﻿1 00:00:04,504 --> 00:00:05,839 Out in space, 2 00:00:05,839 --> 00:00:07,674 there are places where gravity's 3 00:00:07,674 --> 00:00:09,843 influence is so intense 4 00:00:09,926 --> 00:00:13,096 that not even light can escape. 5 00:00:13,513 --> 00:00:15,849 These are known as black holes, 6 00:00:15,849 --> 00:00:18,476 objects with extreme gravity 7 00:00:18,476 --> 00:00:20,729 caused by extreme density 8 00:00:20,937 --> 00:00:26,192 that have an extreme influence on everything that gets too close. 9 00:00:26,735 --> 00:00:29,070 Often the subject of science fiction 10 00:00:29,070 --> 00:00:31,573 black holes are science fact, 11 00:00:31,573 --> 00:00:34,159 but they're often misunderstood 12 00:00:34,242 --> 00:00:38,705 as black holes aren't exactly holes. 13 00:00:38,788 --> 00:00:40,749 So let's investigate. 14 00:00:40,749 --> 00:00:43,710 What are black holes? 15 00:00:46,087 --> 00:00:49,090 A black hole is an object so compact 16 00:00:49,132 --> 00:00:53,094 that not even light can escape its gravitational potential. 17 00:00:53,136 --> 00:00:54,554 That's exactly where the name 18 00:00:54,554 --> 00:00:55,722 “black hole” comes from. 19 00:00:55,722 --> 00:00:57,557 It's black because it emits no light, 20 00:00:58,183 --> 00:01:00,727 Black holes used to be just a mathematical curiosity. 21 00:01:00,727 --> 00:01:04,481 But in the 1950s, 1960s, we actually realized they're out there 22 00:01:04,731 --> 00:01:06,357 in the universe. 23 00:01:06,357 --> 00:01:07,609 We know that there are black holes 24 00:01:07,609 --> 00:01:09,235 that have stellar masses 25 00:01:09,235 --> 00:01:11,571 that are born from the gravitational 26 00:01:11,571 --> 00:01:14,032 collapse from the death of stars. 27 00:01:14,115 --> 00:01:17,118 We also know that there are much bigger black holes 28 00:01:17,118 --> 00:01:19,496 that sit at the center of galaxies. 29 00:01:19,496 --> 00:01:21,039 The critical thing to remember 30 00:01:21,039 --> 00:01:22,665 about what happens with anything 31 00:01:22,665 --> 00:01:24,334 that's near a black hole 32 00:01:24,334 --> 00:01:27,170 is that black holes don't suck. 33 00:01:27,253 --> 00:01:30,924 You can orbit a black hole just as you can orbit any other star 34 00:01:30,924 --> 00:01:32,842 or any other massive object. 35 00:01:32,842 --> 00:01:35,512 Because there's so much mass in such a tiny volume, 36 00:01:35,595 --> 00:01:38,473 you can get a lot closer to all of that mass. 37 00:01:38,473 --> 00:01:42,644 As matter falls in towards a black hole, it starts spinning faster and faster, 38 00:01:42,644 --> 00:01:44,979 and will naturally form into a disk. 39 00:01:45,063 --> 00:01:48,358 We call it this accretion disk because that matter will accrete 40 00:01:48,358 --> 00:01:49,859 onto the black hole 41 00:01:49,859 --> 00:01:53,988 and that disk get incredibly hot, incredibly bright. 42 00:01:54,072 --> 00:01:54,948 A couple of years ago, 43 00:01:54,948 --> 00:01:57,367 we had the first image of a black hole 44 00:01:57,367 --> 00:01:59,119 and that looked like a donut. 45 00:01:59,160 --> 00:02:01,538 But the donut was the matter around the black hole, 46 00:02:01,538 --> 00:02:03,790 and the black hole itself was just a dark, 47 00:02:03,790 --> 00:02:06,376 you know, ominous void at the center. 48 00:02:06,960 --> 00:02:10,421 Black holes have extreme physics going on around them. 49 00:02:10,630 --> 00:02:12,674 All sorts of crazy things happening. 50 00:02:12,674 --> 00:02:13,633 Your perception 51 00:02:13,633 --> 00:02:18,096 when you got very close to a black hole is that time is slowing down. 52 00:02:18,179 --> 00:02:20,890 If a human traveler got too close to a black hole, 53 00:02:20,890 --> 00:02:23,977 they would first fall through feeling nothing 54 00:02:23,977 --> 00:02:26,729 until the point of spaghettification 55 00:02:26,729 --> 00:02:29,190 where they would be stretched into a cosmic noodle. 56 00:02:29,440 --> 00:02:32,318 When a star is passing by a black hole, 57 00:02:32,318 --> 00:02:34,863 one side of it gets greater gravity than the other. 58 00:02:34,863 --> 00:02:37,490 And so you get this very stretching effect. 59 00:02:37,490 --> 00:02:39,617 And so the star can be torn apart. 60 00:02:39,701 --> 00:02:42,871 This is what's called a tidal disruption event. 61 00:02:42,954 --> 00:02:45,081 What could be inside of a black hole? 62 00:02:45,081 --> 00:02:49,085 The most commonly accepted answer is a point 63 00:02:49,085 --> 00:02:53,339 of infinite density that we cannot really describe well. 64 00:02:53,923 --> 00:02:57,010 At this particular region within a black hole, 65 00:02:57,093 --> 00:03:01,014 all of our theory of general relativity breaks down. 66 00:03:02,015 --> 00:03:04,309 There's all sorts of ways of finding black holes. 67 00:03:04,309 --> 00:03:06,853 You can find them from their emission at 68 00:03:06,853 --> 00:03:08,980 certain wavelengths, like in the x-rays. 69 00:03:09,230 --> 00:03:11,024 We can see them in the optical, 70 00:03:11,024 --> 00:03:13,193 in the ultraviolet, in the infrared. 71 00:03:13,276 --> 00:03:17,030 Various NASA missions have been great at finding black holes. 72 00:03:17,113 --> 00:03:17,947 And then more recently, 73 00:03:17,947 --> 00:03:19,866 the really exciting way to find black holes 74 00:03:19,866 --> 00:03:22,160 is when two black holes merge, 75 00:03:22,243 --> 00:03:25,163 they create ripples in spacetime and you can detect that 76 00:03:25,163 --> 00:03:28,124 from gravitational wave observatories. 77 00:03:29,000 --> 00:03:31,753 One big mystery about astronomical black holes 78 00:03:31,753 --> 00:03:35,715 is how the large supermassive black holes that exist 79 00:03:35,715 --> 00:03:39,928 at the center of almost every galaxy actually go to be there. 80 00:03:40,094 --> 00:03:44,224 Another critical question is really what happens beyond the event horizon? 81 00:03:44,474 --> 00:03:47,977 What is essentially inside the black hole? 82 00:03:48,061 --> 00:03:50,063 The real reason we want to know about these, 83 00:03:50,063 --> 00:03:52,065 as interesting as they are on their own, 84 00:03:52,148 --> 00:03:53,316 they're all connected 85 00:03:53,316 --> 00:03:57,487 with our general understanding of the physics of the universe. 86 00:03:57,570 --> 00:04:01,032 We're seeing black holes bigger than we had seen before. 87 00:04:01,032 --> 00:04:05,245 We're seeing black holes that way a hundred times the mass of the sun. 88 00:04:05,328 --> 00:04:09,123 And right now the community is trying to figure out where they're created. 89 00:04:10,291 --> 00:04:12,669 Einstein himself did not think such things would exist. 90 00:04:12,669 --> 00:04:16,297 Other people using his theory said, “We could have things like this, 91 00:04:16,381 --> 00:04:17,715 like black holes.” 92 00:04:17,715 --> 00:04:21,469 And now it's become sort of a bread and butter kind of study 93 00:04:21,469 --> 00:04:23,137 on many levels 94 00:04:23,137 --> 00:04:25,848 to the point of us imaging them directly. 95 00:04:26,808 --> 00:04:28,059 I think it's one of the 96 00:04:28,059 --> 00:04:31,104 great stories of how science works 97 00:04:31,437 --> 00:04:33,481 From pursuing ideas 98 00:04:33,481 --> 00:04:35,024 in terms of purely theoretical thought, 99 00:04:35,024 --> 00:04:36,901 but then observations coming in 100 00:04:36,901 --> 00:04:38,361 and then merging the two 101 00:04:38,444 --> 00:04:40,905 to have a better understanding of the universe. 102 00:04:42,782 --> 00:04:44,909 The first black hole ever confirmed, 103 00:04:44,909 --> 00:04:46,327 Cygnus X-1, 104 00:04:46,327 --> 00:04:49,789 was first discovered back in 1964 105 00:04:49,872 --> 00:04:53,001 when astronomers identified high energy x-rays 106 00:04:53,001 --> 00:04:55,670 captured by a sounding rocket. 107 00:04:55,753 --> 00:04:58,840 Since then, NASA has launched a number of different 108 00:04:58,840 --> 00:05:02,844 missions and studies to further investigate black holes. 109 00:05:02,927 --> 00:05:08,391 These have included NASA's Chandra X-ray Observatory, the Hubble Space Telescope, 110 00:05:08,474 --> 00:05:13,146 NuStar, the James Webb Space Telescope, and many more. 111 00:05:13,813 --> 00:05:17,817 These are just a few examples of NASA's continued efforts 112 00:05:18,026 --> 00:05:22,071 to expand our understanding of black holes. 113 00:05:22,155 --> 00:05:25,950 Thankfully, as humans living on planet Earth, 114 00:05:26,034 --> 00:05:29,746 we will never be close enough to any black hole, 115 00:05:29,954 --> 00:05:33,708 including the supermassive a black hole at the center of our own galaxy 116 00:05:33,791 --> 00:05:37,628 to ever be in danger of falling in. 117 00:05:37,712 --> 00:05:38,880 I promise.