 711 00:48:48,546 --> 00:48:49,685 as far as where the information goes. 712 00:48:49,719 --> 00:48:51,031 It's still an open question. 713 00:48:51,066 --> 00:48:53,827 Maybe it gets sent to a portal to another dimension, 714 00:48:53,861 --> 00:48:56,692 maybe it gets pumped into some other branch 715 00:48:56,726 --> 00:48:59,315 of a larger multiverse. 716 00:48:59,350 --> 00:49:01,386 Some people imagine that black holes are really 717 00:49:01,421 --> 00:49:05,045 just a kind of quantum fuzz, a fuzzball. 718 00:49:05,080 --> 00:49:06,978 Some people think that all the information 719 00:49:07,013 --> 00:49:08,255 that fell into the black hole 720 00:49:08,290 --> 00:49:09,981 is somehow encoded on its surface 721 00:49:10,016 --> 00:49:12,225 in a hologram. 722 00:49:12,259 --> 00:49:15,021 But we're not really privy to any of this information. 723 00:49:15,055 --> 00:49:17,092 And if we want to find out, we'd have to go in. 724 00:49:19,473 --> 00:49:21,993 Whatever the solution proves to be, 725 00:49:22,028 --> 00:49:23,891 it will have ramifications 726 00:49:23,926 --> 00:49:27,585 far beyond the black hole itself. 727 00:49:30,726 --> 00:49:35,110 This theory of quantum gravity that's so elusive right now, 728 00:49:35,144 --> 00:49:36,870 that is what we would need to describe 729 00:49:36,904 --> 00:49:40,011 what's happening inside black holes, 730 00:49:40,046 --> 00:49:42,324 could either be the most exciting development 731 00:49:42,358 --> 00:49:47,156 to happen in the next decade or maybe even the next century, 732 00:49:47,191 --> 00:49:50,642 or it could be an alarm bell going off in our heads 733 00:49:50,677 --> 00:49:53,024 that maybe Einstein's theory of gravity 734 00:49:53,059 --> 00:49:57,339 is not the final word on gravity. 735 00:49:57,373 --> 00:49:59,927 Solving the mystery of black holes 736 00:49:59,962 --> 00:50:04,587 may be our best chance to complete the picture of nature 737 00:50:04,622 --> 00:50:07,866 that has eluded us for the last century. 738 00:50:07,901 --> 00:50:09,006 So perhaps the important thing 739 00:50:09,040 --> 00:50:11,387 isn't what the answer turns out to be. 740 00:50:11,422 --> 00:50:13,493 The important thing is that we will gain 741 00:50:13,527 --> 00:50:15,288 a fuller understanding of the cosmos 742 00:50:15,322 --> 00:50:16,737 by studying these remarkable objects. 743 00:50:16,772 --> 00:50:21,570 Studying the universe has completely changed our universe. 744 00:50:21,604 --> 00:50:25,436 We have to rethink everything over and over again. 745 00:50:25,470 --> 00:50:27,955 Like, it's almost, like, tear up the universe we know 746 00:50:27,990 --> 00:50:31,890 and write a new one. 747 00:50:31,925 --> 00:50:33,996 We're still a long way from 748 00:50:34,031 --> 00:50:38,966 fully comprehending the secrets of black holes, 749 00:50:39,001 --> 00:50:41,659 but we're beginning to lift the veil. 750 00:50:45,180 --> 00:50:49,011 Far from being mere cosmic aberrations, 751 00:50:49,046 --> 00:50:54,396 black holes fundamentally shape our universe. 752 00:50:56,605 --> 00:50:57,813 So it's extraordinary to think that 753 00:50:57,847 --> 00:50:59,332 we might be fundamentally connected 754 00:50:59,366 --> 00:51:01,265 to something that we didn't know existed 755 00:51:01,299 --> 00:51:03,681 for the vast span of human history. 756 00:51:07,236 --> 00:51:08,962 The beautiful thing about black holes 757 00:51:08,996 --> 00:51:11,344 is that they're such a rich source of information. 758 00:51:11,378 --> 00:51:14,174 We've learned so much about the universe 759 00:51:14,209 --> 00:51:15,900 from studying black holes: 760 00:51:15,934 --> 00:51:17,557 space, time, 761 00:51:17,591 --> 00:51:19,800 the very fundamental nature of reality. 762 00:51:21,423 --> 00:51:23,735 Bit by bit revealing 763 00:51:23,770 --> 00:51:27,636 the deepest mysteries of the cosmos. 764 00:51:27,670 --> 00:51:31,053 We're in a golden age of discovery about black holes. 765 00:51:31,088 --> 00:51:33,055 We understand how they merge, 766 00:51:33,090 --> 00:51:35,644 we've discovered their colossal jets, 767 00:51:35,678 --> 00:51:37,266 and we're beginning to see them 768 00:51:37,301 --> 00:51:41,132 not just as destroyers, but also as creators 769 00:51:41,167 --> 00:51:43,583 and sculptors. 770 00:51:43,617 --> 00:51:46,758 And all that is just the beginning. 771 00:51:46,793 --> 00:51:48,622 Our story's happening now, 772 00:51:48,657 --> 00:51:51,798 but black holes, they're going to outlive us 773 00:51:51,832 --> 00:51:54,041 by trillions of years. 774 00:51:54,076 --> 00:51:57,114 Their story is just getting started. 60254

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