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These are the user uploaded subtitles that are being translated: 1 00:00:04,490 --> 00:00:08,660 The fate of our galaxy hangs in the balance. 2 00:00:08,660 --> 00:00:14,900 The Milky Way is dying, and we don't know why. 3 00:00:14,900 --> 00:00:19,800 Our galaxy, like all galaxies, has a limited life-span. 4 00:00:19,800 --> 00:00:23,640 After that, it's lights out. 5 00:00:23,640 --> 00:00:26,510 The race is on to find a smoking gun. 6 00:00:28,850 --> 00:00:32,610 It's safe to say right now there are many ways to kill a galaxy. 7 00:00:35,820 --> 00:00:39,750 It's a cosmic crime scene investigation. 8 00:00:39,760 --> 00:00:42,920 Is it murder most foul? 9 00:00:42,930 --> 00:00:45,030 Or is it death by natural causes? 10 00:00:47,330 --> 00:00:49,800 The suspects are lined up. 11 00:00:49,800 --> 00:00:52,270 The interrogation is underway. 12 00:00:56,270 --> 00:00:58,570 It's another example of this big universe of ours 13 00:00:58,580 --> 00:01:01,110 throwing puzzles at us that now we have to solve. 14 00:01:04,050 --> 00:01:07,280 What is killing the Milky Way? 15 00:01:07,280 --> 00:01:10,290 Captions by vitac... www.vitac.com 16 00:01:10,290 --> 00:01:13,290 captions paid for by discovery communications 17 00:01:25,540 --> 00:01:27,870 Earth. 18 00:01:27,870 --> 00:01:30,440 Our home. 19 00:01:30,440 --> 00:01:34,640 Just one of 100 billion planets 20 00:01:34,640 --> 00:01:38,910 orbiting 400 billion stars 21 00:01:38,920 --> 00:01:42,580 that make up an immense galactic spiral... 22 00:01:44,590 --> 00:01:47,120 the Milky Way. 23 00:01:49,890 --> 00:01:52,490 Galaxies are where stars form, 24 00:01:52,500 --> 00:01:54,830 and, of course, planets form around stars, 25 00:01:54,830 --> 00:01:56,660 so the story of the Earth, 26 00:01:56,670 --> 00:01:58,900 of yourself, of the solar system 27 00:01:58,900 --> 00:02:02,340 has everything to do with the story of the galaxies. 28 00:02:05,640 --> 00:02:10,880 The story of the Milky Way begins 13.6 billion years ago, 29 00:02:10,880 --> 00:02:13,480 just after the big bang. 30 00:02:13,480 --> 00:02:17,550 It's a time when there are no planets and no stars... 31 00:02:17,550 --> 00:02:22,760 Just a vast, lumpy soup of superheated hydrogen gas. 32 00:02:25,500 --> 00:02:28,660 Over millions of years, the temperature drops, 33 00:02:28,670 --> 00:02:33,070 and gravity compresses the lumps down, until eventually 34 00:02:33,070 --> 00:02:37,870 the hydrogen molecules fuse and ignite a star. 35 00:02:42,350 --> 00:02:47,850 In time, billions of stars burst into life. 36 00:02:47,850 --> 00:02:51,120 And the Milky Way begins to take shape. 37 00:02:56,190 --> 00:02:58,930 You can think of a galaxy as sort of like a human being. 38 00:02:58,930 --> 00:03:01,360 When you're young and in your adolescent stage, 39 00:03:01,360 --> 00:03:02,830 you're vibrant and active. 40 00:03:02,830 --> 00:03:05,600 That's a young galaxy forming stars in a crazy way, 41 00:03:05,600 --> 00:03:07,240 and it's not even fully formed yet. 42 00:03:07,240 --> 00:03:09,900 At a certain point, galaxy reaches middle age, 43 00:03:09,910 --> 00:03:12,510 and a middle-aged galaxy really is what it's going to be... 44 00:03:12,510 --> 00:03:13,810 It has its shape... 45 00:03:13,810 --> 00:03:17,080 But in the long run, a galaxy will stop forming stars, 46 00:03:17,080 --> 00:03:20,720 and eventually, just like we all die, our galaxy will die. 47 00:03:24,020 --> 00:03:27,820 So, at what stage of life is the Milky Way? 48 00:03:27,820 --> 00:03:30,430 Is it a healthy, active youngster, 49 00:03:30,430 --> 00:03:32,590 or is it heading for its deathbed? 50 00:03:35,800 --> 00:03:39,530 Scientists can determine each galaxy's stage of life 51 00:03:39,540 --> 00:03:42,400 by its color. 52 00:03:42,410 --> 00:03:47,240 So, we see different colors of galaxies in the universe. 53 00:03:47,240 --> 00:03:49,780 We see galaxies that are tinted blue 54 00:03:49,780 --> 00:03:54,520 and galaxies that are tinted red. 55 00:03:54,520 --> 00:03:59,720 When we see a blue galaxy, that tends to be a younger galaxy 56 00:03:59,720 --> 00:04:04,030 full of bright, hot, newly formed stars. 57 00:04:06,500 --> 00:04:08,660 When we see a redder galaxy, 58 00:04:08,670 --> 00:04:11,830 that tends to be a dimmer, older galaxy 59 00:04:11,840 --> 00:04:15,670 that isn't forming new stars in the present moment. 60 00:04:15,670 --> 00:04:18,870 All its stars are aged and older and redder, 61 00:04:18,880 --> 00:04:22,510 and so the entire galaxy casts a different hue. 62 00:04:27,880 --> 00:04:32,820 So, what color is our galaxy? 63 00:04:32,820 --> 00:04:38,790 It's a simple question, but the answer is hard to come by, 64 00:04:38,800 --> 00:04:41,730 even though we've been looking at the Milky Way 65 00:04:41,730 --> 00:04:44,800 for thousands of years. 66 00:04:44,800 --> 00:04:46,870 The term "Milky Way" is ancient. 67 00:04:46,870 --> 00:04:49,070 It goes back to a time when in the dark sky, 68 00:04:49,070 --> 00:04:51,310 people noticed there was this light band 69 00:04:51,310 --> 00:04:53,640 that actually went from horizon to horizon, 70 00:04:53,640 --> 00:04:54,880 and that band turned out 71 00:04:54,880 --> 00:04:57,110 to be made of thousands and thousands of stars 72 00:04:57,110 --> 00:04:59,810 actually too far away to see individually. 73 00:04:59,820 --> 00:05:01,620 But it took us a long time to realize 74 00:05:01,620 --> 00:05:06,550 what the shape and the scale of the Milky Way galaxy is. 75 00:05:06,560 --> 00:05:09,420 The amazing thing to think about is that we actually don't know 76 00:05:09,430 --> 00:05:11,730 our home galaxy very well at all. 77 00:05:11,730 --> 00:05:15,430 We actually live in the middle of this disk of gas and dust, 78 00:05:15,430 --> 00:05:19,430 and that obscures our view of the larger Milky Way. 79 00:05:19,440 --> 00:05:22,000 Using visible light, we can't even see to the center, 80 00:05:22,010 --> 00:05:26,170 let alone the other side of the Milky Way galaxy. 81 00:05:30,180 --> 00:05:32,780 The solution is to use a form of light 82 00:05:32,780 --> 00:05:36,750 that passes through the gas and dust... 83 00:05:36,750 --> 00:05:38,320 Infrared. 84 00:05:41,830 --> 00:05:45,690 This is the Sloan digital sky survey telescope 85 00:05:45,700 --> 00:05:50,130 at the Apache point observatory in new Mexico. 86 00:05:50,130 --> 00:05:53,430 It's mapping the galaxy using infrared 87 00:05:53,440 --> 00:05:57,210 and giving scientists unprecedented insights. 88 00:05:59,810 --> 00:06:03,010 The first sensitive infrared observations really weren't done 89 00:06:03,010 --> 00:06:04,980 till the last 15 years, 90 00:06:04,980 --> 00:06:07,280 and each of these new windows on the universe 91 00:06:07,280 --> 00:06:09,080 teach us different things. 92 00:06:14,160 --> 00:06:15,720 In the last 15 years, 93 00:06:15,730 --> 00:06:21,060 Sloan has surveyed more than 250 million stars, 94 00:06:21,060 --> 00:06:26,330 analyzing their light to work out the color of the Milky Way. 95 00:06:26,340 --> 00:06:30,540 And what scientists saw shocked them. 96 00:06:30,540 --> 00:06:32,770 Until very recently, we thought the Milky Way 97 00:06:32,780 --> 00:06:34,780 was a young, healthy galaxy, 98 00:06:34,780 --> 00:06:36,240 but now there's evidence 99 00:06:36,250 --> 00:06:39,680 that we may be entering the pathway to death. 100 00:06:41,990 --> 00:06:46,520 The Sloan telescope reveals that star production in our galaxy 101 00:06:46,520 --> 00:06:49,520 is falling through the floor. 102 00:06:49,530 --> 00:06:52,490 The Milky Way is dying. 103 00:06:52,500 --> 00:06:56,160 And when it stops forming new stars, 104 00:06:56,170 --> 00:06:57,730 its time will be up. 105 00:07:00,200 --> 00:07:02,770 Paradoxically, our galaxy still has 106 00:07:02,770 --> 00:07:08,710 star-forming gas in the tank, so it should be healthy, 107 00:07:08,710 --> 00:07:11,210 but something is killing it off. 108 00:07:15,350 --> 00:07:18,050 So, the Milky Way galaxy is this wonderful disk 109 00:07:18,050 --> 00:07:21,920 filled with rich hydrogen gas, lots of dense dust clouds. 110 00:07:21,930 --> 00:07:24,530 It has everything you need there for star formation, 111 00:07:24,530 --> 00:07:27,860 but it seems to be slowing down and even turning off, 112 00:07:27,860 --> 00:07:31,530 and right now, we don't really understand what the culprit is. 113 00:07:36,170 --> 00:07:38,070 With a galaxy killer at large, 114 00:07:38,070 --> 00:07:42,280 scientists embark upon the biggest murder investigation 115 00:07:42,280 --> 00:07:44,450 in the history of the universe. 116 00:07:46,420 --> 00:07:48,520 Everything in science, when you're exploring a problem, 117 00:07:48,520 --> 00:07:50,820 is a bit like a crime scene. 118 00:07:50,820 --> 00:07:53,050 You've got the evidence laid out in front of you... 119 00:07:57,190 --> 00:08:00,360 and we have to figure out who done it. 120 00:08:16,610 --> 00:08:20,610 Our home in the universe is dying... 121 00:08:20,610 --> 00:08:26,980 Not the Earth, but our galaxy, the Milky Way. 122 00:08:26,980 --> 00:08:30,520 It's been producing stars for billions of years, 123 00:08:30,520 --> 00:08:32,990 but soon, it will stop. 124 00:08:35,060 --> 00:08:37,730 Our own sun formed about 4 1/2 billion years ago 125 00:08:37,730 --> 00:08:39,130 in the Milky Way galaxy, 126 00:08:39,130 --> 00:08:42,400 and we are not the oldest star by far. 127 00:08:42,400 --> 00:08:44,600 And yet, tragically, we actually seem to be 128 00:08:44,600 --> 00:08:48,340 one of the last generations of new stars in the Milky Way. 129 00:08:48,340 --> 00:08:51,770 Current projections suggest that in about 4 billion years, 130 00:08:51,780 --> 00:08:53,780 star formation may have ceased all together, 131 00:08:53,780 --> 00:08:55,640 which is almost just a blink of an eye 132 00:08:55,650 --> 00:08:57,550 in the life cycle of the universe. 133 00:09:01,920 --> 00:09:05,890 To find out why, scientists launch an investigation. 134 00:09:05,890 --> 00:09:08,190 The most crucial question? 135 00:09:08,190 --> 00:09:11,060 How is the milky way dying? 136 00:09:12,900 --> 00:09:16,130 To kill a galaxy, you have to get rid of the cold gas, 137 00:09:16,130 --> 00:09:18,330 because that's what stars form from. 138 00:09:18,340 --> 00:09:19,800 There are many ways you can do this. 139 00:09:19,800 --> 00:09:21,900 You can blast it out from the inside. 140 00:09:21,910 --> 00:09:24,110 You can draw it out from the outside. 141 00:09:24,110 --> 00:09:26,510 You can heat it up so it's no longer cold. 142 00:09:26,510 --> 00:09:28,010 You can use it all up, 143 00:09:28,010 --> 00:09:30,150 and there's even more ways you can stop it. 144 00:09:30,150 --> 00:09:31,710 What we have to do is figure out 145 00:09:31,720 --> 00:09:34,320 which way is happening in our galaxy. 146 00:09:36,890 --> 00:09:42,420 Perhaps the culprit is inside the Milky Way itself. 147 00:09:42,430 --> 00:09:45,830 A clue comes from another galaxy entirely. 148 00:09:47,860 --> 00:09:54,670 This is w2246-0526. 149 00:09:54,670 --> 00:09:58,670 Scientists call it a hot, dust-obscured galaxy, 150 00:09:58,680 --> 00:10:01,040 or "hot dog" for short. 151 00:10:03,810 --> 00:10:06,920 This galaxy is 12 1/2 billion light-years away. 152 00:10:06,920 --> 00:10:09,780 It's the most luminous galaxy we know of in the universe. 153 00:10:09,790 --> 00:10:12,920 It has the light of 300 trillion stars. 154 00:10:17,190 --> 00:10:20,900 The source of the intense light is not its stars, 155 00:10:20,900 --> 00:10:25,900 but a mysterious object at the galaxy's center. 156 00:10:25,900 --> 00:10:29,400 It's a million times smaller than the galaxy itself. 157 00:10:32,140 --> 00:10:35,980 There's only one thing that small and that powerful... 158 00:10:38,680 --> 00:10:40,920 a supermassive black hole. 159 00:10:44,750 --> 00:10:47,860 So, supermassive black holes, as the name suggests, 160 00:10:47,860 --> 00:10:49,390 are indeed supermassive. 161 00:10:49,390 --> 00:10:53,800 These are billions of times more massive than our sun. 162 00:10:53,800 --> 00:10:55,860 These are gigantic objects. 163 00:10:58,770 --> 00:11:02,940 The gravity in the supermassive black hole is off the charts. 164 00:11:06,480 --> 00:11:08,540 It sucks in incredible amounts 165 00:11:08,550 --> 00:11:11,880 of the hot dog's vital star-forming gas. 166 00:11:15,920 --> 00:11:18,450 And as the gas swirls to form a disk, 167 00:11:18,460 --> 00:11:22,390 the intense friction superheats it to millions of degrees 168 00:11:22,390 --> 00:11:27,160 and, in some galaxies, triggers huge jets. 169 00:11:27,160 --> 00:11:29,560 When a lot of material falls onto that black hole, 170 00:11:29,570 --> 00:11:31,970 it creates incredibly energetic jets 171 00:11:31,970 --> 00:11:34,870 that can be tens of thousands of light-years across. 172 00:11:34,870 --> 00:11:36,940 All of a sudden, you have this blowtorch 173 00:11:36,940 --> 00:11:39,610 in the middle of the galaxy. 174 00:11:39,610 --> 00:11:41,840 Black hole jets are bad for galaxies 175 00:11:41,850 --> 00:11:43,980 because they can shut down star formation. 176 00:11:43,980 --> 00:11:46,580 They can heat gas up, blow gas out of galaxies, 177 00:11:46,580 --> 00:11:48,150 and they could really kill them. 178 00:11:50,490 --> 00:11:54,060 A supermassive black hole is cooking the hot dog. 179 00:11:57,490 --> 00:11:59,260 What's going on in our galaxy? 180 00:12:08,710 --> 00:12:12,870 In 2016, scientists at Harvard discovered damning evidence 181 00:12:12,880 --> 00:12:16,310 that may link the Milky Way's supermassive black hole 182 00:12:16,310 --> 00:12:18,080 to the galaxy's demise. 183 00:12:21,080 --> 00:12:22,550 Just like the hot dog, 184 00:12:22,550 --> 00:12:26,650 the Milky Way is surrounded by a vast cloud of blown-out gas, 185 00:12:28,790 --> 00:12:34,060 and the scientists traced the gas back to its source... 186 00:12:34,060 --> 00:12:39,000 Sagittarius a-star, our supermassive black hole. 187 00:12:42,010 --> 00:12:44,110 Well, it turns out our supermassive black hole 188 00:12:44,110 --> 00:12:47,680 had a bit of a hiccup about 6 million years ago. 189 00:12:47,680 --> 00:12:50,510 There's evidence that some matter must have fallen 190 00:12:50,510 --> 00:12:53,010 into that black hole, and if it fell in too quickly, 191 00:12:53,020 --> 00:12:56,080 it would have gotten superheated by its own friction, 192 00:12:56,090 --> 00:13:00,890 and this would have acted, in a sense, like an explosion. 193 00:13:00,890 --> 00:13:03,220 And that event was huge. 194 00:13:03,230 --> 00:13:06,660 Our galaxy expelled an incredible amount of gas... 195 00:13:06,660 --> 00:13:10,100 130 billion times the mass of the Sun. 196 00:13:10,100 --> 00:13:11,970 Large amount of gas. 197 00:13:14,900 --> 00:13:16,900 This event must have been very catastrophic 198 00:13:16,910 --> 00:13:19,640 for the inner parts of the galaxy. 199 00:13:19,640 --> 00:13:22,380 Luckily, Earth is in the outer parts of the galaxy, 200 00:13:22,380 --> 00:13:24,780 where we were able to survive this event. 201 00:13:28,620 --> 00:13:31,590 Is this the smoking gun? 202 00:13:31,590 --> 00:13:36,720 Is our own supermassive black hole killing the Milky Way? 203 00:13:36,730 --> 00:13:38,990 The evidence seems to mount up. 204 00:13:41,560 --> 00:13:45,530 But Sagittarius a-star has an alibi. 205 00:13:45,540 --> 00:13:48,740 It exploded too late. 206 00:13:48,740 --> 00:13:51,610 Sagittarius a-star got very active, 207 00:13:51,610 --> 00:13:54,040 very explosive about 6 million years ago, 208 00:13:54,040 --> 00:13:56,510 but that's so recent, it shouldn't have really affected 209 00:13:56,510 --> 00:13:57,950 the star formation rates. 210 00:13:57,950 --> 00:13:59,310 Something else is going on. 211 00:13:59,320 --> 00:14:02,180 There must be another culprit besides the black hole. 212 00:14:04,390 --> 00:14:08,420 Studies suggest our supermassive black hole must have been active 213 00:14:08,430 --> 00:14:10,890 hundreds of millions of years ago 214 00:14:10,890 --> 00:14:15,360 to stop all star formation in our galaxy. 215 00:14:15,370 --> 00:14:19,230 Sagittarius a-star wasn't active at that time, 216 00:14:19,240 --> 00:14:22,140 so it's no longer a suspect. 217 00:14:24,210 --> 00:14:27,580 The hunt is on for a different galaxy killer, 218 00:14:27,580 --> 00:14:31,850 and scientists are widening the investigation. 219 00:14:31,850 --> 00:14:34,420 Maybe the killer isn't inside our galaxy. 220 00:14:34,420 --> 00:14:37,620 It could be that we suffered a hit-and-run. 221 00:15:05,010 --> 00:15:07,610 Our universe is a crime scene. 222 00:15:09,910 --> 00:15:15,050 Star production in the Milky Way is breaking down. 223 00:15:15,050 --> 00:15:17,150 Our galaxy is dying, 224 00:15:17,150 --> 00:15:20,790 and astronomers are examining the body for clues. 225 00:15:23,030 --> 00:15:28,600 The Milky Way's disk is made up of three sections... 226 00:15:28,600 --> 00:15:33,300 A nucleus, home to the galaxy's supermassive black hole... 227 00:15:36,210 --> 00:15:41,510 a dense, central bulge 10,000 light-years across, 228 00:15:41,510 --> 00:15:43,180 and the spiral arms... 229 00:15:43,180 --> 00:15:47,020 Full of gas, dust, and billions of stars. 230 00:15:49,090 --> 00:15:53,790 The spiral arms should be flat, but they're rippling. 231 00:15:53,790 --> 00:15:57,060 Is this a clue for the cosmic detectives? 232 00:15:58,860 --> 00:16:00,900 Today, we look at the edge of the Milky Way, 233 00:16:00,900 --> 00:16:02,970 and we see mysterious ripples in its gas, 234 00:16:02,970 --> 00:16:05,170 and we wonder, what's the origin? 235 00:16:05,170 --> 00:16:07,270 Something must have caused it to happen. 236 00:16:07,270 --> 00:16:09,740 Something like that just doesn't happen on its own. 237 00:16:09,740 --> 00:16:11,640 The real question is, why? 238 00:16:16,250 --> 00:16:20,820 Whatever caused the ripples didn't hang around. 239 00:16:20,820 --> 00:16:23,850 Is this evidence of a galactic hit-and-run? 240 00:16:26,920 --> 00:16:29,090 January 2016. 241 00:16:32,060 --> 00:16:36,100 Astronomers studying data from the vista telescope 242 00:16:36,100 --> 00:16:38,100 discover something incredible... 243 00:16:42,210 --> 00:16:44,740 three nearby stars. 244 00:16:44,740 --> 00:16:47,480 On their own, nothing special, 245 00:16:47,480 --> 00:16:51,080 except they've recently left our galaxy, 246 00:16:51,080 --> 00:16:55,650 and they're traveling at 350,000 miles an hour. 247 00:16:59,420 --> 00:17:01,860 So, we've discovered these stars that are careening 248 00:17:01,860 --> 00:17:04,630 out of the galaxy at super-high velocities. 249 00:17:04,630 --> 00:17:06,900 Could these three stars somehow be responsible 250 00:17:06,900 --> 00:17:08,800 for warping the Milky Way's disk? 251 00:17:08,800 --> 00:17:10,270 Well, absolutely not. 252 00:17:10,270 --> 00:17:13,500 The Milky Way is so much more massive than just three stars. 253 00:17:13,500 --> 00:17:16,910 Three stars alone can't warp a galaxy, 254 00:17:16,910 --> 00:17:20,280 but those three stars can be indicative of more stars. 255 00:17:20,280 --> 00:17:22,780 They can be indicative of the presence of, say, 256 00:17:22,780 --> 00:17:25,980 a dwarf galaxy, and that can warp the galaxy. 257 00:17:27,950 --> 00:17:31,390 Dwarf galaxies are abundant. 258 00:17:31,390 --> 00:17:34,690 But a tiny fraction of the size of a major galaxy, 259 00:17:34,690 --> 00:17:36,260 like the Milky Way. 260 00:17:38,330 --> 00:17:41,700 So they're difficult to detect. 261 00:17:41,700 --> 00:17:45,900 But these three bright stars show there's a dwarf galaxy 262 00:17:45,900 --> 00:17:50,210 hiding beyond the edge of the Milky Way. 263 00:17:50,210 --> 00:17:53,340 And scientists can study the trio of stars 264 00:17:53,340 --> 00:17:55,080 to rewind the clock 265 00:17:55,080 --> 00:17:59,280 and track back the past movements of the dwarf galaxy. 266 00:18:02,150 --> 00:18:04,950 Simulations suggest that millions of years ago, 267 00:18:04,960 --> 00:18:06,220 this dwarf galaxy 268 00:18:06,220 --> 00:18:08,290 punched through the plane of the Milky Way. 269 00:18:13,230 --> 00:18:18,000 As the fast-moving dwarf galaxy hurtles towards the Milky Way, 270 00:18:18,000 --> 00:18:23,740 millions of stars seem set on a collision course. 271 00:18:23,740 --> 00:18:26,070 Catastrophe looks inevitable. 272 00:18:27,980 --> 00:18:30,980 But appearances can be deceptive. 273 00:18:32,850 --> 00:18:35,320 When galaxies collide, the first thing you might imagine 274 00:18:35,320 --> 00:18:37,950 is that the stars collide, but actually, that doesn't happen. 275 00:18:37,960 --> 00:18:39,760 Galaxies are mostly empty space. 276 00:18:39,760 --> 00:18:41,960 If you took the Sun, which is really big... 277 00:18:41,960 --> 00:18:43,690 It's a million miles across... 278 00:18:43,690 --> 00:18:47,660 And shrunk it down to the size of a piece of pollen, 279 00:18:47,660 --> 00:18:51,030 the galaxy itself would be twice the size of the pacific ocean, 280 00:18:51,040 --> 00:18:54,500 and the nearest star to the Sun would be a mile away. 281 00:18:54,510 --> 00:18:57,670 Those tiny pieces of pollen are never going to hit each other. 282 00:19:01,610 --> 00:19:05,750 The distances involved are staggering. 283 00:19:05,750 --> 00:19:07,420 And at the moment of impact, 284 00:19:07,420 --> 00:19:09,990 most of the stars from the two galaxies 285 00:19:09,990 --> 00:19:12,620 miss each other entirely. 286 00:19:12,620 --> 00:19:16,660 But that doesn't mean the Milky Way is safe. 287 00:19:18,830 --> 00:19:21,600 Even though the stars just pass each other, 288 00:19:21,600 --> 00:19:25,430 they do gravitationally interact as they come close, 289 00:19:25,440 --> 00:19:28,800 and this gravitational interaction sets them 290 00:19:28,810 --> 00:19:30,410 on a course that is different 291 00:19:30,410 --> 00:19:32,840 than if they were to live by themselves. 292 00:19:35,680 --> 00:19:37,780 In much the same way that taking a stone 293 00:19:37,780 --> 00:19:39,450 and dropping it into a still pond 294 00:19:39,450 --> 00:19:41,580 creates ripples in the water, 295 00:19:41,590 --> 00:19:44,250 a galaxy like this slamming into the Milky Way 296 00:19:44,250 --> 00:19:46,660 can create ripple effects throughout the disk. 297 00:19:49,960 --> 00:19:51,630 The ripples in the Milky Way 298 00:19:51,630 --> 00:19:55,030 stretch across tens of thousands of light-years. 299 00:19:57,200 --> 00:20:02,540 Still, this hit-and-run isn't enough to kill the Milky Way. 300 00:20:02,540 --> 00:20:06,210 It only causes a flesh wound. 301 00:20:06,210 --> 00:20:11,710 But what if this dwarf galaxy isn't acting alone? 302 00:20:11,720 --> 00:20:13,680 What if it has accomplices? 303 00:20:16,220 --> 00:20:18,950 There are a lot of dwarf galaxies out there, 304 00:20:18,960 --> 00:20:22,220 and it turns out collisions between these dwarf galaxies 305 00:20:22,230 --> 00:20:25,090 and big galaxies, like the Milky Way, are common. 306 00:20:25,100 --> 00:20:26,360 They happen all the time. 307 00:20:26,360 --> 00:20:28,400 Right now, there are several dwarf galaxies 308 00:20:28,400 --> 00:20:30,430 that the Milky Way is swallowing up. 309 00:20:30,430 --> 00:20:32,630 In fact, a really fun thing is that we're actually closer 310 00:20:32,640 --> 00:20:34,800 to the core of one of these galaxies... 311 00:20:34,810 --> 00:20:36,740 The Canis Majoris dwarf galaxy... 312 00:20:36,740 --> 00:20:38,570 Than we are to the core of the Milky Way. 313 00:20:38,580 --> 00:20:41,510 So some of the stars that you see around you in the night sky 314 00:20:41,510 --> 00:20:44,250 are actually stars from a different galaxy. 315 00:20:44,250 --> 00:20:47,350 So, what happens when all these dwarf galaxies come together 316 00:20:47,350 --> 00:20:50,220 and start pulling and tugging on a larger galaxy? 317 00:20:56,030 --> 00:20:59,860 Cosmologists believe there could be hundreds of dwarf galaxies 318 00:20:59,860 --> 00:21:02,400 surrounding the Milky Way. 319 00:21:05,240 --> 00:21:08,740 A collision with just one of these dwarf galaxies 320 00:21:08,740 --> 00:21:12,470 may have rippled the Milky Way's spiral arms, 321 00:21:14,480 --> 00:21:17,680 but a gang of dwarf galaxies 322 00:21:17,680 --> 00:21:23,190 could have a far bigger and far more deadly effect. 323 00:21:23,190 --> 00:21:25,490 Dwarf galaxies and the way they interact with big galaxies, 324 00:21:25,490 --> 00:21:26,720 like the Milky Way, 325 00:21:26,720 --> 00:21:29,690 can inflect tremendous change in our universe. 326 00:21:29,690 --> 00:21:32,330 When they slam into a galaxy, they can change its structure. 327 00:21:32,330 --> 00:21:35,160 The Milky Way would not look anything like it looks today 328 00:21:35,170 --> 00:21:38,200 without those dwarf galaxies. 329 00:21:38,200 --> 00:21:40,940 Repeated dwarf-galaxy collisions 330 00:21:40,940 --> 00:21:44,640 could have radically altered the shape of the Milky Way itself. 331 00:21:47,240 --> 00:21:51,010 Their gravitational disruptions could have created a distinctive 332 00:21:51,010 --> 00:21:55,080 and possibly fatal feature in the middle of our galaxy... 333 00:21:55,090 --> 00:21:56,590 The galactic bar. 334 00:21:59,990 --> 00:22:02,260 The center of the Milky Way is elongated. 335 00:22:02,260 --> 00:22:04,160 Instead of it being shaped like a sphere, 336 00:22:04,160 --> 00:22:07,330 it's more shaped like a bar, and the bar is made by stars 337 00:22:07,330 --> 00:22:11,470 actually orbiting in this sort of elongated way. 338 00:22:11,470 --> 00:22:14,340 And this bar can be bad for the health of the galaxy 339 00:22:14,340 --> 00:22:16,910 because what they do is help to funnel gas 340 00:22:16,910 --> 00:22:18,740 into the core of the galaxy. 341 00:22:18,740 --> 00:22:23,140 The loss of this gas could be a way of stopping star formation. 342 00:22:26,620 --> 00:22:29,820 The bar-shaped bulge at the center of the Milky Way 343 00:22:29,820 --> 00:22:32,790 sweeps our galaxy's star-building gas 344 00:22:32,790 --> 00:22:35,020 into the galactic nucleus. 345 00:22:35,030 --> 00:22:36,630 Here, it gets gobbled up 346 00:22:36,630 --> 00:22:39,460 by our galaxy's supermassive black hole. 347 00:22:43,530 --> 00:22:47,700 Without the star-building material, no new stars can form, 348 00:22:47,700 --> 00:22:51,140 and the galaxy dies. 349 00:22:51,140 --> 00:22:53,170 So, is it case closed? 350 00:22:53,180 --> 00:22:55,740 Are dwarf galaxies killing the Milky Way? 351 00:22:55,750 --> 00:22:59,780 Is the murder weapon a galactic bar? 352 00:22:59,780 --> 00:23:02,650 So, it's possible that the formation of these bars 353 00:23:02,650 --> 00:23:06,350 helps turn off star formation in the very core of the galaxy, 354 00:23:06,360 --> 00:23:09,260 but that's just the central regions of the galaxy. 355 00:23:09,260 --> 00:23:11,130 That doesn't explain what's going farther out 356 00:23:11,130 --> 00:23:12,960 in the spiral arms. 357 00:23:12,960 --> 00:23:16,460 So, if star formation really is shutting down in the Milky Way, 358 00:23:16,470 --> 00:23:18,770 it's not really the fault of the bar. 359 00:23:20,940 --> 00:23:25,310 Dwarf galaxies cause the Milky Way grievous bodily harm 360 00:23:25,310 --> 00:23:28,380 by creating the galactic bar. 361 00:23:28,380 --> 00:23:33,820 But they're off the hook for attempted galactic murder. 362 00:23:33,820 --> 00:23:36,550 The investigation continues, 363 00:23:36,550 --> 00:23:41,760 and it could be about to take a dramatic twist. 364 00:23:41,760 --> 00:23:44,030 It might not be that the galaxy's being murdered. 365 00:23:44,030 --> 00:23:46,330 It could just be eating itself to death. 366 00:24:11,850 --> 00:24:15,850 The Milky Way is being killed off. 367 00:24:15,850 --> 00:24:18,620 And the perpetrator remains at large. 368 00:24:20,790 --> 00:24:22,760 Scientists investigating the crime 369 00:24:22,760 --> 00:24:24,490 are running out of suspects. 370 00:24:26,530 --> 00:24:28,660 But the hunt for clues continues, 371 00:24:30,640 --> 00:24:35,870 so astronomers are examining the dying body of the Milky Way. 372 00:24:35,870 --> 00:24:39,040 Our galaxy is a hazy disk of stars 373 00:24:39,040 --> 00:24:42,610 surrounded by a halo of superheated gas. 374 00:24:44,480 --> 00:24:48,450 It's over 100,000 light-years across. 375 00:24:48,450 --> 00:24:50,620 But it hasn't always been so big. 376 00:24:52,890 --> 00:24:55,090 When you think about things so vast, 377 00:24:55,090 --> 00:24:57,130 so gigantic and ancient as galaxies, 378 00:24:57,130 --> 00:24:58,590 you're kind of tempted to think 379 00:24:58,600 --> 00:25:00,160 that they're very stable objects, 380 00:25:00,170 --> 00:25:02,130 that they don't change much over time, 381 00:25:02,130 --> 00:25:03,930 but we now know that our own galaxy 382 00:25:03,940 --> 00:25:05,870 is the product of many smaller galaxies 383 00:25:05,870 --> 00:25:07,670 that came together over time, 384 00:25:07,670 --> 00:25:10,370 and there are other galaxies still colliding with us. 385 00:25:13,340 --> 00:25:15,610 We see galaxies eating each other all the time. 386 00:25:15,610 --> 00:25:18,310 They collide, and if one galaxy is very big 387 00:25:18,320 --> 00:25:20,180 and one galaxy is very small, 388 00:25:20,190 --> 00:25:23,450 the little galaxy falls into the big one, gets torn apart, 389 00:25:23,450 --> 00:25:27,560 and becomes a part of that bigger galaxy. 390 00:25:27,560 --> 00:25:29,890 The Milky Way might be dying, 391 00:25:29,890 --> 00:25:33,360 but it's still a monster foraging through the universe, 392 00:25:33,360 --> 00:25:35,730 swallowing smaller galaxies whole. 393 00:25:39,300 --> 00:25:41,370 It consumes their stars. 394 00:25:41,370 --> 00:25:45,440 But it also has a taste for their star-building gas. 395 00:25:47,310 --> 00:25:50,650 And it doesn't have to collide with other galaxies 396 00:25:50,650 --> 00:25:53,980 to feed off of them. 397 00:25:53,990 --> 00:25:56,790 Now, the lifeblood of a galaxy is hydrogen gas. 398 00:25:56,790 --> 00:25:59,060 That's what actually creates new stars. 399 00:25:59,060 --> 00:26:02,020 So as a dwarf galaxy passes by the Milky Way, 400 00:26:02,030 --> 00:26:05,230 the tremendously massive halo of the Milky Way, 401 00:26:05,230 --> 00:26:08,600 all of that gas, can draw off material from the dwarf galaxy, 402 00:26:08,600 --> 00:26:10,670 adding it to the Milky Way. 403 00:26:10,670 --> 00:26:12,900 So in this way, the Milky Way drains away 404 00:26:12,900 --> 00:26:15,940 the lifeblood of other galaxies. 405 00:26:15,940 --> 00:26:18,510 In some sense, you could say it's a vampire 406 00:26:18,510 --> 00:26:21,310 because a vampire sucks the life out of other things 407 00:26:21,310 --> 00:26:22,750 so it can remain young. 408 00:26:26,680 --> 00:26:33,990 In its 13 billion-year life, our vampire galaxy has feasted. 409 00:26:33,990 --> 00:26:37,260 Consuming the lifeblood of its galactic victims, 410 00:26:37,260 --> 00:26:40,100 the Milky Way has grown fat. 411 00:26:42,530 --> 00:26:45,670 But could this monstrous feeding frenzy be a factor 412 00:26:45,670 --> 00:26:47,500 in the Milky Way's demise? 413 00:26:50,410 --> 00:26:52,310 Once again, crucial evidence 414 00:26:52,310 --> 00:26:56,910 comes from the Sloan digital sky survey. 415 00:26:56,920 --> 00:26:59,980 Their telescope maps the stars in our galaxy, 416 00:26:59,980 --> 00:27:03,790 but it also maps the galaxies in our universe. 417 00:27:06,260 --> 00:27:11,760 Looking at distant galaxies is like looking back in time. 418 00:27:11,760 --> 00:27:14,160 Because the farther away they are, 419 00:27:14,170 --> 00:27:16,930 the longer their light takes to reach us. 420 00:27:19,800 --> 00:27:24,740 We see the most distant galaxies not as they are now, 421 00:27:24,740 --> 00:27:29,410 but as they were... Billions of years ago. 422 00:27:29,410 --> 00:27:30,850 So, when you look at these galaxies, 423 00:27:30,850 --> 00:27:33,120 you're seeing them as they were when they were very young, 424 00:27:33,120 --> 00:27:36,120 and you're seeing these galaxies as they are more recently, 425 00:27:36,120 --> 00:27:38,490 so you can actually look at the evolution... 426 00:27:38,490 --> 00:27:42,390 How galaxies change over time as the universe ages. 427 00:27:44,530 --> 00:27:46,100 While studying the data, 428 00:27:46,100 --> 00:27:49,100 scientists make a dramatic discovery. 429 00:27:49,100 --> 00:27:53,670 They find spiral galaxies, just like the Milky Way, 430 00:27:53,670 --> 00:27:57,410 dying all over the universe. 431 00:27:57,410 --> 00:28:00,240 And what connects them is their mass. 432 00:28:02,280 --> 00:28:03,850 There seems to be an upper weight limit 433 00:28:03,850 --> 00:28:06,680 for the sizes of spiral galaxies. 434 00:28:06,680 --> 00:28:09,150 Up to about a trillion times the mass of the Sun, 435 00:28:09,150 --> 00:28:12,050 we see spiral galaxies that continue to form stars, 436 00:28:12,060 --> 00:28:14,020 but once they pass this threshold, 437 00:28:14,030 --> 00:28:16,430 galaxies tend to die and run out of stars. 438 00:28:18,600 --> 00:28:20,700 While devouring the star-building gas 439 00:28:20,700 --> 00:28:22,900 of smaller galaxies, 440 00:28:22,900 --> 00:28:26,000 the Milky Way may have grown obese, 441 00:28:26,000 --> 00:28:30,010 and now it could be choking to death on its own dinner. 442 00:28:30,010 --> 00:28:32,270 But how? 443 00:28:32,280 --> 00:28:34,980 Once a spiral galaxy is sufficiently big, 444 00:28:34,980 --> 00:28:37,580 it's going to have an incredible gravitational force, 445 00:28:37,580 --> 00:28:39,980 so any gas that it pulls to itself 446 00:28:39,980 --> 00:28:43,550 is going to come in at an incredibly high speed. 447 00:28:43,550 --> 00:28:45,760 That gas is going to be superheated. 448 00:28:49,660 --> 00:28:52,290 The superheated gas moves so quickly 449 00:28:52,300 --> 00:28:56,400 that it's prevented from falling into the Milky Way. 450 00:28:56,400 --> 00:29:01,570 The gas is too energetic for our galaxy's gravity to pull it in. 451 00:29:01,570 --> 00:29:05,780 Instead, it stays in the halo around the Milky Way, 452 00:29:05,780 --> 00:29:10,510 and our galaxy's food supply is choked off. 453 00:29:10,520 --> 00:29:14,950 Eventually, our galaxy will starve. 454 00:29:14,950 --> 00:29:16,850 This will only happen if the Milky Way 455 00:29:16,850 --> 00:29:20,290 is over the star-building weight limit. 456 00:29:20,290 --> 00:29:24,830 But how exactly do you weigh a galaxy? 457 00:29:24,830 --> 00:29:27,300 One basic way we can weigh a galaxy 458 00:29:27,300 --> 00:29:30,000 is measure how fast the stars are moving within it. 459 00:29:30,000 --> 00:29:32,940 So the faster the stars orbit around the center of the galaxy, 460 00:29:32,940 --> 00:29:35,810 the more massive the galaxy is. 461 00:29:35,810 --> 00:29:40,110 This method of weighing the Milky Way relies on gravity. 462 00:29:40,110 --> 00:29:43,380 Fast-moving stars need more gravity to hold them 463 00:29:43,380 --> 00:29:44,710 in their orbits, 464 00:29:44,720 --> 00:29:49,590 and more gravity means more galactic mass. 465 00:29:49,590 --> 00:29:53,690 When scientists use this information to run the math, 466 00:29:53,690 --> 00:29:57,230 the horrible truth is revealed. 467 00:29:57,230 --> 00:29:59,930 We've passed kind of a critical level. 468 00:29:59,930 --> 00:30:03,500 The Milky Way is far too massive for its own health, 469 00:30:03,500 --> 00:30:06,340 and we've entered the beginning of the end. 470 00:30:06,340 --> 00:30:09,540 We're running out of gas, and I mean this literally. 471 00:30:09,540 --> 00:30:11,410 Gas clouds form stars, 472 00:30:11,410 --> 00:30:14,840 and as they form stars, they're used up, 473 00:30:14,850 --> 00:30:17,080 and so our gas tank is getting closer and closer 474 00:30:17,080 --> 00:30:19,580 to empty every day. 475 00:30:23,350 --> 00:30:26,390 The investigation into the killing of the Milky Way 476 00:30:26,390 --> 00:30:27,760 is closed. 477 00:30:29,960 --> 00:30:31,330 The verdict? 478 00:30:31,330 --> 00:30:35,130 The greedy Milky Way is killing itself. 479 00:30:37,770 --> 00:30:41,770 Over millions of years, star formation grinds to a halt, 480 00:30:41,770 --> 00:30:43,670 and the galaxy dies. 481 00:30:46,310 --> 00:30:51,450 But could the galaxy be resurrected? 482 00:30:51,450 --> 00:30:53,320 We seem to be telling a very sad story. 483 00:30:53,320 --> 00:30:55,520 We're talking about the demise of the Milky Way galaxy... 484 00:30:55,520 --> 00:30:57,290 The end of star formation... 485 00:30:57,290 --> 00:30:59,120 But maybe it's just a little bit too soon 486 00:30:59,120 --> 00:31:00,890 to write the death announcement yet. 487 00:31:00,890 --> 00:31:03,390 Hope could be just over the horizon. 488 00:31:06,230 --> 00:31:09,470 In space and astrophysics, really anything is possible. 489 00:31:30,980 --> 00:31:35,750 The shocking case of our dying galaxy has been solved. 490 00:31:35,750 --> 00:31:38,090 There was no killer. 491 00:31:38,090 --> 00:31:41,760 Turns out, the Milky Way is eating itself to death. 492 00:31:46,000 --> 00:31:49,470 But is this really the end? 493 00:31:49,470 --> 00:31:52,440 Could salvation be heading our way? 494 00:31:54,340 --> 00:31:56,210 Even if star formation is turning off 495 00:31:56,210 --> 00:31:57,570 in the Milky Way now, 496 00:31:57,580 --> 00:31:59,380 we know that it's on a collision course 497 00:31:59,380 --> 00:32:01,340 with the Andromeda galaxy. 498 00:32:01,350 --> 00:32:02,510 They're moving toward each other 499 00:32:02,510 --> 00:32:06,820 at hundreds of thousands of miles per hour. 500 00:32:06,820 --> 00:32:08,320 A collision sounds like something 501 00:32:08,320 --> 00:32:09,850 that's always destructive, 502 00:32:09,860 --> 00:32:11,860 but that's not necessarily the case. 503 00:32:14,790 --> 00:32:15,990 The Milky Way's collision 504 00:32:15,990 --> 00:32:19,930 with our giant galactic neighbor Andromeda 505 00:32:19,930 --> 00:32:23,100 won't happen for another 4 billion years. 506 00:32:25,440 --> 00:32:29,070 By then, star formation in both of these galaxies 507 00:32:29,070 --> 00:32:30,770 will have stopped completely. 508 00:32:33,550 --> 00:32:37,550 But a giant meet-up could change all that. 509 00:32:40,820 --> 00:32:42,290 As an isolated galaxy, 510 00:32:42,290 --> 00:32:45,690 the Milky Way is already in its wind-down phase. 511 00:32:45,690 --> 00:32:49,360 It's not producing as many new stars as it used to. 512 00:32:49,360 --> 00:32:53,530 But there is one way to generate a new round of star formation, 513 00:32:53,530 --> 00:32:57,230 and that's through a galactic merger event. 514 00:32:57,240 --> 00:32:59,200 When Andromeda gets close enough, 515 00:32:59,200 --> 00:33:01,300 the mutual gravity between the two galaxies 516 00:33:01,310 --> 00:33:05,610 will start to stretch them out, pulling them out like Taffy. 517 00:33:05,610 --> 00:33:08,550 Stars will be pulled out into these long, looping streamers, 518 00:33:08,550 --> 00:33:09,680 and then the galaxies 519 00:33:09,680 --> 00:33:12,850 will physically pass through each other. 520 00:33:12,850 --> 00:33:16,620 Eventually, the two galaxies will draw back together again 521 00:33:16,620 --> 00:33:19,260 and merge into one gigantic galaxy, 522 00:33:19,260 --> 00:33:21,190 and at that point, all of these gas clouds 523 00:33:21,190 --> 00:33:24,360 will flash into star formation. 524 00:33:29,070 --> 00:33:33,600 As the galaxies merge, they'll be reborn. 525 00:33:33,610 --> 00:33:36,570 Two dying spiral-shaped galaxies 526 00:33:36,580 --> 00:33:40,840 become a single living elliptical galaxy 527 00:33:40,850 --> 00:33:44,850 called Milkomeda. 528 00:33:44,850 --> 00:33:47,450 Imagine you're living in the far future of the galaxy 529 00:33:47,450 --> 00:33:49,050 and you see the night sky 530 00:33:49,050 --> 00:33:51,620 while the Milky Way and Andromeda are colliding. 531 00:33:51,620 --> 00:33:53,920 It will look like a very different place. 532 00:33:53,930 --> 00:33:56,160 Rather than one band across the night sky, 533 00:33:56,160 --> 00:33:58,900 you might have two as the two disks come together. 534 00:33:58,900 --> 00:34:00,560 It will be a miraculous sight, 535 00:34:00,570 --> 00:34:03,400 but a very, very different place than we have today. 536 00:34:06,710 --> 00:34:11,880 Our sky will light up for the first time in billions of years. 537 00:34:11,880 --> 00:34:15,310 Star formation will flare across the galaxy. 538 00:34:17,650 --> 00:34:20,550 But is it too soon to celebrate? 539 00:34:24,290 --> 00:34:26,660 This new round of star formation 540 00:34:26,660 --> 00:34:30,490 during the merger of our two galaxies... 541 00:34:30,500 --> 00:34:32,860 While it's very cool for a little bit, 542 00:34:32,870 --> 00:34:37,600 once it's over, that kind of sends the new galaxy 543 00:34:37,600 --> 00:34:39,000 into a death spiral. 544 00:34:39,000 --> 00:34:41,770 When new stars are born in this new galaxy, 545 00:34:41,770 --> 00:34:46,080 many of them are going to be hot, large, blue stars. 546 00:34:46,080 --> 00:34:49,280 Eventually, those young, hot stars are going to start to die, 547 00:34:49,280 --> 00:34:51,380 and when they do, they're going to explode 548 00:34:51,380 --> 00:34:53,380 violently as supernovae. 549 00:34:58,860 --> 00:35:00,860 And those supernovae are going to start 550 00:35:00,860 --> 00:35:03,390 blasting gas out of the galaxy. 551 00:35:07,070 --> 00:35:08,600 All of the gas is gone. 552 00:35:08,600 --> 00:35:10,900 There's no more stuff to form stars. 553 00:35:10,900 --> 00:35:12,670 And that's what kills a galaxy. 554 00:35:16,440 --> 00:35:18,740 It'll take hundreds of millions of years 555 00:35:18,740 --> 00:35:23,350 for Milkomeda to run out of star-building gas. 556 00:35:23,350 --> 00:35:27,650 And then our new elliptical galaxy will starve. 557 00:35:29,450 --> 00:35:32,060 But the final blow is still to come. 558 00:35:34,490 --> 00:35:36,730 Another issue to consider is what happens 559 00:35:36,730 --> 00:35:38,760 to the two supermassive black holes 560 00:35:38,760 --> 00:35:41,460 at the cores of the two galaxies. 561 00:35:41,470 --> 00:35:44,000 Well, initially, they're going to orbit each other, 562 00:35:44,000 --> 00:35:48,570 stirring up a lot of turbulence, and they're going to combine. 563 00:35:48,570 --> 00:35:51,510 And because there's a lot of new, hot, fresh gas, 564 00:35:51,510 --> 00:35:54,680 our new galaxy is going to be a quasar. 565 00:35:54,680 --> 00:35:57,210 And that quasar is going to turn up the heat, 566 00:35:57,220 --> 00:35:58,850 it's going to turn up the turbulence, 567 00:35:58,850 --> 00:36:02,090 and this means star formation is going to be shut off. 568 00:36:04,360 --> 00:36:07,960 The combined power of the supermassive black holes 569 00:36:07,960 --> 00:36:11,960 help create a quasar that tears through the galaxy. 570 00:36:15,070 --> 00:36:18,270 It releases ferocious beams of radiation 571 00:36:18,270 --> 00:36:21,840 that blast through Milkomeda's star-forming gas. 572 00:36:25,180 --> 00:36:27,080 It's only just been reborn, 573 00:36:27,080 --> 00:36:31,650 but our newly enlarged galaxy is once again dying. 574 00:36:34,350 --> 00:36:39,520 Vast galaxies, like Milkomeda, seem doomed from the start. 575 00:36:39,520 --> 00:36:43,630 Their size creates too many problems for star formation. 576 00:36:46,130 --> 00:36:49,400 Or... so we thought. 577 00:36:49,400 --> 00:36:51,740 The more galaxies we see, the more we realize 578 00:36:51,740 --> 00:36:53,800 there's a lot out there we haven't discovered, 579 00:36:53,810 --> 00:36:55,570 and there's a new class of galaxies 580 00:36:55,570 --> 00:36:57,970 only recently identified. 581 00:36:57,980 --> 00:37:02,580 These galaxies are more than 10 times the mass of the Milky Way. 582 00:37:02,580 --> 00:37:06,680 And, intriguingly, they're still forming stars. 583 00:37:06,690 --> 00:37:08,420 Apparently we've missed something. 584 00:37:32,240 --> 00:37:37,480 4 billion years from now, the Milky Way is no more. 585 00:37:37,480 --> 00:37:40,610 After colliding with Andromeda, it's reborn 586 00:37:40,610 --> 00:37:44,520 as a giant elliptical galaxy called Milkomeda. 587 00:37:46,450 --> 00:37:50,890 Scientists thought galaxies this big were doomed. 588 00:37:50,890 --> 00:37:53,960 But is hope on the horizon? 589 00:37:56,430 --> 00:38:00,000 The Sloan digital sky survey has spent a decade 590 00:38:00,000 --> 00:38:04,570 studying over a million galaxies. 591 00:38:04,570 --> 00:38:08,970 It's discovered a rare but enormous kind of galaxy... 592 00:38:08,980 --> 00:38:10,740 A super spiral. 593 00:38:13,650 --> 00:38:16,580 These super-spiral galaxies are spiral galaxies 594 00:38:16,580 --> 00:38:18,150 that are incredibly super, 595 00:38:18,150 --> 00:38:21,920 and by "super," I mean they have four times the size, 596 00:38:21,920 --> 00:38:23,620 10 times the mass, 597 00:38:23,620 --> 00:38:25,290 and they're weird because they exceed 598 00:38:25,290 --> 00:38:28,290 the supposed weight limit for spiral galaxies. 599 00:38:28,300 --> 00:38:31,300 So they shouldn't have new stars, but they do. 600 00:38:31,300 --> 00:38:33,630 They're very healthy galaxies. 601 00:38:39,240 --> 00:38:43,140 Scientists have found just 53 super spirals. 602 00:38:46,250 --> 00:38:50,350 Super-spiral galaxies show that in rare situations, 603 00:38:50,350 --> 00:38:54,920 massive galaxies continue to produce new stars. 604 00:38:58,790 --> 00:39:02,330 So, is this a lifeline for Milkomeda? 605 00:39:05,170 --> 00:39:07,200 When we think about two galaxies colliding, 606 00:39:07,200 --> 00:39:08,830 a lot of our computer models suggest 607 00:39:08,840 --> 00:39:10,440 that they really mess each other up. 608 00:39:10,440 --> 00:39:12,140 Things get very chaotic. 609 00:39:12,140 --> 00:39:15,970 But over time, could they settle back down into a spiral shape? 610 00:39:15,980 --> 00:39:18,840 And, in fact, that may be what happens with super spirals. 611 00:39:18,850 --> 00:39:21,410 One of the clues is that many super-spiral galaxies 612 00:39:21,410 --> 00:39:22,950 have double cores. 613 00:39:22,950 --> 00:39:25,420 Instead of there just being one supermassive black hole, 614 00:39:25,420 --> 00:39:29,250 there are actually two orbiting each other. 615 00:39:29,260 --> 00:39:31,860 The fact that we see spiral galaxies with two cores 616 00:39:31,860 --> 00:39:33,890 makes it possible that you could have a collision 617 00:39:33,890 --> 00:39:36,430 and still survive as a spiral galaxy. 618 00:39:36,430 --> 00:39:39,400 So maybe there's hope that even the Milky Way will be a spiral 619 00:39:39,400 --> 00:39:41,430 once it collides with Andromeda. 620 00:39:45,640 --> 00:39:49,440 Picture the scene... 6 billion years in the future. 621 00:39:51,640 --> 00:39:54,250 Milkomeda drifts through the universe... 622 00:39:56,220 --> 00:40:00,250 not as an elliptical galaxy, but as a super spiral. 623 00:40:02,820 --> 00:40:07,490 This shape means the galaxy is far more stable. 624 00:40:07,490 --> 00:40:09,530 The damaging heat and turbulence 625 00:40:09,530 --> 00:40:13,030 generated by Milkomeda's supermassive black holes 626 00:40:13,030 --> 00:40:19,070 can't disrupt star-building gas way out in the spiral arms. 627 00:40:19,070 --> 00:40:24,910 Far from dying off, our galaxy lives on... 628 00:40:24,910 --> 00:40:28,610 Larger than ever before. 629 00:40:28,620 --> 00:40:31,880 But that isn't the end of the story. 630 00:40:31,890 --> 00:40:34,990 Tens of billions of years from now, 631 00:40:34,990 --> 00:40:38,960 could the galaxy continue to grow? 632 00:40:38,960 --> 00:40:41,190 Our local group of galaxies... 633 00:40:41,190 --> 00:40:43,730 Milky Way, Andromeda, Triangulum... 634 00:40:43,730 --> 00:40:47,470 And then a collection of dwarf satellite galaxies... 635 00:40:47,470 --> 00:40:50,540 Is gravitationally bound together, 636 00:40:50,540 --> 00:40:53,140 and eventually, we're all glued together 637 00:40:53,140 --> 00:40:55,340 into a single massive object. 638 00:40:57,080 --> 00:40:58,540 What does this mean? 639 00:40:58,550 --> 00:41:00,980 This means we might be part of one of the largest structures 640 00:41:00,980 --> 00:41:03,180 in the universe. 641 00:41:03,180 --> 00:41:05,450 During its billion years of life, 642 00:41:05,450 --> 00:41:10,050 the Milky Way changes beyond recognition. 643 00:41:10,060 --> 00:41:13,390 It suffers countless collisions, 644 00:41:13,390 --> 00:41:17,560 feasts on many smaller galaxies, 645 00:41:17,560 --> 00:41:20,630 and gives birth to innumerable stars. 646 00:41:22,840 --> 00:41:24,900 We talk about the life cycle of galaxies... 647 00:41:24,900 --> 00:41:28,110 How they're born, how they live healthy lives making new stars, 648 00:41:28,110 --> 00:41:30,210 and eventually how they die away. 649 00:41:30,210 --> 00:41:32,380 It's really not as depressing as that. 650 00:41:32,380 --> 00:41:34,480 Everything in the universe changes. 651 00:41:36,550 --> 00:41:41,850 Galaxies like ours are in a constant state of flux. 652 00:41:41,860 --> 00:41:44,660 So when it comes to the Milky Way, 653 00:41:44,660 --> 00:41:47,290 death really isn't the end. 654 00:41:49,200 --> 00:41:50,760 What we see in our universe 655 00:41:50,760 --> 00:41:54,530 is that there's always a process of birth and rebirth, 656 00:41:54,530 --> 00:41:56,100 so the future of the Milky Way 657 00:41:56,100 --> 00:41:58,400 is that it's going to keep on doing what it does. 658 00:42:01,040 --> 00:42:02,740 Galaxies are ever-changing. 659 00:42:02,740 --> 00:42:04,180 10 billion years ago, the Milky Way 660 00:42:04,180 --> 00:42:06,010 was nothing like what it is today, 661 00:42:06,010 --> 00:42:08,010 and certainly, 10 billion years in the future, 662 00:42:08,010 --> 00:42:09,850 it'll be a very different place. 663 00:42:12,420 --> 00:42:14,790 Look, I live in this galaxy. 664 00:42:14,790 --> 00:42:17,390 I hope that it can find a way to rejuvenate itself 665 00:42:17,390 --> 00:42:19,520 through collisions or some other process 666 00:42:19,530 --> 00:42:21,260 because that gives me some hope 667 00:42:21,260 --> 00:42:24,130 that it'll go on for a long, long time. 668 00:42:24,431 --> 00:42:27,931 I have spent hours for You, please spend 5 seconds for me Visit www.nicolascanni.com + click on the Ads - Thank You! 54613

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