1 00:00:02,203 --> 00:00:06,005 Narrator: 26,000 light-years from earth, 2 00:00:06,007 --> 00:00:10,376 shrouded in cosmic dust and gas 3 00:00:10,378 --> 00:00:13,679 is a mysterious region of space -- 4 00:00:13,681 --> 00:00:17,282 the center of the milky way. 5 00:00:17,284 --> 00:00:22,454 The center of the milky way galaxy is one of the strangest, 6 00:00:22,456 --> 00:00:28,227 most exotic and violent places in our galaxy. 7 00:00:29,563 --> 00:00:30,996 Plait: Gas streaming everywhere, 8 00:00:30,998 --> 00:00:33,966 radiation blasting out, 9 00:00:33,968 --> 00:00:36,869 stars moving willy-nilly. 10 00:00:36,871 --> 00:00:39,905 Thaller: And at the very heart is the mysterious black hole, 11 00:00:39,907 --> 00:00:43,409 4 million times the mass of the sun. 12 00:00:43,411 --> 00:00:46,945 Narrator: Now we're exploring the center of the milky way 13 00:00:46,947 --> 00:00:49,948 like never before, 14 00:00:49,950 --> 00:00:55,621 uncovering powerful forces that affect us all. 15 00:00:55,623 --> 00:00:58,057 Everything that happens at the center of the milky way galaxy 16 00:00:58,059 --> 00:00:59,992 really is connected to what's going on 17 00:00:59,994 --> 00:01:02,261 in the rest of the milky way. 18 00:01:02,263 --> 00:01:04,930 Narrator: Understanding the center of our galaxy 19 00:01:04,932 --> 00:01:10,803 unlock secrets of our past, present and future. 20 00:01:10,805 --> 00:01:13,806 -- Captions by vitac -- www.Vitac.Com 21 00:01:13,808 --> 00:01:16,809 captions paid for by discovery communications 22 00:01:16,811 --> 00:01:22,081 ♪ 23 00:01:22,083 --> 00:01:27,386 ♪ 24 00:01:27,388 --> 00:01:30,622 March 2019. 25 00:01:30,624 --> 00:01:34,226 We focus the xmm-newton space telescope 26 00:01:34,228 --> 00:01:39,665 on a region of space around sagittarius a-star, 27 00:01:39,667 --> 00:01:43,368 the supermassive black hole at the heart of our galaxy. 28 00:01:47,441 --> 00:01:53,011 We spot two huge columns of gas glowing in x-ray light. 29 00:01:53,013 --> 00:01:59,818 ♪ 30 00:01:59,820 --> 00:02:03,922 the columns seem to be coming from sagittarius a-star. 31 00:02:06,026 --> 00:02:08,293 Filippenko: We see giant fountains of gas 32 00:02:08,295 --> 00:02:11,563 extending outward from the central region 33 00:02:11,565 --> 00:02:15,501 as though it's like a wind or a giant expulsion event. 34 00:02:17,471 --> 00:02:21,640 Narrator: The fountains of gas extend 500 light-years above 35 00:02:21,642 --> 00:02:24,810 and below the supermassive black hole. 36 00:02:27,648 --> 00:02:30,215 That's over a million times the distance 37 00:02:30,217 --> 00:02:32,384 from the sun to neptune. 38 00:02:35,189 --> 00:02:36,488 It looks like this material 39 00:02:36,490 --> 00:02:38,991 is actually leaving the vicinity of the black hole, 40 00:02:38,993 --> 00:02:44,463 like it's burping out these giant, hot x-ray chimneys. 41 00:02:44,465 --> 00:02:48,834 Narrator: So why is sagittarius a-star burping out hot gas? 42 00:02:50,371 --> 00:02:53,071 Typically, around a black hole, you have an accretion disk 43 00:02:53,073 --> 00:02:54,940 funneling material into the black hole, 44 00:02:54,942 --> 00:02:57,309 but all of it doesn't end up in the black hole. 45 00:02:59,413 --> 00:03:01,213 Tremblay: There is a little bit of gas 46 00:03:01,215 --> 00:03:03,615 falling onto it right now, even as I'm speaking, right? 47 00:03:05,653 --> 00:03:08,520 As gas falls toward the supermassive black hole, 48 00:03:08,522 --> 00:03:09,855 it becomes super heated. 49 00:03:09,857 --> 00:03:12,558 It liberates an enormous amount of energy 50 00:03:12,560 --> 00:03:16,328 and that energy has to go somewhere. 51 00:03:16,330 --> 00:03:20,032 Narrator: As gas spirals towards the black hole, 52 00:03:20,034 --> 00:03:25,537 some of the material accelerates to near the speed of light. 53 00:03:25,539 --> 00:03:28,073 It blasts out from the accretion disk... 54 00:03:30,678 --> 00:03:34,146 ...Creating chimneys of superheated gas 55 00:03:34,148 --> 00:03:35,714 that seem to connect 56 00:03:35,716 --> 00:03:38,650 to two of the largest structures in the galaxy -- 57 00:03:38,652 --> 00:03:42,854 the milky way's fermi bubbles. 58 00:03:42,856 --> 00:03:44,623 A few years ago, we noticed that, in fact, 59 00:03:44,625 --> 00:03:47,726 there are these giant bubbles coming out of the very heart 60 00:03:47,728 --> 00:03:49,428 of the milky way galaxy. 61 00:03:49,430 --> 00:03:50,429 In each direction, 62 00:03:50,431 --> 00:03:54,900 there's a bubble 25,000 light-years long. 63 00:03:54,902 --> 00:03:56,768 Narrator: But the gas-filled bubbles 64 00:03:56,770 --> 00:03:59,871 dwarf the chimneys of superheated gas. 65 00:03:59,873 --> 00:04:04,209 Scientists wonder if another more powerful force 66 00:04:04,211 --> 00:04:06,278 blew the bubbles. 67 00:04:06,280 --> 00:04:09,114 So what could have created all of this superheated gas 68 00:04:09,116 --> 00:04:12,551 that actually blew these tremendously large bubbles? 69 00:04:12,553 --> 00:04:16,054 Narrator: Supermassive black holes in other galaxies 70 00:04:16,056 --> 00:04:18,123 might offer clues. 71 00:04:18,125 --> 00:04:19,791 Black holes at the centers of galaxies 72 00:04:19,793 --> 00:04:21,126 go through different phases. 73 00:04:21,128 --> 00:04:25,664 So they can be either active or they can be calm. 74 00:04:25,666 --> 00:04:28,033 Sometimes black holes at the centers of galaxies 75 00:04:28,035 --> 00:04:30,435 go through an active phase. 76 00:04:30,437 --> 00:04:32,437 And when that happens, 77 00:04:32,439 --> 00:04:35,407 the black hole is actively feeding on material around it, 78 00:04:35,409 --> 00:04:36,908 which means it's growing 79 00:04:36,910 --> 00:04:40,078 and it also gives off huge jets of radiation. 80 00:04:42,483 --> 00:04:45,183 Narrator: Calm supermassive black holes 81 00:04:45,185 --> 00:04:47,119 release a trickle of hot gas. 82 00:04:51,158 --> 00:04:55,160 But when lots of material falls on them, 83 00:04:55,162 --> 00:04:59,131 they can shoot out jets up to millions of light-years long. 84 00:04:59,133 --> 00:05:04,102 ♪ 85 00:05:04,104 --> 00:05:05,337 at the current time, 86 00:05:05,339 --> 00:05:07,939 sagittarius a-star is what we call quiescent. 87 00:05:07,941 --> 00:05:09,141 It's quiet. 88 00:05:09,143 --> 00:05:11,276 There is some material swirling around it, 89 00:05:11,278 --> 00:05:14,179 but really not very much. 90 00:05:14,181 --> 00:05:16,748 But we don't think that's always been the case. 91 00:05:19,086 --> 00:05:21,820 The centers of galaxies are busy places. 92 00:05:21,822 --> 00:05:24,389 There are stars there. There's gas there. 93 00:05:24,391 --> 00:05:25,724 There's dust there, 94 00:05:25,726 --> 00:05:29,194 and sometimes these things fall into that black hole. 95 00:05:32,166 --> 00:05:34,066 Narrator: 6 million years ago, 96 00:05:34,068 --> 00:05:37,736 sagittarius a-star may have had a feeding frenzy... 97 00:05:40,307 --> 00:05:42,107 ...Eating too much 98 00:05:42,109 --> 00:05:45,377 and blasting out the remains in huge jets. 99 00:05:49,483 --> 00:05:51,616 Those jets plow through the galaxy 100 00:05:51,618 --> 00:05:55,754 initially at near the speed of light. 101 00:05:55,756 --> 00:05:57,723 And as they do so, they can wreak havoc 102 00:05:57,725 --> 00:06:00,292 or sculpt the evolution of the galaxy 103 00:06:00,294 --> 00:06:01,693 that they're propagating through. 104 00:06:03,897 --> 00:06:06,298 Narrator: Sagittarius a-star's jets 105 00:06:06,300 --> 00:06:09,568 blasted gas out of the galaxy, 106 00:06:09,570 --> 00:06:14,606 creating the scars we see as the fermi bubbles. 107 00:06:14,608 --> 00:06:17,642 Now, whatever caused those jets seems to have turned off. 108 00:06:17,644 --> 00:06:18,977 It's not happening anymore 109 00:06:18,979 --> 00:06:23,048 and we're seeing sort of the leftovers of them. 110 00:06:23,050 --> 00:06:24,316 But this is clearly a sign 111 00:06:24,318 --> 00:06:26,518 that sometime in the past few million years, 112 00:06:26,520 --> 00:06:28,286 the black hole in the center of our galaxy, 113 00:06:28,288 --> 00:06:32,958 sagittarius a-star, was actively feeding on material around it. 114 00:06:35,396 --> 00:06:39,164 Material was falling into it and blasting out this stuff. 115 00:06:42,069 --> 00:06:45,036 Narrator: The jets left destruction in their wake. 116 00:06:45,038 --> 00:06:50,075 ♪ 117 00:06:50,077 --> 00:06:55,480 they may have also affected the growth of our entire galaxy. 118 00:06:55,482 --> 00:06:58,283 These structures at the center of our galaxy are important 119 00:06:58,285 --> 00:07:01,119 because they can either shut off star formation 120 00:07:01,121 --> 00:07:03,321 or they can trigger star formation. 121 00:07:06,226 --> 00:07:09,127 Tremblay: As those jets propagate through the galaxy, 122 00:07:09,129 --> 00:07:10,462 they pile up gas 123 00:07:10,464 --> 00:07:13,131 and that gas can be then triggered into star formation. 124 00:07:16,437 --> 00:07:21,006 But these jets can also impart so much heat or energy feedback 125 00:07:21,008 --> 00:07:23,742 into the environment that they prevent star formation. 126 00:07:27,114 --> 00:07:30,015 So black holes in many ways conduct an orchestra, 127 00:07:30,017 --> 00:07:34,419 instructing or dictating when stars can and cannot form. 128 00:07:34,421 --> 00:07:43,028 ♪ 129 00:07:43,030 --> 00:07:45,197 narrator: In the center of the milky way, 130 00:07:45,199 --> 00:07:47,566 star-formation rates seem low. 131 00:07:50,003 --> 00:07:52,737 The jets could be responsible. 132 00:07:54,074 --> 00:07:58,043 But in 2017, the alma telescope discovered 133 00:07:58,045 --> 00:08:00,679 that change is coming. 134 00:08:02,549 --> 00:08:05,183 Thaller: So alma's actually been able to peer in 135 00:08:05,185 --> 00:08:06,551 to the heart of our galaxy 136 00:08:06,553 --> 00:08:10,522 and see that near all this destruction, 137 00:08:10,524 --> 00:08:13,525 there might actually be a new generation of stars forming. 138 00:08:15,662 --> 00:08:18,797 Narrator: Today, our calm supermassive black hole 139 00:08:18,799 --> 00:08:21,833 could be helping star formation in the core. 140 00:08:24,972 --> 00:08:28,573 But the fermi bubbles could be evidence of a time 141 00:08:28,575 --> 00:08:34,045 when sagittarius a-star shut down star formation. 142 00:08:34,047 --> 00:08:35,947 Could the supermassive black hole 143 00:08:35,949 --> 00:08:39,417 roar back to life in the future? 144 00:08:39,419 --> 00:08:41,720 Tremblay: Sagittarius a-star could roar back to life 145 00:08:41,722 --> 00:08:43,922 by just dumping some gas onto it. 146 00:08:43,924 --> 00:08:46,424 And there's a lot of gas at the center of our galaxy 147 00:08:46,426 --> 00:08:48,426 and it could wander into the proximity 148 00:08:48,428 --> 00:08:49,761 of sagittarius a-star 149 00:08:49,763 --> 00:08:51,897 and ultimately fall onto the event horizon 150 00:08:51,899 --> 00:08:53,532 and that would light it up. 151 00:08:58,071 --> 00:09:01,840 Narrator: If sagittarius a-star eats enough gas... 152 00:09:04,678 --> 00:09:07,379 ...It could shut down star formation in the galaxy 153 00:09:07,381 --> 00:09:09,114 for millions of years. 154 00:09:09,116 --> 00:09:14,986 ♪ 155 00:09:14,988 --> 00:09:18,557 it could also give off x-rays and gamma rays 156 00:09:18,559 --> 00:09:20,191 that may hit the earth. 157 00:09:23,797 --> 00:09:27,365 Sutter: Thankfully, our central supermassive black hole 158 00:09:27,367 --> 00:09:30,769 is pretty quiet and massive feeding events, 159 00:09:30,771 --> 00:09:34,005 massive energy events are very, very rare. 160 00:09:35,909 --> 00:09:38,977 We don't necessarily have much to worry about. 161 00:09:41,381 --> 00:09:45,050 Narrator: Sagittarius a-star has reshaped our galaxy. 162 00:09:49,056 --> 00:09:51,256 If we want to survive in the universe, 163 00:09:51,258 --> 00:09:54,526 we need to know more about this monster black hole. 164 00:09:56,663 --> 00:10:00,932 The event horizon telescope is on a mission to do just that. 165 00:10:00,934 --> 00:10:04,169 Question is can it succeed? 166 00:10:09,042 --> 00:10:16,681 ♪ 167 00:10:16,683 --> 00:10:18,316 narrator: The center of the milky way 168 00:10:18,318 --> 00:10:21,186 is home to a supermassive black hole, 169 00:10:21,188 --> 00:10:24,389 sagittarius a-star. 170 00:10:24,391 --> 00:10:26,324 At least we think it is. 171 00:10:29,029 --> 00:10:30,962 We've never seen the supermassive 172 00:10:30,964 --> 00:10:32,597 black hole directly. 173 00:10:32,599 --> 00:10:36,201 But we have seen stars racing around the core. 174 00:10:37,738 --> 00:10:39,537 Filippenko: The speeds of the stars 175 00:10:39,539 --> 00:10:42,807 zipping around the center of our milky way galaxy 176 00:10:42,809 --> 00:10:45,377 indicate that there's something very massive 177 00:10:45,379 --> 00:10:47,445 and very compact there, 178 00:10:47,447 --> 00:10:51,950 indeed, 4 million times as massive as our sun 179 00:10:51,952 --> 00:10:55,954 in a volume smaller than that of our solar system. 180 00:10:55,956 --> 00:11:00,025 It's got to be a black hole basically. 181 00:11:00,027 --> 00:11:02,327 Narrator: By measuring the orbits of stars 182 00:11:02,329 --> 00:11:03,595 in our galaxy center... 183 00:11:07,534 --> 00:11:09,968 ...We estimate that sagittarius a-star 184 00:11:09,970 --> 00:11:12,804 is over a hundred times wider than our sun. 185 00:11:16,009 --> 00:11:19,911 But despite its size, the black hole is hidden. 186 00:11:22,015 --> 00:11:23,381 Tremblay: One of the immediate challenges 187 00:11:23,383 --> 00:11:24,949 of actually observing black holes 188 00:11:24,951 --> 00:11:29,154 is the fact that they don't emit light and so you can't see them. 189 00:11:29,156 --> 00:11:31,222 Right? So we've never actually seen a black hole. 190 00:11:31,224 --> 00:11:33,291 We've only seen the stuff around a black hole 191 00:11:33,293 --> 00:11:35,960 or we have seen the effects that that black hole 192 00:11:35,962 --> 00:11:38,329 imparts on its ambient surroundings. 193 00:11:40,434 --> 00:11:44,502 Narrator: That's where the event horizon telescope came in. 194 00:11:44,504 --> 00:11:49,808 Its goal was to photograph sagittarius a-star, 195 00:11:49,810 --> 00:11:53,445 not the black hole itself, but its shadow. 196 00:11:55,048 --> 00:11:57,882 Around it is this a gas that is moving around the black hole 197 00:11:57,884 --> 00:12:00,385 that's super heated to millions of degrees. 198 00:12:00,387 --> 00:12:01,720 And what the event horizon telescope 199 00:12:01,722 --> 00:12:04,389 is trying to see is the shadow of a black hole. 200 00:12:06,393 --> 00:12:09,994 Narrator: Light from the hot gas around sagittarius a-star 201 00:12:09,996 --> 00:12:12,197 frames the giant shadow. 202 00:12:12,199 --> 00:12:17,469 It could be up to 93 million miles across. 203 00:12:17,471 --> 00:12:21,806 Problem is sagittarius a-star is so far away 204 00:12:21,808 --> 00:12:27,278 that the supermassive black hole is still incredibly hard to see. 205 00:12:27,280 --> 00:12:29,347 Plait: Sagittarius a-star is big, 206 00:12:29,349 --> 00:12:32,250 but it's 26,000 light-years away. 207 00:12:32,252 --> 00:12:34,719 A single light-year is 6 trillion miles. 208 00:12:34,721 --> 00:12:36,821 So this is a long, long walk. 209 00:12:36,823 --> 00:12:38,690 And even though it's big, 210 00:12:38,692 --> 00:12:41,326 that distance shrinks its apparent size 211 00:12:41,328 --> 00:12:45,330 to just a tiny little dot on the sky. 212 00:12:45,332 --> 00:12:47,966 Narrator: To see the tiny dot, 213 00:12:47,968 --> 00:12:51,803 we need a telescope the size of the earth. 214 00:12:51,805 --> 00:12:52,904 How do you possibly do that? 215 00:12:52,906 --> 00:12:56,474 You can't build that telescope, right? 216 00:12:56,476 --> 00:12:57,575 Well, there's a trick. 217 00:12:57,577 --> 00:12:59,244 You actually get a few different telescopes 218 00:12:59,246 --> 00:13:02,413 and you spread them out over the surface of the earth. 219 00:13:02,415 --> 00:13:08,052 ♪ 220 00:13:08,054 --> 00:13:11,523 doeleman: And when we had all of these sites together, 221 00:13:11,525 --> 00:13:14,626 we wind up being able to take an image of something 222 00:13:14,628 --> 00:13:18,930 that is really, really impossibly small. 223 00:13:18,932 --> 00:13:22,300 Narrator: To gather enough light to see a target this small, 224 00:13:22,302 --> 00:13:25,103 the team take long-exposure images 225 00:13:25,105 --> 00:13:27,906 of sagittarius a-star's shadow... 226 00:13:31,711 --> 00:13:34,579 ...But there's a problem. 227 00:13:34,581 --> 00:13:37,382 The accretion disk moves too much for us 228 00:13:37,384 --> 00:13:39,384 to capture a clear image. 229 00:13:42,589 --> 00:13:44,689 When you're taking a long exposure of a person, 230 00:13:44,691 --> 00:13:46,157 right, you need them to be really, 231 00:13:46,159 --> 00:13:47,926 really still, right? 232 00:13:47,928 --> 00:13:49,494 Because if they're moving around a lot, 233 00:13:49,496 --> 00:13:51,362 they're going to blur the image out. 234 00:13:51,364 --> 00:13:52,831 And that kind of thing is happening 235 00:13:52,833 --> 00:13:54,833 when we observe sagittarius a-star 236 00:13:54,835 --> 00:13:57,235 because it is unwilling to sit still for us. 237 00:13:57,237 --> 00:13:58,937 It is booming and banging and flashing 238 00:13:58,939 --> 00:14:03,174 on the timescale of literally hours. 239 00:14:03,176 --> 00:14:06,311 Narrator: As glowing material orbits the black hole 240 00:14:06,313 --> 00:14:07,912 at 30% the speed of light, 241 00:14:07,914 --> 00:14:11,416 sagittarius a-star's shadow blurs. 242 00:14:13,820 --> 00:14:16,120 Future developments may allow us 243 00:14:16,122 --> 00:14:18,790 to see sagittarius a-star clearly. 244 00:14:21,561 --> 00:14:24,429 For now, we can't capture an accurate image 245 00:14:24,431 --> 00:14:27,265 of our galaxy's supermassive black hole. 246 00:14:30,070 --> 00:14:33,404 But the hunt to see a supermassive black hole 247 00:14:33,406 --> 00:14:34,839 wasn't over. 248 00:14:34,841 --> 00:14:38,676 The event horizon telescope turned to another galaxy 249 00:14:38,678 --> 00:14:43,548 54 million light-years away -- m87. 250 00:14:44,985 --> 00:14:48,086 M87 is an absolute beast of a galaxy. 251 00:14:48,088 --> 00:14:50,221 It's the so-called brightest cluster galaxy. 252 00:14:50,223 --> 00:14:52,991 These are among the largest galaxies in the universe. 253 00:14:55,028 --> 00:14:56,895 Narrator: And m87 is home 254 00:14:56,897 --> 00:14:59,764 to another supermassive black hole -- 255 00:14:59,766 --> 00:15:02,800 the giant m87 star. 256 00:15:04,237 --> 00:15:09,607 M87 star is so massive that the gravitational region 257 00:15:09,609 --> 00:15:12,176 that's interesting is actually easier to image 258 00:15:12,178 --> 00:15:14,579 than the black hole in our own galaxy. 259 00:15:17,651 --> 00:15:22,120 Narrator: M87 star is over a thousand times more massive 260 00:15:22,122 --> 00:15:24,188 than sagittarius a-star 261 00:15:24,190 --> 00:15:28,159 and has a far larger accretion disk. 262 00:15:28,161 --> 00:15:31,496 When photographing a black hole, size matters, 263 00:15:31,498 --> 00:15:36,034 because big accretion disks project more stable light, 264 00:15:36,036 --> 00:15:39,237 so images of them don't blur as much. 265 00:15:42,242 --> 00:15:44,575 In April of 2019, 266 00:15:44,577 --> 00:15:49,113 the event horizon team unveiled their image. 267 00:15:49,115 --> 00:15:52,717 We have seen what we thought was unseeable. 268 00:15:52,719 --> 00:15:57,388 We have seen and taken a picture of a black hole. 269 00:15:57,390 --> 00:15:58,656 [ applause ] 270 00:15:58,658 --> 00:16:05,229 ♪ 271 00:16:05,231 --> 00:16:06,631 I've been working on this project 272 00:16:06,633 --> 00:16:09,634 for almost six years now, and so, this is something 273 00:16:09,636 --> 00:16:13,972 we've been looking forward to for a really long time. 274 00:16:13,974 --> 00:16:16,607 Narrator: Capturing this image took decades of work 275 00:16:16,609 --> 00:16:20,478 by hundreds of scientists all over the world. 276 00:16:23,350 --> 00:16:25,783 Galison: I was really stunned. 277 00:16:25,785 --> 00:16:29,721 Suddenly, when you say that's the real thing, that's amazing. 278 00:16:29,723 --> 00:16:31,489 It really affected me. 279 00:16:31,491 --> 00:16:34,525 This is something 6 1/2 billion times 280 00:16:34,527 --> 00:16:36,194 the mass of the sun, 281 00:16:36,196 --> 00:16:41,599 55 million light-years away and we're looking at it. 282 00:16:41,601 --> 00:16:44,535 Tremblay: So when you look at the image, it's totally fine. 283 00:16:44,537 --> 00:16:46,070 You're totally forgiven for thinking, 284 00:16:46,072 --> 00:16:48,606 "ah, it looks a little blurry." 285 00:16:48,608 --> 00:16:52,076 but I cannot reiterate enough 286 00:16:52,078 --> 00:16:55,179 how profound this image actually is. 287 00:16:55,181 --> 00:16:59,283 We are seeing just a hair's width away from a discontinuity 288 00:16:59,285 --> 00:17:01,652 in the fabric of space-time itself. 289 00:17:01,654 --> 00:17:05,523 Actually seeing so close to an actual event horizon, 290 00:17:05,525 --> 00:17:07,959 a discontinuity in the fabric of space-time, 291 00:17:07,961 --> 00:17:11,396 never seemed possible. 292 00:17:11,398 --> 00:17:14,966 Narrator: This image of the heart of a distant galaxy 293 00:17:14,968 --> 00:17:19,570 helps us understand supermassive black holes like never before. 294 00:17:21,741 --> 00:17:24,342 Straughn: When we observe supermassive black holes 295 00:17:24,344 --> 00:17:26,711 in other galaxies, including the one in m87, 296 00:17:26,713 --> 00:17:28,946 we're able to learn more about the big picture 297 00:17:28,948 --> 00:17:32,683 of how these massive black holes form and evolve over time. 298 00:17:32,685 --> 00:17:34,419 And that in turn, helps us understand 299 00:17:34,421 --> 00:17:35,753 how our milky way galaxy 300 00:17:35,755 --> 00:17:38,256 and its super massive black hole has formed. 301 00:17:40,427 --> 00:17:42,794 Bouman: By studying, not just making images of black holes, 302 00:17:42,796 --> 00:17:44,695 but making videos of black holes, 303 00:17:44,697 --> 00:17:47,799 and seeing as that gas is spinning around it, 304 00:17:47,801 --> 00:17:50,902 we can try to map around a black hole more precisely 305 00:17:50,904 --> 00:17:52,870 and learn about its dynamics. 306 00:17:54,974 --> 00:17:57,375 Narrator: An image of sagittarius a-star 307 00:17:57,377 --> 00:17:58,776 remains out of reach, 308 00:17:58,778 --> 00:18:02,914 but in 2018, it shows a deadly side to its character. 309 00:18:04,684 --> 00:18:07,318 The supermassive black hole's accretion disk 310 00:18:07,320 --> 00:18:10,121 releases huge, powerful flares, 311 00:18:10,123 --> 00:18:13,791 and they could be pointed right at us. 312 00:18:22,001 --> 00:18:26,571 Narrator: In 2018, astronomers were studying a special star 313 00:18:26,573 --> 00:18:29,807 orbiting our galaxy's supermassive black hole. 314 00:18:29,809 --> 00:18:33,211 The star passes close to sagittarius a-star -- 315 00:18:33,213 --> 00:18:35,646 every 16 years. 316 00:18:35,648 --> 00:18:40,284 It's called s2, and by studying this star's fly-by, 317 00:18:40,286 --> 00:18:44,021 we hope to learn more about sagittarius a-star. 318 00:18:45,358 --> 00:18:48,226 Tremblay: We think that s2 may be the very closest star 319 00:18:48,228 --> 00:18:51,662 to the supermassive black hole in the center of our galaxy. 320 00:18:51,664 --> 00:18:53,764 At closest approach to sag a-star, 321 00:18:53,766 --> 00:18:58,369 s2 comes within 17 light hours or so of the surface. 322 00:19:00,907 --> 00:19:04,142 Narrator: The supermassive black hole's powerful gravity 323 00:19:04,144 --> 00:19:09,180 accelerates the star to 17 million miles an hour. 324 00:19:09,182 --> 00:19:12,517 That's fast enough to travel from new york to l.A. 325 00:19:12,519 --> 00:19:15,620 In half a second, 326 00:19:15,622 --> 00:19:19,357 but it's not the star's speed that excites scientists. 327 00:19:20,393 --> 00:19:23,194 This is a great star, because it's on an elliptical orbit 328 00:19:23,196 --> 00:19:25,763 that takes it fairly far from the black hole, 329 00:19:25,765 --> 00:19:27,064 but every few years, 330 00:19:27,066 --> 00:19:30,635 it passes right above the supermassive black hole. 331 00:19:32,705 --> 00:19:36,941 Narrator: As we tracked s2's swing around sagittarius a-star, 332 00:19:36,943 --> 00:19:40,511 we detected powerful bursts of infrared light 333 00:19:40,513 --> 00:19:44,182 coming from the direction of the supermassive black hole. 334 00:19:46,653 --> 00:19:48,319 Plait: There's a blob of gas 335 00:19:48,321 --> 00:19:51,022 that is orbiting very close to the black hole, 336 00:19:51,024 --> 00:19:53,558 and it was flaring as it went around. 337 00:19:53,560 --> 00:19:55,726 There were three separate flares of light 338 00:19:55,728 --> 00:19:59,063 that they were able to detect. 339 00:19:59,065 --> 00:20:00,965 Narrator: The flares didn't come directly 340 00:20:00,967 --> 00:20:04,435 from the supermassive black hole, 341 00:20:04,437 --> 00:20:07,672 they came from the material around it. 342 00:20:10,210 --> 00:20:12,777 The flares that were discovered are thought to originate 343 00:20:12,779 --> 00:20:14,278 from magnetic storms 344 00:20:14,280 --> 00:20:18,482 in this very, very hot turbulent gas around the black hole. 345 00:20:20,887 --> 00:20:23,254 Narrator: The extreme heat in the accretion disk 346 00:20:23,256 --> 00:20:26,390 strips electrons from atoms of gas. 347 00:20:26,392 --> 00:20:30,261 The stripped electrons and hot gas form a plasma, 348 00:20:30,263 --> 00:20:32,964 which creates powerful magnetic fields 349 00:20:32,966 --> 00:20:35,266 when accelerated to high speeds. 350 00:20:37,237 --> 00:20:39,503 Tremblay: Because some super massive black holes 351 00:20:39,505 --> 00:20:40,805 have these superheated, 352 00:20:40,807 --> 00:20:44,175 rapidly spinning vortices of gas swirling around them, 353 00:20:44,177 --> 00:20:46,210 you get these very, very powerful, 354 00:20:46,212 --> 00:20:48,546 very tightly wound magnetic fields. 355 00:20:50,617 --> 00:20:52,750 And there's energy stored in that magnetic field. 356 00:20:52,752 --> 00:20:55,686 It's like a bunch of piano wires all tangled up. 357 00:20:55,688 --> 00:20:58,589 And if these things interact with each other, they can snap, 358 00:20:58,591 --> 00:21:01,225 and when they snap, that energy is released. 359 00:21:05,431 --> 00:21:07,698 Tremblay: You'll get this enormous release of energy 360 00:21:07,700 --> 00:21:11,269 as these coils of magnetic fields effectively snap. 361 00:21:11,271 --> 00:21:15,906 And when they do so, just like on the surface of our sun, 362 00:21:15,908 --> 00:21:18,542 they release an enormous flare of gas. 363 00:21:22,148 --> 00:21:27,385 Narrator: These powerful flares can be millions of miles wide 364 00:21:27,387 --> 00:21:31,622 and come packed with superheated gas and plasma. 365 00:21:35,194 --> 00:21:37,995 Solar flares release as much energy 366 00:21:37,997 --> 00:21:40,698 as 10 million volcanic explosions. 367 00:21:40,700 --> 00:21:45,569 ♪ 368 00:21:45,571 --> 00:21:50,508 flares from sagittarius a-star's accretion disk 369 00:21:50,510 --> 00:21:55,579 are like millions of solar flares all going off at once. 370 00:21:58,318 --> 00:22:01,986 It's kind of like comparing a nuclear weapon to a firecracker. 371 00:22:04,123 --> 00:22:06,857 Narrator: Sagittarius a-star's flares 372 00:22:06,859 --> 00:22:09,527 release intense blasts of radiation, 373 00:22:09,529 --> 00:22:12,563 but by watching the flares from earth, 374 00:22:12,565 --> 00:22:14,532 we can learn about the orientation 375 00:22:14,534 --> 00:22:17,601 of the supermassive black hole's accretion disk. 376 00:22:19,372 --> 00:22:21,472 Tremblay: This gas that's in this accretion disk 377 00:22:21,474 --> 00:22:25,242 around the black hole is like a friendly helper 378 00:22:25,244 --> 00:22:27,378 shining a flashlight back toward earth. 379 00:22:27,380 --> 00:22:29,780 And we can watch the orbit of these flashlights 380 00:22:29,782 --> 00:22:32,116 and help understand the orientation of gas 381 00:22:32,118 --> 00:22:33,884 that swirls around the black hole. 382 00:22:37,457 --> 00:22:39,423 We think we're getting a bird's-eye view of it. 383 00:22:39,425 --> 00:22:41,092 And looking down the barrel, 384 00:22:41,094 --> 00:22:45,596 we're looking at the accretion disk basically face-on. 385 00:22:45,598 --> 00:22:48,132 That means that any material that gets blasted away 386 00:22:48,134 --> 00:22:50,968 from the black hole could be aimed right at us. 387 00:22:53,973 --> 00:22:57,475 Narrator: Should we be worried about the flares reaching earth? 388 00:22:59,078 --> 00:23:01,245 Plait: It sounds worrisome, this blob of gas 389 00:23:01,247 --> 00:23:03,481 emitting these huge flares of light, 390 00:23:03,483 --> 00:23:07,251 but you've got to realize, this is 26,000 light-years away. 391 00:23:07,253 --> 00:23:08,552 That is a long way. 392 00:23:08,554 --> 00:23:11,122 It took an extremely sensitive detector 393 00:23:11,124 --> 00:23:13,824 on one of the largest telescopes on earth 394 00:23:13,826 --> 00:23:16,727 to be able to see this at all. 395 00:23:16,729 --> 00:23:18,996 Narrator: Earth is safe for now, 396 00:23:18,998 --> 00:23:22,199 but the more we learn about the galaxy center, 397 00:23:22,201 --> 00:23:25,136 the more terrifying it becomes. 398 00:23:25,138 --> 00:23:27,238 We know of sagittarius a-star, 399 00:23:27,240 --> 00:23:29,206 the central supermassive black hole, 400 00:23:29,208 --> 00:23:31,008 but now we're beginning to suspect 401 00:23:31,010 --> 00:23:33,577 that it might not be alone. 402 00:23:35,214 --> 00:23:37,815 Narrator: A dangerous swarm of black holes 403 00:23:37,817 --> 00:23:41,719 could be racing around the center of the milky way. 404 00:23:41,721 --> 00:23:44,922 Thousands more may be hiding from sight. 405 00:23:47,960 --> 00:23:53,697 ♪ 406 00:23:53,699 --> 00:23:57,601 narrator: The supermassive black hole, sagittarius a-star, 407 00:23:57,603 --> 00:24:00,070 dominates the center of the milky way... 408 00:24:02,108 --> 00:24:04,041 ...Affecting star formation... 409 00:24:06,212 --> 00:24:09,380 ...And carving out vast gas bubbles in space. 410 00:24:11,751 --> 00:24:16,554 But sagittarius a-star might not be the only black hole in town, 411 00:24:16,556 --> 00:24:19,423 or even the most dangerous. 412 00:24:21,828 --> 00:24:23,027 Thaller: We've known for a long time 413 00:24:23,029 --> 00:24:24,462 that there's a supermassive black hole 414 00:24:24,464 --> 00:24:26,363 in the very heart of our galaxy, 415 00:24:26,365 --> 00:24:29,533 but there may be an angry swarm of smaller black holes, 416 00:24:29,535 --> 00:24:32,303 buzzing all around it. 417 00:24:32,305 --> 00:24:34,605 Narrator: In April of 2018, 418 00:24:34,607 --> 00:24:37,308 astronomers led by columbia university 419 00:24:37,310 --> 00:24:39,844 revealed the results of a hunting mission 420 00:24:39,846 --> 00:24:42,012 in the center of the galaxy. 421 00:24:42,014 --> 00:24:45,783 They'd used 12 years of chandra observatory data 422 00:24:45,785 --> 00:24:49,987 to seek out stellar mass black holes. 423 00:24:49,989 --> 00:24:52,590 Black holes that are made from the death of stars, 424 00:24:52,592 --> 00:24:54,225 from supernova explosions, 425 00:24:54,227 --> 00:24:56,927 are called stellar mass black holes. 426 00:24:56,929 --> 00:25:02,099 ♪ 427 00:25:02,101 --> 00:25:04,068 and these are made from stars 428 00:25:04,070 --> 00:25:06,871 that were many times the mass of the sun. 429 00:25:09,709 --> 00:25:14,345 Narrator: Finding stellar mass black holes is tough. 430 00:25:14,347 --> 00:25:17,381 Light can't escape a black hole's gravity, 431 00:25:17,383 --> 00:25:19,383 so we can't see them directly. 432 00:25:22,688 --> 00:25:26,924 And stellar mass black holes are only tens of miles wide, 433 00:25:26,926 --> 00:25:30,027 making them almost impossible to detect. 434 00:25:32,265 --> 00:25:34,698 So astronomers look for a special type 435 00:25:34,700 --> 00:25:36,667 of stellar mass black hole. 436 00:25:40,339 --> 00:25:44,275 One of the ways that we look for stellar mass black holes, 437 00:25:44,277 --> 00:25:50,047 is that they often are vampires eating a companion star. 438 00:25:53,786 --> 00:25:58,188 Narrator: These vampires are part of a binary pair, 439 00:25:58,190 --> 00:26:02,560 a stellar mass black hole in orbit with a living star, 440 00:26:02,562 --> 00:26:05,930 the black hole feasting on its partner. 441 00:26:07,366 --> 00:26:08,732 Tremblay: That black hole 442 00:26:08,734 --> 00:26:11,468 is like a very, very deadly parasite for that star. 443 00:26:11,470 --> 00:26:14,271 It is ripping mass off the surface of that star, 444 00:26:14,273 --> 00:26:17,641 and that matter is raining down toward the black hole itself. 445 00:26:20,980 --> 00:26:23,047 Sutter: And that material lights up, 446 00:26:23,049 --> 00:26:25,616 so this allows us to hunt for black holes, 447 00:26:25,618 --> 00:26:28,686 not through taking pictures of black holes directly, 448 00:26:28,688 --> 00:26:32,990 but through seeing the material falling to its doom. 449 00:26:32,992 --> 00:26:35,059 Narrator: The problem is, 450 00:26:35,061 --> 00:26:37,394 gas and dust spread throughout the galaxy 451 00:26:37,396 --> 00:26:41,599 stops visible light from the binary pair reaching earth. 452 00:26:41,601 --> 00:26:44,702 But the binary pair release another type of light 453 00:26:44,704 --> 00:26:48,806 that passes through the gas and dust more easily -- 454 00:26:48,808 --> 00:26:50,741 x-rays. 455 00:26:50,743 --> 00:26:53,277 Mingarelli: The system itself is emitting x-rays, 456 00:26:53,279 --> 00:26:55,279 so they're called x-ray binaries. 457 00:26:55,281 --> 00:26:57,948 So these are useful, because the x-ray emission 458 00:26:57,950 --> 00:26:59,450 can be very powerful 459 00:26:59,452 --> 00:27:02,152 and can be potentially seen from the earth, 460 00:27:02,154 --> 00:27:04,221 even though the binary is very far away, 461 00:27:04,223 --> 00:27:06,023 say, at the galactic center. 462 00:27:08,628 --> 00:27:12,396 Narrator: The glowing disks of material in x-ray binary systems 463 00:27:12,398 --> 00:27:16,000 are almost a million times smaller than the accretion disk 464 00:27:16,002 --> 00:27:19,336 surrounding sagittarius a-star, too small 465 00:27:19,338 --> 00:27:23,540 for us to see the material swirling around them in detail. 466 00:27:25,044 --> 00:27:30,447 So, we see the x-ray binaries as pinpricks of x-ray light. 467 00:27:33,185 --> 00:27:36,787 Astronomers detect 12 of these x-ray binaries 468 00:27:36,789 --> 00:27:40,357 in a small 3-light-year-wide patch of space 469 00:27:40,359 --> 00:27:42,192 at the galactic center. 470 00:27:42,194 --> 00:27:44,762 And that means that there could be a much larger collection 471 00:27:44,764 --> 00:27:47,765 of these relatively tiny stellar mass black holes 472 00:27:47,767 --> 00:27:51,268 in the heart of our galaxy. 473 00:27:51,270 --> 00:27:53,671 If black holes form the way we think they do, 474 00:27:53,673 --> 00:27:56,440 there very likely may be swarms of black holes 475 00:27:56,442 --> 00:27:58,542 racing around sagittarius a-star. 476 00:28:01,480 --> 00:28:04,448 Narrator: But x-ray binaries that are powerful enough for us 477 00:28:04,450 --> 00:28:08,852 to detect are incredibly rare. 478 00:28:08,854 --> 00:28:13,590 So we estimate that for the dozen x-ray binaries discovered, 479 00:28:13,592 --> 00:28:15,526 there could be up to a thousand more. 480 00:28:15,528 --> 00:28:20,798 ♪ 481 00:28:20,800 --> 00:28:25,536 in total, there could be 20,000 stellar mass black holes 482 00:28:25,538 --> 00:28:28,672 in this 3-light-year region of space. 483 00:28:28,674 --> 00:28:38,048 ♪ 484 00:28:38,050 --> 00:28:41,852 why are these black holes swarming in the galaxy center? 485 00:28:41,854 --> 00:28:45,789 It appears they've migrated from the rest of the milky way. 486 00:28:47,326 --> 00:28:49,359 Tremblay: Through a process called dynamical friction, 487 00:28:49,361 --> 00:28:51,862 black holes can actually sink to the centers of galaxies 488 00:28:51,864 --> 00:28:55,933 very, very rapidly, like dropping a stone into a pond. 489 00:28:55,935 --> 00:28:58,101 What that means is that an errant, 490 00:28:58,103 --> 00:29:00,003 wandering black hole might eventually 491 00:29:00,005 --> 00:29:02,606 find its way toward the center of our own galaxy, 492 00:29:02,608 --> 00:29:06,577 where sagittarius a-star resides. 493 00:29:06,579 --> 00:29:10,614 Narrator: As stellar mass black holes orbit the galaxy, 494 00:29:10,616 --> 00:29:12,683 they interact gravitationally 495 00:29:12,685 --> 00:29:15,586 with stars and clouds of gas and dust. 496 00:29:17,389 --> 00:29:20,524 These interactions push the black holes 497 00:29:20,526 --> 00:29:23,827 towards the center of the galaxy, 498 00:29:23,829 --> 00:29:25,429 where the black holes swarm. 499 00:29:25,431 --> 00:29:30,367 ♪ 500 00:29:30,369 --> 00:29:34,471 a swarm of stellar mass black holes sounds deadly, 501 00:29:34,473 --> 00:29:37,007 but it may not be the most lethal thing 502 00:29:37,009 --> 00:29:38,842 in the center of the milky way. 503 00:29:41,313 --> 00:29:45,382 A surprising observation indicates that there is a lot 504 00:29:45,384 --> 00:29:49,386 of antimatter in the center of our galaxy. 505 00:29:49,388 --> 00:29:52,523 Narrator: And when antimatter meets matter, 506 00:29:52,525 --> 00:29:55,225 the results are explosive. 507 00:29:58,898 --> 00:30:05,602 ♪ 508 00:30:05,604 --> 00:30:07,437 narrator: In 2017, 509 00:30:07,439 --> 00:30:11,875 astronomers tried to solve a decades-old cosmic mystery... 510 00:30:14,814 --> 00:30:17,748 ...Unexplained high-energy radiation 511 00:30:17,750 --> 00:30:19,683 streaming through our galaxy. 512 00:30:23,422 --> 00:30:25,923 At first, we didn't know where it was from. 513 00:30:28,427 --> 00:30:31,228 But we discovered it was gamma radiation 514 00:30:31,230 --> 00:30:34,932 coming from somewhere in the center of the milky way. 515 00:30:37,536 --> 00:30:40,237 The question is, what's making these gamma rays? 516 00:30:40,239 --> 00:30:41,972 That's hard to do. 517 00:30:41,974 --> 00:30:43,507 It's not like you can rub your hands together 518 00:30:43,509 --> 00:30:46,910 and generate gamma rays. 519 00:30:46,912 --> 00:30:48,979 Narrator: When we took a closer look at the gamma rays, 520 00:30:48,981 --> 00:30:52,783 we discovered the signature of the most explosive substance 521 00:30:52,785 --> 00:30:55,419 in the universe -- antimatter. 522 00:30:59,258 --> 00:31:02,559 Antimatter is like normal matter 523 00:31:02,561 --> 00:31:04,561 but with opposite charge. 524 00:31:04,563 --> 00:31:07,030 That's it. It's matter's evil twin. 525 00:31:09,134 --> 00:31:11,935 Narrator: When evil twin meets good twin, 526 00:31:11,937 --> 00:31:14,404 it is not a happy reunion. 527 00:31:17,309 --> 00:31:18,742 Plait: Antimatter is scary. 528 00:31:18,744 --> 00:31:21,445 It's not like you want to have some in your kitchen. 529 00:31:21,447 --> 00:31:23,647 This stuff is very, very explosive, 530 00:31:23,649 --> 00:31:25,749 if you want to think of it that way. 531 00:31:25,751 --> 00:31:27,484 If it touches normal matter, 532 00:31:27,486 --> 00:31:29,786 it releases a huge amount of energy. 533 00:31:31,724 --> 00:31:33,757 Narrator: When matter and antimatter combine, 534 00:31:33,759 --> 00:31:36,159 they annihilate each other and transform 535 00:31:36,161 --> 00:31:39,663 into high-energy radiation, just like the gamma rays 536 00:31:39,665 --> 00:31:42,766 seen streaming out of the center of the milky way. 537 00:31:44,603 --> 00:31:47,537 We see antimatter throughout the galaxy, 538 00:31:47,539 --> 00:31:49,973 but strangely, the galactic center 539 00:31:49,975 --> 00:31:54,511 seemed to have 40% more antimatter than anywhere else. 540 00:31:56,815 --> 00:31:58,649 Right now in the heart of our galaxy, 541 00:31:58,651 --> 00:32:01,685 we actually observe fountains of antimatter 542 00:32:01,687 --> 00:32:04,655 that are producing 10 trillion tons 543 00:32:04,657 --> 00:32:07,824 of antimatter every second. 544 00:32:07,826 --> 00:32:09,526 One of the big questions that we've wondered about 545 00:32:09,528 --> 00:32:12,429 for a very long time, is what's the origin of this stuff? 546 00:32:15,801 --> 00:32:19,403 Narrator: Initially, there were several suspects. 547 00:32:19,405 --> 00:32:21,171 Plait: One possible source of antimatter 548 00:32:21,173 --> 00:32:24,808 is the central black hole, sagittarius a-star. 549 00:32:24,810 --> 00:32:26,443 Matter can be swirling around this 550 00:32:26,445 --> 00:32:28,178 and it can have such high energy 551 00:32:28,180 --> 00:32:29,947 that it can create antimatter. 552 00:32:33,218 --> 00:32:34,918 Narrator: But the antimatter 553 00:32:34,920 --> 00:32:37,054 isn't coming from a single point, 554 00:32:37,056 --> 00:32:41,558 it's spread across thousands of light-years of space. 555 00:32:41,560 --> 00:32:43,226 So sagittarius a-star 556 00:32:43,228 --> 00:32:46,730 can't be the source of the gamma-ray stream. 557 00:32:49,668 --> 00:32:52,569 Another suspect was dark matter. 558 00:32:55,040 --> 00:32:56,573 One of the biggest mysteries in the universe 559 00:32:56,575 --> 00:32:58,642 right now is dark matter. 560 00:32:58,644 --> 00:33:01,511 We know that the majority of mass in the universe 561 00:33:01,513 --> 00:33:03,146 is not in the same form that we are. 562 00:33:03,148 --> 00:33:04,915 It's not made of atoms, 563 00:33:04,917 --> 00:33:07,451 but whatever sort of particle it is or may be, 564 00:33:07,453 --> 00:33:10,854 if these things collide, they can produce antimatter, 565 00:33:10,856 --> 00:33:12,589 and that will produce the gamma rays. 566 00:33:12,591 --> 00:33:15,225 So it's possible that as we look into the heart of the galaxy 567 00:33:15,227 --> 00:33:17,027 and see these extra gamma rays, 568 00:33:17,029 --> 00:33:19,629 that's the signal that dark matter is there. 569 00:33:23,669 --> 00:33:26,737 Narrator: But the gamma ray stream we detected is too weak 570 00:33:26,739 --> 00:33:29,139 to have been created by dark matter. 571 00:33:31,810 --> 00:33:35,679 Then we had a breakthrough. 572 00:33:35,681 --> 00:33:40,317 We discovered that a special metal called titanium-44 573 00:33:40,319 --> 00:33:43,487 could be responsible for the gamma-ray stream. 574 00:33:47,326 --> 00:33:50,527 Titanium-44 is a highly radioactive element. 575 00:33:50,529 --> 00:33:52,229 That means that it wants to decay 576 00:33:52,231 --> 00:33:54,064 into other types of nuclei. 577 00:33:57,069 --> 00:33:59,636 Narrator: When titanium-44 decays, 578 00:33:59,638 --> 00:34:01,438 it gives off antimatter. 579 00:34:01,440 --> 00:34:05,675 But to produce the antimatter seen in the galaxy's core, 580 00:34:05,677 --> 00:34:09,112 you would need a lot of titanium-44. 581 00:34:09,114 --> 00:34:14,217 It could be created in rare energetic events, 582 00:34:14,219 --> 00:34:18,655 in the collision of two dead stars -- white dwarfs. 583 00:34:20,559 --> 00:34:23,393 A white dwarf star is a star that didn't have enough mass 584 00:34:23,395 --> 00:34:25,996 when it died to actually become a supernova. 585 00:34:25,998 --> 00:34:28,665 It just sort of cools off as a dead little cinder. 586 00:34:28,667 --> 00:34:30,333 But what if you have two white dwarfs 587 00:34:30,335 --> 00:34:32,135 that are orbiting around each other, 588 00:34:32,137 --> 00:34:34,938 and as they come closer and closer and collide, 589 00:34:34,940 --> 00:34:36,907 all of a sudden now, you have enough mass 590 00:34:36,909 --> 00:34:39,276 to actually kick a supernova explosion off. 591 00:34:39,278 --> 00:34:44,347 ♪ 592 00:34:44,349 --> 00:34:46,183 these particular kinds of supernovae 593 00:34:46,185 --> 00:34:49,052 are very good at producing titanium-44. 594 00:34:50,856 --> 00:34:53,657 So these kinds of supernovas are very, very good 595 00:34:53,659 --> 00:34:55,292 at making antimatter. 596 00:34:57,863 --> 00:35:00,864 Narrator: These supernovas erupt in the core of the galaxy 597 00:35:00,866 --> 00:35:03,200 once every 2,000 years. 598 00:35:06,205 --> 00:35:09,139 But outside of the core in the disk of the galaxy 599 00:35:09,141 --> 00:35:11,374 where our solar system orbits... 600 00:35:13,512 --> 00:35:16,746 ...These supernovas happen three times as often. 601 00:35:18,317 --> 00:35:22,152 So the gamma ray observations were wrong. 602 00:35:22,154 --> 00:35:25,856 There isn't more antimatter in the heart of the galaxy. 603 00:35:25,858 --> 00:35:28,091 It's our region of the galaxy 604 00:35:28,093 --> 00:35:31,194 that contains the most antimatter. 605 00:35:33,365 --> 00:35:36,133 Question is, are we in danger? 606 00:35:38,570 --> 00:35:39,769 Plait: If you take an ounce of matter 607 00:35:39,771 --> 00:35:41,738 and an ounce of antimatter and collide them, 608 00:35:41,740 --> 00:35:45,175 you're generating a megaton of energy, 609 00:35:45,177 --> 00:35:49,779 the equivalent of a million tons of tnt exploding. 610 00:35:49,781 --> 00:35:51,748 So you don't need much antimatter to generate 611 00:35:51,750 --> 00:35:54,684 a vast amount of energy. 612 00:35:54,686 --> 00:35:56,887 But the thing you have to remember is we live 613 00:35:56,889 --> 00:35:59,156 in this wonderful, dramatic environment 614 00:35:59,158 --> 00:36:00,357 of a larger universe. 615 00:36:00,359 --> 00:36:01,725 It's not dangerous. 616 00:36:01,727 --> 00:36:04,761 It's very far away from us, and it's fascinating. 617 00:36:07,232 --> 00:36:10,567 But all of this antimatter is being produced in our galaxy, 618 00:36:10,569 --> 00:36:13,603 so just sit back and enjoy the fireworks. 619 00:36:15,874 --> 00:36:18,375 Narrator: The center of the milky way 620 00:36:18,377 --> 00:36:19,876 is violent and extreme, 621 00:36:19,878 --> 00:36:22,812 but things could get a whole lot worse. 622 00:36:24,683 --> 00:36:26,850 Rogue supermassive black holes 623 00:36:26,852 --> 00:36:30,053 could be lurking near our galaxy, 624 00:36:30,055 --> 00:36:34,024 and they have the power to end life as we know it. 625 00:36:38,564 --> 00:36:45,202 ♪ 626 00:36:45,204 --> 00:36:49,439 narrator: The milky way is around 100,000 light-years across, 627 00:36:49,441 --> 00:36:54,511 and it's home to at least 200 billion stars, 628 00:36:54,513 --> 00:36:58,048 but it hasn't always been this large. 629 00:36:58,050 --> 00:37:01,418 We know that our milky way galaxy grew to the size 630 00:37:01,420 --> 00:37:06,756 it is now, which is huge, by eating other galaxies. 631 00:37:06,758 --> 00:37:09,059 And some of these galaxies would've had 632 00:37:09,061 --> 00:37:11,561 supermassive black holes in their centers. 633 00:37:14,199 --> 00:37:16,866 Narrator: When the milky way's gravity 634 00:37:16,868 --> 00:37:18,668 pulled in smaller galaxies, 635 00:37:18,670 --> 00:37:23,807 most of their material merged with the milky way, 636 00:37:23,809 --> 00:37:25,976 but some material like stars, 637 00:37:25,978 --> 00:37:29,446 could've been slung tens of thousands of light-years 638 00:37:29,448 --> 00:37:31,081 out of the milky way. 639 00:37:33,385 --> 00:37:36,886 This could've happened to a smaller galaxy's 640 00:37:36,888 --> 00:37:39,789 super massive black hole. 641 00:37:39,791 --> 00:37:41,458 Plait: It is entirely possible 642 00:37:41,460 --> 00:37:43,526 there are supermassive black holes 643 00:37:43,528 --> 00:37:46,963 wandering around out there, not in the center. 644 00:37:49,401 --> 00:37:51,201 Thaller: So how could it be possible that there's actually 645 00:37:51,203 --> 00:37:53,970 a supermassive black hole close to us wandering around, 646 00:37:53,972 --> 00:37:55,739 but we never even see it? 647 00:37:55,741 --> 00:37:59,209 Well, remember black hole means it's really, really black. 648 00:37:59,211 --> 00:38:02,045 It actually absorbs radiation and any energy. 649 00:38:02,047 --> 00:38:04,481 So unless something is falling into a black hole 650 00:38:04,483 --> 00:38:08,385 or orbiting around it, you're not going to see it. 651 00:38:08,387 --> 00:38:09,953 Tremblay: And so, if this supermassive black hole 652 00:38:09,955 --> 00:38:13,256 were hypothetically wandering the outskirts of our galaxy, 653 00:38:13,258 --> 00:38:15,225 well, there's a lot less gas there 654 00:38:15,227 --> 00:38:16,926 for that black hole to run into. 655 00:38:16,928 --> 00:38:18,128 And if there's no gas around 656 00:38:18,130 --> 00:38:20,530 that black hole, we will not see it. 657 00:38:22,668 --> 00:38:26,102 Narrator: The rogue supermassive black hole may not stay 658 00:38:26,104 --> 00:38:29,005 in the outskirts of the galaxy forever. 659 00:38:29,007 --> 00:38:32,642 Gravitational interactions slowly pull it back 660 00:38:32,644 --> 00:38:34,644 into the milky way. 661 00:38:34,646 --> 00:38:36,446 Billions of years later, 662 00:38:36,448 --> 00:38:41,217 the supermassive black hole could arrive in the center. 663 00:38:45,557 --> 00:38:48,692 When this rogue supermassive black hole meets up with 664 00:38:48,694 --> 00:38:53,530 sagittarius a-star, the fuse is lit. 665 00:38:55,167 --> 00:38:57,634 The pair spiral towards each other... 666 00:39:00,906 --> 00:39:02,872 ...Spinning faster and faster, 667 00:39:02,874 --> 00:39:05,442 reaching up to half the speed of light. 668 00:39:05,444 --> 00:39:10,680 ♪ 669 00:39:10,682 --> 00:39:14,517 finally, the two black holes merge. 670 00:39:14,519 --> 00:39:20,790 ♪ 671 00:39:20,792 --> 00:39:21,991 tremblay: You would have 672 00:39:21,993 --> 00:39:24,160 an enormously energetic event on your hands. 673 00:39:24,162 --> 00:39:26,663 Those supermassive black holes could, in principle, 674 00:39:26,665 --> 00:39:30,533 merge together, create a huge blast of gravitational waves, 675 00:39:30,535 --> 00:39:34,371 accompanied by a profoundly energetic flash of light 676 00:39:34,373 --> 00:39:37,040 that could, in principle, endanger all life on earth. 677 00:39:37,042 --> 00:39:43,146 ♪ 678 00:39:43,148 --> 00:39:45,648 plait: It's literally a stretching 679 00:39:45,650 --> 00:39:47,817 and contracting of space itself. 680 00:39:47,819 --> 00:39:50,053 It's like grabbing the framework of space 681 00:39:50,055 --> 00:39:51,921 and it's shaking it really hard. 682 00:39:51,923 --> 00:39:53,890 And if this happens in our galaxy, 683 00:39:53,892 --> 00:39:59,028 the amount of energy emitted, that would be bad. 684 00:40:01,099 --> 00:40:03,299 Narrator: When the black holes collide, 685 00:40:03,301 --> 00:40:04,634 they release more energy 686 00:40:04,636 --> 00:40:08,671 than all the stars in the galaxy combined. 687 00:40:08,673 --> 00:40:15,478 ♪ 688 00:40:15,480 --> 00:40:17,847 plait: Should we be panicked about this? 689 00:40:17,849 --> 00:40:19,249 And the answer is no. 690 00:40:19,251 --> 00:40:21,184 The earth has been orbiting the sun 691 00:40:21,186 --> 00:40:23,887 for 4 1/2 billion years without any incident, right? 692 00:40:23,889 --> 00:40:26,523 We're pretty safe from them. 693 00:40:26,525 --> 00:40:30,660 Narrator: If we were around to see the two black holes collide, 694 00:40:30,662 --> 00:40:33,396 we'd witness the most destructive light show 695 00:40:33,398 --> 00:40:35,331 in the history of the galaxy. 696 00:40:38,003 --> 00:40:43,339 But for now, the center of our galaxy is relatively quiet, 697 00:40:43,341 --> 00:40:46,376 but it's still a terrible place to be. 698 00:40:49,915 --> 00:40:53,049 The center of our milky way is not a friendly place. 699 00:40:53,051 --> 00:40:56,820 It's nowhere you want to be. It's a bad neighborhood. 700 00:40:56,822 --> 00:41:00,924 You've got tons of stars, tons of radiation, 701 00:41:00,926 --> 00:41:05,028 and stars are being born and dying and exploding. 702 00:41:05,030 --> 00:41:06,896 You've got the central supermassive black hole. 703 00:41:06,898 --> 00:41:09,566 You've got a potential swarm of black holes. 704 00:41:09,568 --> 00:41:12,001 You've got accretion disks. You've got flares. 705 00:41:12,003 --> 00:41:16,105 You've got magnetic outbursts. You've got jets. 706 00:41:16,107 --> 00:41:18,675 Let's just stay out here in the suburbs, all right? 707 00:41:20,812 --> 00:41:22,145 Narrator: The center of our galaxy 708 00:41:22,147 --> 00:41:25,815 is one of the most nightmarish places in the cosmos. 709 00:41:28,620 --> 00:41:32,021 It's also home to some of the most incredible forces 710 00:41:32,023 --> 00:41:33,723 the universe has to offer. 711 00:41:36,528 --> 00:41:39,195 Whatever the future holds for our galaxy... 712 00:41:41,600 --> 00:41:46,870 ...The core of the milky way will be at the center of it all. 713 00:41:46,872 --> 00:41:50,406 Our home galaxy, the milky way, is our safe harbor, 714 00:41:50,408 --> 00:41:53,776 our island in this vast, cosmic ocean. 715 00:41:53,778 --> 00:41:56,779 And so to understand the heart of our galaxy, 716 00:41:56,781 --> 00:42:00,517 is to understand our home in this cosmic void.