1 00:00:03,269 --> 00:00:06,071 MIKE ROWE: Our universe is at war. 2 00:00:06,172 --> 00:00:10,976 The universe is a very violent and deadly place. 3 00:00:11,077 --> 00:00:14,146 ROWE: Entire galaxies fight to the death. 4 00:00:14,247 --> 00:00:16,582 OLUSEYI: Talk about clash of the Titans. 5 00:00:16,683 --> 00:00:19,151 It doesn't get more titanic than this. 6 00:00:19,252 --> 00:00:21,153 It's a slaughter. It's a massacre. 7 00:00:21,254 --> 00:00:23,789 ROWE: Only the strongest survive. 8 00:00:23,890 --> 00:00:25,591 If a galaxy wants to stay alive, 9 00:00:25,692 --> 00:00:28,594 it has to feed on other galaxies. 10 00:00:28,695 --> 00:00:32,064 ROWE: Our own galaxy also fights for survival. 11 00:00:33,066 --> 00:00:36,602 We are facing the ultimate destruction 12 00:00:36,703 --> 00:00:38,971 of the Milky Way Galaxy. 13 00:00:39,072 --> 00:00:42,474 ROWE: These battles are how galaxies live, 14 00:00:42,575 --> 00:00:44,943 grow, and die. 15 00:00:45,045 --> 00:00:48,013 These collisions got us to where we are today, 16 00:00:48,114 --> 00:00:50,549 and they're going to determine the future of the universe. 17 00:00:50,650 --> 00:00:55,254 ♪♪ 18 00:00:55,355 --> 00:01:03,355 ♪♪ 19 00:01:04,631 --> 00:01:07,399 In 2018, astronomers used the Gaia 20 00:01:07,500 --> 00:01:10,836 space telescope to map our Milky Way Galaxy. 21 00:01:12,672 --> 00:01:16,075 They tracked the movements of a billion stars, 22 00:01:16,176 --> 00:01:19,845 and they found that some behave very strangely. 23 00:01:21,381 --> 00:01:24,450 When astronomers were mapping stars in our galaxy, 24 00:01:24,551 --> 00:01:27,286 they found a whole bunch that we're on similar 25 00:01:27,387 --> 00:01:29,288 but very strange orbits. 26 00:01:29,389 --> 00:01:31,824 Most stars of the Milky Way are orbiting in a sort of 27 00:01:31,925 --> 00:01:34,126 regular pattern, but these stars 28 00:01:34,260 --> 00:01:37,496 at the center, they're in these highly elongated orbits. 29 00:01:37,597 --> 00:01:39,531 Coming in from very far, 30 00:01:39,632 --> 00:01:43,068 swinging around the center of our galaxy, and then going back 31 00:01:43,169 --> 00:01:46,672 out again, a little bit like a comet does. 32 00:01:46,773 --> 00:01:48,407 ROWE: This group of stars plunges 33 00:01:48,508 --> 00:01:51,844 wildly through the center of our galaxy. 34 00:01:51,945 --> 00:01:55,214 When you track their direction and speed on a chart, 35 00:01:55,315 --> 00:01:58,951 you get a shape that looks a bit like a sausage. 36 00:02:01,421 --> 00:02:02,788 This doesn't sound very science-y, 37 00:02:02,922 --> 00:02:05,858 but this sausage is really what the stars look like 38 00:02:05,959 --> 00:02:06,892 if you look at the shapes 39 00:02:06,993 --> 00:02:09,128 of their orbits in a certain configuration. 40 00:02:10,730 --> 00:02:14,600 ROWE: What sent so many stars on such a strange path? 41 00:02:14,701 --> 00:02:17,769 It must have been a huge event. 42 00:02:18,872 --> 00:02:21,707 We think these stars are the result of a past 43 00:02:21,808 --> 00:02:22,908 cosmic collision. 44 00:02:25,245 --> 00:02:28,180 ROWE: They are casualties from an enormous battle between 45 00:02:28,281 --> 00:02:31,817 the Milky Way and a foreign galactic army. 46 00:02:34,988 --> 00:02:36,855 BULLOCK: They don't move like stars in the Milky Way, 47 00:02:36,956 --> 00:02:39,191 because they're not from the Milky Way. 48 00:02:39,292 --> 00:02:41,793 These stars are actually alien stars. 49 00:02:41,895 --> 00:02:44,363 They're invaders from outer, outer space. 50 00:02:46,299 --> 00:02:49,168 ROWE: The attackers left their mark on the Milky Way. 51 00:02:50,370 --> 00:02:53,705 We find similar battle scars on galaxies across 52 00:02:53,806 --> 00:02:55,841 the universe. 53 00:02:55,942 --> 00:02:57,709 Our models of galaxy information are still 54 00:02:57,810 --> 00:02:58,911 pretty uncertain. 55 00:02:59,012 --> 00:03:01,947 We still don't really understand how galaxies got to 56 00:03:02,048 --> 00:03:05,217 where they are, how we go from the Big Bang to the Milky Way. 57 00:03:06,719 --> 00:03:10,722 ROWE: Wars between galaxies have profound consequences, for 58 00:03:10,823 --> 00:03:14,059 the winners, the losers, and for us. 59 00:03:14,160 --> 00:03:18,430 What we're learning is that these galactic battles have had 60 00:03:18,531 --> 00:03:22,100 a huge impact on what the universe looks like today. 61 00:03:22,202 --> 00:03:24,002 THALLER: Our understanding of galaxies has changed 62 00:03:24,103 --> 00:03:25,837 entirely in the last few decades. 63 00:03:25,939 --> 00:03:28,607 We understand now that every big galaxy like the Milky Way 64 00:03:28,708 --> 00:03:31,143 started from many smaller things colliding, 65 00:03:31,244 --> 00:03:32,811 changing each other as they went. 66 00:03:34,480 --> 00:03:36,348 ROWE: Nearly 10 billion years ago, 67 00:03:36,449 --> 00:03:39,718 the sausage stars were part of a foreign galaxy. 68 00:03:41,688 --> 00:03:45,557 It was on a collision course with our home, the Milky Way. 69 00:03:47,093 --> 00:03:51,230 We call this invading army the Sausage Galaxy, 70 00:03:51,331 --> 00:03:53,865 or Gaia-Enceladus. 71 00:03:53,967 --> 00:03:56,702 PLAIT: The galaxy that we fought probably had 72 00:03:56,803 --> 00:03:58,437 about 50 billion stars, 73 00:03:58,538 --> 00:04:00,706 so we're talking about something that is a significant 74 00:04:00,807 --> 00:04:02,841 fraction of the size of the Milky Way. 75 00:04:05,511 --> 00:04:08,013 ROWE: Gaia-Enceladus was a tough opponent, 76 00:04:09,716 --> 00:04:14,119 but the Milky Way was 20 times its mass, 77 00:04:14,220 --> 00:04:16,588 and that makes a huge difference. 78 00:04:16,689 --> 00:04:19,625 When galaxies interact with each other, 79 00:04:19,726 --> 00:04:21,393 size definitely matters. 80 00:04:21,494 --> 00:04:24,963 The bigger galaxies are gonna dominate over the smaller ones, 81 00:04:25,064 --> 00:04:28,700 ripping them apart and essentially consuming them. 82 00:04:28,801 --> 00:04:32,204 Galaxy interactions are all about bullies. 83 00:04:32,305 --> 00:04:35,107 The bigger you are, the badder you are. 84 00:04:35,208 --> 00:04:37,242 SUTTER: When two galaxies collide, 85 00:04:37,343 --> 00:04:42,648 it's like two massive armies marching towards each other. 86 00:04:42,749 --> 00:04:45,384 These galaxies aren't fighting 87 00:04:45,485 --> 00:04:50,088 with knives or spears or guns or even nuclear bombs. 88 00:04:50,189 --> 00:04:51,256 They're fighting with something 89 00:04:51,357 --> 00:04:54,693 much more powerful -- Gravity itself. 90 00:04:56,296 --> 00:05:00,632 ROWE: Each galaxy contains billions of stars and planets 91 00:05:00,733 --> 00:05:03,302 and a supermassive black hole, 92 00:05:03,403 --> 00:05:06,405 millions of times the mass of the sun. 93 00:05:06,506 --> 00:05:09,441 That's a lot of gravitational firepower. 94 00:05:11,010 --> 00:05:13,445 SUTTER: As these galaxies approach each other, 95 00:05:13,546 --> 00:05:17,616 you can get tidal effects -- The same way that the moon can 96 00:05:17,717 --> 00:05:21,420 raise tides on one side of the Earth and the opposite side, 97 00:05:21,521 --> 00:05:25,190 one galaxy can stretch another 98 00:05:25,291 --> 00:05:27,926 galaxy along a certain direction. 99 00:05:32,632 --> 00:05:35,801 ROWE: As Gaia-Enceladus advanced towards us, 100 00:05:35,902 --> 00:05:38,537 our galaxy's superior gravity grabbed 101 00:05:38,638 --> 00:05:40,505 hold of the smaller galaxy. 102 00:05:41,974 --> 00:05:44,509 As it approached, the gravity from the Milky Way 103 00:05:44,610 --> 00:05:46,311 would have stretched it out. 104 00:05:47,680 --> 00:05:51,983 ROWE: Gaia-Enceladus was distorted but not defeated. 105 00:05:52,085 --> 00:05:54,820 The battle was just beginning. 106 00:05:54,921 --> 00:05:56,621 It would have passed through our galaxy, 107 00:05:56,723 --> 00:05:59,791 maybe orbiting a couple of times before being torn 108 00:05:59,892 --> 00:06:03,261 apart by our gravity. 109 00:06:04,964 --> 00:06:07,165 ROWE: The Milky Way's gravitational power 110 00:06:07,266 --> 00:06:10,235 ripped Gaia-Enceladus apart 111 00:06:10,336 --> 00:06:12,838 and captured billions of its stars. 112 00:06:15,108 --> 00:06:17,175 Eventually, most of those stars would have 113 00:06:17,276 --> 00:06:18,710 then settled down into 114 00:06:18,811 --> 00:06:21,780 the disk of the Milky Way and become a part of it. 115 00:06:21,881 --> 00:06:24,216 Little galaxy try to take on the Milky Way -- 116 00:06:24,317 --> 00:06:25,617 You're gonna get what's coming to you. 117 00:06:27,019 --> 00:06:28,620 ROWE: Despite winning the battle, 118 00:06:28,721 --> 00:06:31,990 the Milky Way suffered serious damage. 119 00:06:33,559 --> 00:06:35,293 The collision with the Sausage Galaxy 120 00:06:35,395 --> 00:06:37,229 left a scar on the Milky Way. 121 00:06:37,363 --> 00:06:39,297 And when we look near the center of our galaxy, 122 00:06:39,365 --> 00:06:43,935 we see a bulge that's left over from that collision. 123 00:06:44,036 --> 00:06:48,006 ROWE: The Milky Way isn't the only galaxy scarred by war. 124 00:06:49,776 --> 00:06:51,009 Across the universe, 125 00:06:51,110 --> 00:06:57,182 rival armies made up of billions of stars slug it out, 126 00:06:57,283 --> 00:07:02,254 leaving behind distorted and damaged casualties of war. 127 00:07:04,357 --> 00:07:05,424 HOPKINS: There's a million different 128 00:07:05,525 --> 00:07:06,925 sub-categories of them. 129 00:07:07,026 --> 00:07:09,594 There's tadpole galaxies that have long tails, 130 00:07:09,695 --> 00:07:11,430 longer than our own galaxy. 131 00:07:11,531 --> 00:07:14,366 There are things like Arp-Madore 2026, where you see 132 00:07:14,467 --> 00:07:16,034 this eerie, glowing face, 133 00:07:16,135 --> 00:07:19,905 two big eyes looking right at you from across the universe. 134 00:07:20,006 --> 00:07:22,174 There are galaxies that looked like they might have collided 135 00:07:22,275 --> 00:07:24,843 with one another and blown holes through each other. 136 00:07:28,014 --> 00:07:30,649 ROWE: These battle scars give us important clues 137 00:07:30,750 --> 00:07:34,419 about one of the biggest mysteries in astronomy -- 138 00:07:34,520 --> 00:07:36,955 How galaxies develop and grow. 139 00:07:38,391 --> 00:07:40,525 But there's a problem. 140 00:07:40,626 --> 00:07:44,496 We can't watch these battles in real time. 141 00:07:44,597 --> 00:07:47,232 The scale of galaxies is huge. 142 00:07:47,333 --> 00:07:49,267 They're hundreds of thousands of light years across. 143 00:07:49,368 --> 00:07:50,569 It's going to take them millions 144 00:07:50,670 --> 00:07:52,571 or billions of years to come together. 145 00:07:53,873 --> 00:07:56,208 So it's like looking at one frame 146 00:07:56,309 --> 00:07:58,610 from a really energetic fight scene in a movie. 147 00:08:00,179 --> 00:08:02,247 ROWE: By piecing these snapshots together, 148 00:08:02,348 --> 00:08:06,318 astronomers can build up a detailed picture of past 149 00:08:06,419 --> 00:08:10,522 conflicts and discover how these battles transformed 150 00:08:10,623 --> 00:08:13,625 galaxies over billions of years. 151 00:08:13,726 --> 00:08:16,361 We have pictures of isolated galaxies, 152 00:08:16,462 --> 00:08:18,363 we have pictures of interacting galaxies, 153 00:08:18,464 --> 00:08:21,132 and we have pictures of aftermath galaxies. 154 00:08:22,502 --> 00:08:26,204 ROWE: And that's helped us discover something alarming. 155 00:08:26,305 --> 00:08:30,342 The Milky Way faces yet another attack from 156 00:08:30,443 --> 00:08:34,913 an enemy armed with an enormous secret weapon. 157 00:08:35,014 --> 00:08:38,316 Will our solar system survive the onslaught? 158 00:08:50,129 --> 00:08:51,596 ROWE: Across the universe, 159 00:08:51,697 --> 00:08:53,598 galaxies are at war, 160 00:08:55,768 --> 00:08:57,469 Their main weapon -- 161 00:08:57,570 --> 00:08:59,037 Gravity. 162 00:08:59,138 --> 00:09:03,575 It tears the combatants into weird and wonderful shapes. 163 00:09:03,676 --> 00:09:07,646 Our galaxy didn't escape the mayhem. 164 00:09:07,747 --> 00:09:10,048 It's peppered with battle scars. 165 00:09:12,351 --> 00:09:13,718 The overall shape of the Milky Way 166 00:09:13,819 --> 00:09:16,454 is a flat disk of stars and gas. 167 00:09:16,556 --> 00:09:20,091 Except recently, we have found out that at the edges, 168 00:09:20,192 --> 00:09:23,461 it's actually warped a little bit like the brim of a fedora. 169 00:09:23,563 --> 00:09:26,298 The stars actually dip down below the plane on 170 00:09:26,365 --> 00:09:29,801 one side and dip above it on the other. 171 00:09:29,902 --> 00:09:32,571 ROWE: We think the attacker was one of our satellites, 172 00:09:32,672 --> 00:09:36,474 a galaxy that orbits the Milky Way like the moon 173 00:09:36,576 --> 00:09:38,009 orbits the Earth. 174 00:09:38,110 --> 00:09:42,213 It's called the Sagittarius Dwarf Galaxy. 175 00:09:42,315 --> 00:09:45,183 From looking at how the stars move in the Milky Way, 176 00:09:45,284 --> 00:09:48,620 we suspect that the Sagittarius Dwarf Galaxy has 177 00:09:48,721 --> 00:09:51,990 actually crashed through the Milky Way a few times on 178 00:09:52,091 --> 00:09:54,526 its course of its orbit around the galaxy. 179 00:09:54,627 --> 00:09:56,428 BULLOCK: It came in about six billion years ago, 180 00:09:56,529 --> 00:09:59,331 hit the disk hard about two billion years ago, and crashed 181 00:09:59,432 --> 00:10:01,566 again about a billion years ago. 182 00:10:01,667 --> 00:10:04,603 PLAIT: And our gravity has pulled it out into a gigantic, 183 00:10:04,704 --> 00:10:07,505 looping stream of stars that is moving in and out 184 00:10:07,607 --> 00:10:09,307 of our Milky Way. 185 00:10:11,377 --> 00:10:13,178 ROWE: The war is not over. 186 00:10:13,279 --> 00:10:16,681 The insurgent galaxy will return. 187 00:10:16,782 --> 00:10:19,684 When galaxies interact, 188 00:10:19,785 --> 00:10:22,454 often they're caught in this huge cosmic dance 189 00:10:22,555 --> 00:10:24,990 where they revolve around each other a few times, 190 00:10:25,091 --> 00:10:27,459 or they even crash through each other and then come 191 00:10:27,560 --> 00:10:28,493 back around. 192 00:10:28,594 --> 00:10:30,595 The Sagittarius Dwarf Galaxy looks like 193 00:10:30,696 --> 00:10:34,366 it's crashing in with ever increasing frequency. 194 00:10:34,467 --> 00:10:37,569 ROWE: A new skirmish could take place in the next 195 00:10:37,670 --> 00:10:40,038 100 million years. 196 00:10:40,139 --> 00:10:44,042 So should we be worried about these attacks? 197 00:10:44,143 --> 00:10:46,978 SUTTER: Because the Sagittarius Dwarf Galaxy is so small 198 00:10:47,079 --> 00:10:48,446 compared to the Milky Way, 199 00:10:48,547 --> 00:10:50,482 it will do some damage at the beginning, 200 00:10:50,583 --> 00:10:54,552 but because we're so massive, we can absorb the impact. 201 00:10:54,654 --> 00:10:56,955 I mean, this galaxy, it's looking for a fight, 202 00:10:57,056 --> 00:11:00,458 but it's also 10,000 times smaller than us. 203 00:11:00,559 --> 00:11:02,627 So this is gonna be no sweat at all. 204 00:11:06,232 --> 00:11:09,334 ROWE: So far, the Milky Way has been victorious. 205 00:11:10,770 --> 00:11:12,804 But the danger isn't over. 206 00:11:14,373 --> 00:11:17,275 We are surrounded by enemies. 207 00:11:17,376 --> 00:11:19,244 SUTTER: Our local neighborhood of galaxies 208 00:11:19,345 --> 00:11:21,546 has three major galaxies, 209 00:11:21,647 --> 00:11:24,582 but up to 50 smaller ones. 210 00:11:24,684 --> 00:11:28,420 All these galaxies are potential troublemakers. 211 00:11:28,521 --> 00:11:32,123 Each one of these could be armies that rise up against us. 212 00:11:33,793 --> 00:11:36,261 The two most famous galaxies that orbit 213 00:11:36,362 --> 00:11:39,864 the Milky Way are the Large and Small Magellanic Clouds. 214 00:11:39,965 --> 00:11:43,368 These are two independent dwarf galaxies that you can 215 00:11:43,469 --> 00:11:45,970 see in the night sky from the Southern Hemisphere. 216 00:11:50,042 --> 00:11:53,311 ROWE: We thought the Large Magellanic Cloud orbited 217 00:11:53,412 --> 00:11:58,483 our galaxy at a safe distance of 160,000 light years. 218 00:11:59,719 --> 00:12:01,152 We thought it would stay that way, 219 00:12:01,253 --> 00:12:04,022 and we thought it was harmless. 220 00:12:04,123 --> 00:12:09,094 Now, a new discovery shows we were wrong on all counts. 221 00:12:10,529 --> 00:12:14,265 The new factor that changed our view of the Magellanic Cloud 222 00:12:14,366 --> 00:12:15,333 is we found out 223 00:12:15,434 --> 00:12:18,103 it has a lot more dark matter than we thought. 224 00:12:20,072 --> 00:12:21,673 ROWE: Dark matter, 225 00:12:21,774 --> 00:12:25,310 the most mysterious stuff in the universe. 226 00:12:25,411 --> 00:12:28,980 A dark matter is literally what it sounds like. 227 00:12:29,081 --> 00:12:30,648 It's matter that we cannot see. 228 00:12:30,750 --> 00:12:32,884 But it has gravity and can affect objects 229 00:12:32,985 --> 00:12:34,285 that we can see. 230 00:12:37,590 --> 00:12:40,992 ROWE: Adding in this extra dark matter makes the Large 231 00:12:41,093 --> 00:12:45,697 Magellanic Cloud at least twice a massive as predicted. 232 00:12:45,798 --> 00:12:48,967 So its gravity is double what we thought. 233 00:12:50,536 --> 00:12:53,071 It's secretly been gathering 234 00:12:53,172 --> 00:12:57,442 allies, has been gathering dark matter on its side, 235 00:12:57,543 --> 00:13:00,845 and now it's a much bigger threat than we thought before. 236 00:13:02,414 --> 00:13:04,249 So it's not just going to orbit us. 237 00:13:04,350 --> 00:13:06,050 It's gonna collide with the Milky Way. 238 00:13:07,720 --> 00:13:10,522 ROWE: Moving at nearly a million miles an hour, 239 00:13:10,623 --> 00:13:15,226 the Large Magellanic Cloud will not swing past us. 240 00:13:15,327 --> 00:13:17,529 It will attack. 241 00:13:17,630 --> 00:13:19,998 The large Magellanic Cloud is 242 00:13:20,099 --> 00:13:23,368 1/10 the mass of the Milky Way. 243 00:13:23,469 --> 00:13:26,304 That's enough to make a pretty big punch. 244 00:13:28,107 --> 00:13:30,074 ROWE: In about 2.5 billion years, 245 00:13:30,176 --> 00:13:32,777 it will smash into our galaxy. 246 00:13:36,081 --> 00:13:39,217 SUTTER: It's gonna plow through the disk of the Milky Way, 247 00:13:39,318 --> 00:13:40,819 it's gonna blow a cavity. 248 00:13:40,920 --> 00:13:43,621 It might even damage our spiral arms. 249 00:13:45,991 --> 00:13:49,327 ROWE: Earth sits in one of those spiral arms. 250 00:13:51,597 --> 00:13:54,365 Could our planet become collateral damage? 251 00:13:55,835 --> 00:13:58,436 If the Large Magellanic Cloud passes through the plane 252 00:13:58,537 --> 00:14:01,239 of our galaxy near our location, 253 00:14:01,340 --> 00:14:03,308 that can have dire consequences. 254 00:14:05,010 --> 00:14:07,078 ROWE: The gravitational clash between 255 00:14:07,179 --> 00:14:09,147 the invader on the Milky Way 256 00:14:09,248 --> 00:14:12,350 could hurl stars and planets out of our galaxy. 257 00:14:14,220 --> 00:14:16,087 Earth could be one of them. 258 00:14:17,723 --> 00:14:20,525 HOPKINS: Our planet's very close to its own star, 259 00:14:20,626 --> 00:14:23,828 so the odds are that you'll just get ripped out 260 00:14:23,929 --> 00:14:25,096 along with your star, 261 00:14:25,197 --> 00:14:28,132 so we'd be moving along with the sun even as the sun gets 262 00:14:28,234 --> 00:14:30,869 jettisoned from our galaxy. 263 00:14:30,970 --> 00:14:33,705 PLAIT: And it'll move off out into intergalactic space. 264 00:14:33,806 --> 00:14:35,506 And that's not terrible. 265 00:14:35,608 --> 00:14:37,375 I mean, it's not gonna get destroyed, 266 00:14:37,476 --> 00:14:38,710 but it's a little lonely. 267 00:14:42,014 --> 00:14:44,482 ROWE: Our view of the night sky 268 00:14:44,583 --> 00:14:45,984 would radically change. 269 00:14:47,586 --> 00:14:50,455 OLUSEYI: We'd be able to see much more of the Milky Way, 270 00:14:50,556 --> 00:14:54,225 especially if we got kicked up above the plane of the galaxy. 271 00:14:54,326 --> 00:14:56,794 We'd be able to see the whole shebang. 272 00:14:56,896 --> 00:15:00,531 Just look at any image of a spiral galaxy. 273 00:15:00,633 --> 00:15:03,768 They're gorgeous. Now imagine seeing your night 274 00:15:03,869 --> 00:15:07,338 sky filled with a face-on spiral galaxy. 275 00:15:07,439 --> 00:15:09,908 [scoffs] That would be like waking up to my face 276 00:15:10,009 --> 00:15:12,810 every morning -- spectacular. 277 00:15:12,912 --> 00:15:15,546 [laughs] 278 00:15:17,449 --> 00:15:19,951 ROWE: If we were unlucky, 279 00:15:20,052 --> 00:15:21,619 our home planet could have 280 00:15:21,720 --> 00:15:25,023 a close encounter with an invading star. 281 00:15:25,124 --> 00:15:28,927 PLAIT: The odds are very low that another star 282 00:15:29,028 --> 00:15:30,728 will pass close by the sun, 283 00:15:30,829 --> 00:15:32,764 but those odds aren't zero. 284 00:15:32,865 --> 00:15:34,565 It could happen that another star 285 00:15:34,667 --> 00:15:36,734 passes close enough to affect the planets. 286 00:15:36,835 --> 00:15:38,503 And if that were to happen, 287 00:15:38,604 --> 00:15:43,541 it could upset the delicate balance in the solar system. 288 00:15:44,576 --> 00:15:47,779 OLUSEYI: We don't know where the Earth could end up. 289 00:15:47,880 --> 00:15:49,847 It might find its way into the sun. 290 00:15:49,949 --> 00:15:50,982 You just don't know. 291 00:15:51,083 --> 00:15:52,850 Or there might just be a rain 292 00:15:52,952 --> 00:15:55,386 of comets into our inner solar system. 293 00:15:55,487 --> 00:15:57,922 MINGARELLI: Our own planet might be flung out, 294 00:15:58,023 --> 00:16:01,225 in which case, this would be a death knell for all life 295 00:16:01,327 --> 00:16:02,560 on Earth. 296 00:16:02,661 --> 00:16:05,263 I'm not someone who is like a doom and gloom person, 297 00:16:05,364 --> 00:16:07,165 but, like, that would be insane. 298 00:16:08,500 --> 00:16:10,068 OLUSEYI: You don't know what's gonna happen, 299 00:16:10,169 --> 00:16:13,338 but most of the options are bad. 300 00:16:13,439 --> 00:16:16,641 ROWE: All these nightmare scenarios 301 00:16:16,742 --> 00:16:18,476 will extinguish life. 302 00:16:22,114 --> 00:16:24,983 Earth might survive, but our cosmic 303 00:16:25,084 --> 00:16:27,618 zip code will take a severe beating. 304 00:16:29,221 --> 00:16:31,422 SUTTER: The Milky Way Galaxy is bigger than 305 00:16:31,523 --> 00:16:32,623 the Large Magellanic Cloud, 306 00:16:32,691 --> 00:16:35,426 so we are gonna win, [exhales heavily] 307 00:16:35,527 --> 00:16:37,328 but it's gonna hurt us for a long time. 308 00:16:39,031 --> 00:16:40,598 ROWE: The Large Magellanic Cloud 309 00:16:40,699 --> 00:16:42,667 will leave our galaxy battered, 310 00:16:42,768 --> 00:16:45,737 bruised, but ultimately undefeated. 311 00:16:45,838 --> 00:16:49,741 But there's a far bigger threat looming 312 00:16:49,842 --> 00:16:51,576 over the Milky Way. 313 00:16:51,677 --> 00:16:54,612 It's gonna face an opponent that it can't defeat. 314 00:16:55,981 --> 00:16:58,182 ROWE: Will this mega collision be 315 00:16:58,283 --> 00:17:00,585 the Milky Way's last stand? 316 00:17:11,630 --> 00:17:13,131 ROWE: For billions of years, 317 00:17:13,232 --> 00:17:16,234 the Milky Way conquered galaxy after galaxy, 318 00:17:16,335 --> 00:17:19,837 tearing its smaller rivals to pieces. 319 00:17:21,106 --> 00:17:24,075 But our galaxy is about to meet its match. 320 00:17:27,112 --> 00:17:31,082 In the not-too-distant future, galactically speaking, 321 00:17:31,183 --> 00:17:34,819 a much, much larger battle is due for the Milky Way. 322 00:17:36,522 --> 00:17:38,923 ROWE: A battle with a local superpower, 323 00:17:40,225 --> 00:17:41,526 the Andromeda Galaxy. 324 00:17:43,095 --> 00:17:46,731 We thought this huge galaxy might wound us in the future. 325 00:17:48,167 --> 00:17:51,702 Now, recent evidence reveals it's going to make 326 00:17:51,804 --> 00:17:54,472 a full-scale assault. 327 00:17:54,573 --> 00:17:58,109 We've known for a long time that Andromeda is heading 328 00:17:58,210 --> 00:18:00,378 more or less toward us, 329 00:18:00,479 --> 00:18:02,847 but we didn't know exactly in what direction. 330 00:18:02,948 --> 00:18:04,549 But in recent years, we've been 331 00:18:04,650 --> 00:18:06,651 able to pinpoint this a lot better. 332 00:18:06,752 --> 00:18:10,354 And, uh, yeah, it's -- It's heading right for us. 333 00:18:13,092 --> 00:18:16,160 ROWE: Data from the Hubble Space Telescope shows 334 00:18:16,261 --> 00:18:20,164 two galaxies will collide in about four billion years, 335 00:18:23,001 --> 00:18:26,871 and it will be a monumental battle. 336 00:18:26,972 --> 00:18:30,875 This collision that is coming, and it is coming, is not gonna 337 00:18:30,976 --> 00:18:33,411 be anything like the Milky Way has experienced before 338 00:18:33,512 --> 00:18:35,613 in its 10- or 12-billion-year history. 339 00:18:35,714 --> 00:18:38,316 This is a galaxy of comparable size. 340 00:18:38,417 --> 00:18:42,720 This is two heavyweight prize fighters coming at it. 341 00:18:42,821 --> 00:18:46,924 ROWE: Warriors with the same gravitational firepower. 342 00:18:47,025 --> 00:18:50,795 Simulations suggest a clash of the Titans. 343 00:18:50,896 --> 00:18:53,331 BASRI: Each of them with half a trillion stars in them. 344 00:18:53,432 --> 00:18:55,900 That sounds like a pretty spectacular collision. 345 00:18:57,970 --> 00:19:00,905 ROWE: Fights between equally matched galaxies 346 00:19:01,006 --> 00:19:03,508 are rare and messy. 347 00:19:03,609 --> 00:19:05,576 When the battle kicks off, 348 00:19:05,677 --> 00:19:08,579 there will be no good news for either side. 349 00:19:10,749 --> 00:19:13,384 PLAIT: When the Andromeda Galaxy and the Milky Way Galaxy 350 00:19:13,485 --> 00:19:14,852 start to get close, 351 00:19:14,953 --> 00:19:16,521 they're gonna start affecting each 352 00:19:16,622 --> 00:19:17,688 other profoundly. 353 00:19:17,789 --> 00:19:20,057 Tendrils of stars are gonna be thrown out. 354 00:19:20,159 --> 00:19:23,961 Gas is gonna be thrown out. 355 00:19:24,062 --> 00:19:26,564 ROWE: It won't be a single impact. 356 00:19:26,665 --> 00:19:29,600 Gravity will send the two opponents 357 00:19:29,701 --> 00:19:32,436 into a spiraling dance of death. 358 00:19:34,606 --> 00:19:36,874 PLAIT: The first pass is actually not a direct hit. 359 00:19:36,975 --> 00:19:39,677 They're gonna swing past each other, in fact. 360 00:19:39,778 --> 00:19:42,180 And at this point, their gravitational 361 00:19:42,281 --> 00:19:43,781 interaction is gonna slow them down, 362 00:19:43,882 --> 00:19:46,017 and they're gonna come back toward each other. 363 00:19:46,118 --> 00:19:49,654 ROWE: The galaxies will collide and fly apart again, 364 00:19:49,755 --> 00:19:54,292 inflicting more and more damage with each clash. 365 00:19:54,393 --> 00:19:56,928 If you were to go outside and look up, 366 00:19:57,029 --> 00:20:00,031 you could see the disk of our galaxy getting ripped apart 367 00:20:00,132 --> 00:20:02,300 by tidal interactions with Andromeda. 368 00:20:05,971 --> 00:20:09,307 ROWE: The two beautiful spiral galaxies 369 00:20:09,408 --> 00:20:11,709 will tear each other apart, 370 00:20:11,810 --> 00:20:16,347 leaving one vast elliptical galaxy. 371 00:20:18,283 --> 00:20:21,352 PLAIT: The fate of the Andromeda, Milky Way 372 00:20:21,453 --> 00:20:24,689 battle is that they will merge. 373 00:20:24,790 --> 00:20:28,392 This is going to be one gigantic galaxy. 374 00:20:31,463 --> 00:20:32,730 OLUSEYI: And that presents a problem. 375 00:20:32,831 --> 00:20:34,498 What are we gonna call this new galaxy? 376 00:20:34,600 --> 00:20:37,568 Of course, my nerd colleagues have come up with 377 00:20:37,669 --> 00:20:40,504 names like Milkomeda, Andromeway. 378 00:20:40,606 --> 00:20:42,740 Whatever, those are corny. 379 00:20:42,841 --> 00:20:44,875 We should just call it Hakeem. 380 00:20:50,949 --> 00:20:53,484 ROWE: With a trillion stars, it will be 381 00:20:53,585 --> 00:20:56,420 one of the biggest galaxies in the universe. 382 00:20:58,957 --> 00:21:00,124 OLUSEYI: In the Hakeem Galaxy, 383 00:21:00,225 --> 00:21:02,260 things gonna be completely new. 384 00:21:02,361 --> 00:21:05,663 First off, it's gonna be a really good-looking galaxy. 385 00:21:05,764 --> 00:21:07,498 Let's get that straight from the get-go. 386 00:21:07,599 --> 00:21:12,637 Second, it's gonna be powerful, and I'm talking powerful. 387 00:21:12,738 --> 00:21:14,372 This may be the most remarkable 388 00:21:14,473 --> 00:21:16,574 galaxy in the history of the universe. 389 00:21:19,111 --> 00:21:23,080 ROWE: Milkomeda, or Hakeem, if you prefer, 390 00:21:23,181 --> 00:21:26,550 will become the undisputed boss of our cosmic neighborhood. 391 00:21:26,618 --> 00:21:30,121 It's calm appearance concealing 392 00:21:30,222 --> 00:21:31,789 a history of violence. 393 00:21:34,826 --> 00:21:37,962 It's the result of a complete war zone of mergers over 394 00:21:38,063 --> 00:21:39,230 the course of billions of years, 395 00:21:39,331 --> 00:21:42,333 many galaxies crashing together, fully reconfiguring 396 00:21:42,434 --> 00:21:44,502 each time and slowly, you grow 397 00:21:44,603 --> 00:21:48,172 this smooth, placid, big blob of stars. 398 00:21:50,242 --> 00:21:53,077 ROWE: After billions of years of warfare, 399 00:21:53,178 --> 00:21:56,147 our galaxy will finally be peaceful. 400 00:21:58,750 --> 00:22:02,586 But before it's honorable discharge, Milkomeda 401 00:22:02,688 --> 00:22:04,755 may produce one final, 402 00:22:04,856 --> 00:22:07,625 devastating act of war. 403 00:22:07,726 --> 00:22:11,896 Imagine World War II, and then all of a sudden, 404 00:22:11,997 --> 00:22:14,865 one of the sides comes up with the Death Star. 405 00:22:14,966 --> 00:22:16,500 That's what we're talking about here. 406 00:22:19,071 --> 00:22:21,405 ROWE: A weapon of cosmic destruction. 407 00:22:21,506 --> 00:22:28,179 ♪♪ 408 00:22:37,789 --> 00:22:40,024 ROWE: When giant galaxies clash, 409 00:22:40,125 --> 00:22:43,094 the battles are spectacular and destructive. 410 00:22:46,264 --> 00:22:50,401 The victors steal huge numbers of stars and vast amounts 411 00:22:50,502 --> 00:22:55,272 of gas as fuel for the ultimate super weapon. 412 00:22:57,342 --> 00:23:00,211 The special weapon that these monster galaxies 413 00:23:00,312 --> 00:23:03,447 have is a giant Death Ray, 414 00:23:03,548 --> 00:23:08,419 a jet of material racing across thousands of light-years. 415 00:23:10,822 --> 00:23:13,524 ROWE: These huge outbursts of energy blast out 416 00:23:13,625 --> 00:23:16,694 of the center of the colliding galaxies. 417 00:23:16,795 --> 00:23:20,030 They produce more energy in one second than 418 00:23:20,132 --> 00:23:25,169 the sun will in its entire 10-billion-year lifetime. 419 00:23:25,270 --> 00:23:27,204 We call them jets. 420 00:23:28,974 --> 00:23:33,144 These incredibly powerful jets aren't just brief features. 421 00:23:33,245 --> 00:23:36,380 They can be sustained for millions of years, 422 00:23:36,481 --> 00:23:38,549 and they can maintain their structure 423 00:23:38,650 --> 00:23:41,485 for thousands of light-years. 424 00:23:41,586 --> 00:23:43,454 It's like turning on a garden hose 425 00:23:43,555 --> 00:23:45,856 in Chicago and using it to water 426 00:23:45,957 --> 00:23:47,591 a garden in London. 427 00:23:49,561 --> 00:23:52,563 ROWE: Exactly what triggered these jets was a mystery. 428 00:23:52,664 --> 00:23:57,101 Then, in June 2018, astronomers in Hawaii captured 429 00:23:57,202 --> 00:24:00,337 something stunning -- A jet forming 430 00:24:00,439 --> 00:24:02,840 during a galactic collision. 431 00:24:05,410 --> 00:24:07,578 The team found something really incredible. 432 00:24:07,679 --> 00:24:11,015 They found two galaxies that were in a cosmic collision 433 00:24:11,116 --> 00:24:14,318 and actually found an active jet in one of these galaxies. 434 00:24:14,419 --> 00:24:16,754 It was the first time anything like this has been discovered. 435 00:24:20,325 --> 00:24:23,961 ROWE: When galaxies collide, the clash drives huge clouds 436 00:24:24,062 --> 00:24:27,465 of gas and dust towards their centers. 437 00:24:27,566 --> 00:24:31,168 The supermassive black holes start to feed. 438 00:24:33,371 --> 00:24:35,573 The gas that was in those galaxies starts to 439 00:24:35,674 --> 00:24:39,376 funnel toward the black hole and then fall upon it. 440 00:24:39,478 --> 00:24:42,012 ROWE: Not all this gas ends up inside 441 00:24:42,113 --> 00:24:44,148 the supermassive black hole. 442 00:24:44,249 --> 00:24:46,650 Powerful magnetic fields carry some of 443 00:24:46,751 --> 00:24:49,487 this matter to the poles 444 00:24:49,588 --> 00:24:52,723 and blast it out in tight, narrow jets. 445 00:24:52,824 --> 00:24:55,759 A super weapon is born. 446 00:24:55,861 --> 00:24:57,761 This discovery helps us understand 447 00:24:57,863 --> 00:25:01,832 how giant elliptical galaxies form. 448 00:25:01,933 --> 00:25:05,503 Knowing that mergers of spiral galaxies can cause 449 00:25:05,637 --> 00:25:07,204 these jets helps us put together 450 00:25:07,305 --> 00:25:09,807 a complete picture of how these huge elliptical 451 00:25:09,908 --> 00:25:11,408 galaxies might be formed. 452 00:25:14,412 --> 00:25:18,215 ROWE: The discovery doesn't answer all our questions. 453 00:25:18,316 --> 00:25:19,617 There's another mystery. 454 00:25:19,718 --> 00:25:21,952 How did the super giant galaxies that 455 00:25:22,053 --> 00:25:25,055 dwarf the Milky Way get so big? 456 00:25:25,156 --> 00:25:29,360 Our Milky Way Galaxy is big-ish. 457 00:25:29,461 --> 00:25:31,529 It's -- it's slightly bigger than average, 458 00:25:31,630 --> 00:25:33,864 but IC 1101, for example, 459 00:25:33,965 --> 00:25:37,635 is more than 50 times larger than our home galaxy and has 460 00:25:37,736 --> 00:25:42,006 more than a trillion, with a T, a trillion stars in it. 461 00:25:42,107 --> 00:25:47,177 The biggest galaxies make the Milky Way look like an ant. 462 00:25:47,279 --> 00:25:50,881 These galactic giants pose a problem. 463 00:25:50,982 --> 00:25:53,484 There hasn't been enough time since the birth of 464 00:25:53,585 --> 00:25:57,721 the universe for them to become so large, 465 00:25:57,822 --> 00:26:00,090 even by conquering smaller galaxies. 466 00:26:00,191 --> 00:26:03,227 When we look into the distant universe, 467 00:26:03,328 --> 00:26:06,530 we see something very strange that we don't quite understand. 468 00:26:06,631 --> 00:26:09,600 We see enormous galaxies that existed just 469 00:26:09,701 --> 00:26:11,502 a billion years after the Big Bang. 470 00:26:11,603 --> 00:26:14,638 And even though these cosmic collisions help explain how 471 00:26:14,739 --> 00:26:16,006 galaxies get bigger, 472 00:26:16,107 --> 00:26:18,943 they don't quite explain everything about how galaxies 473 00:26:19,044 --> 00:26:20,077 grow over time. 474 00:26:20,178 --> 00:26:22,346 So we still have a big mystery on our hands here. 475 00:26:26,217 --> 00:26:29,787 ROWE: So in 2019, an international team 476 00:26:29,888 --> 00:26:32,356 investigated a very large galaxy 477 00:26:32,457 --> 00:26:35,392 over 300 million light-years away. 478 00:26:35,493 --> 00:26:39,597 We call it NGC 6240. 479 00:26:39,698 --> 00:26:43,100 MINGARELLI: NGC 6240 was being studied because 480 00:26:43,201 --> 00:26:45,769 it had two supermassive black holes in it. 481 00:26:45,870 --> 00:26:48,071 Now the galaxy itself looked like it 482 00:26:48,139 --> 00:26:50,140 had been disturbed, like something had happened. 483 00:26:50,241 --> 00:26:53,711 They thought that potentially it had had a recent merger. 484 00:26:59,284 --> 00:27:01,251 ROWE: They were expecting to see two 485 00:27:01,353 --> 00:27:05,255 supermassive black holes in the galaxy's heart. 486 00:27:05,357 --> 00:27:08,258 As the researchers peered through the layers of gas 487 00:27:08,360 --> 00:27:12,429 and dust, they discovered something surprising. 488 00:27:12,530 --> 00:27:14,698 What we found was staggering. 489 00:27:14,799 --> 00:27:17,368 We found not two but three 490 00:27:17,469 --> 00:27:20,237 supermassive black holes lurking in the center. 491 00:27:26,611 --> 00:27:27,811 ROWE: It's the first time we found 492 00:27:27,912 --> 00:27:32,416 a galaxy with three supermassive black holes, 493 00:27:32,517 --> 00:27:35,986 evidence of a three-galaxy pile up. 494 00:27:36,087 --> 00:27:40,124 This galaxy is an active battlefield of 495 00:27:40,225 --> 00:27:46,096 not two but three armies colliding at once, 496 00:27:46,197 --> 00:27:47,931 and because there are three armies involved, 497 00:27:48,033 --> 00:27:50,167 there are three galaxies involved with 498 00:27:50,268 --> 00:27:53,504 three times as much mass, three times as many stars, 499 00:27:53,605 --> 00:27:56,206 three times as much material, and three times as 500 00:27:56,307 --> 00:27:58,475 much violence. 501 00:27:58,576 --> 00:28:01,445 ROWE: This three-way battle may explain how 502 00:28:01,546 --> 00:28:06,250 the largest galaxies got so big so fast. 503 00:28:06,351 --> 00:28:08,118 MINGARELLI: It could be that galaxy mergers 504 00:28:08,219 --> 00:28:11,121 are more frequent than what we thought previously, 505 00:28:11,222 --> 00:28:14,725 and therefore, galaxies become more massive 506 00:28:14,826 --> 00:28:16,860 faster than previously expected. 507 00:28:18,897 --> 00:28:21,031 ROWE: In the past, galaxies may have 508 00:28:21,132 --> 00:28:24,401 battled and collided more often than today. 509 00:28:24,502 --> 00:28:28,238 Back then, galaxies were more densely packed together. 510 00:28:29,808 --> 00:28:33,310 Our universe is expanding as it ages, which means in 511 00:28:33,411 --> 00:28:35,412 the past, all the galaxies in 512 00:28:35,513 --> 00:28:37,915 the universe were closer together, 513 00:28:38,016 --> 00:28:40,017 and that means they had greater chance for their 514 00:28:40,118 --> 00:28:41,618 gravitational interactions to 515 00:28:41,720 --> 00:28:43,921 pull them together and smash them together. 516 00:28:46,591 --> 00:28:49,593 ROWE: The early universe was at war. 517 00:28:49,694 --> 00:28:52,629 Conflicts between galaxies were common. 518 00:28:52,731 --> 00:28:56,200 They collided frequently and grew quickly. 519 00:28:57,769 --> 00:29:01,805 But not every galaxy profited from the carnage. 520 00:29:01,906 --> 00:29:04,675 Some brave galaxies took on the big guns 521 00:29:04,776 --> 00:29:06,744 and nearly died as a result. 522 00:29:21,526 --> 00:29:24,161 ROWE: When galaxies fight, the big get bigger. 523 00:29:24,262 --> 00:29:28,398 More mass means more gravity, the vital ingredient 524 00:29:28,500 --> 00:29:29,633 for victory. 525 00:29:31,803 --> 00:29:36,006 But galactic conflict doesn't always result in growth. 526 00:29:36,107 --> 00:29:39,777 A strange new astronomical object had 527 00:29:39,878 --> 00:29:41,245 scientists confused. 528 00:29:44,415 --> 00:29:46,717 MINGARELLI: They just looked like stars from the ground. 529 00:29:46,818 --> 00:29:50,154 However, with the advent of Hubble and beautiful 530 00:29:50,255 --> 00:29:51,955 space-based telescopes, 531 00:29:52,056 --> 00:29:56,059 it was possible to look at these stars again and actually 532 00:29:56,161 --> 00:29:58,028 discover that they were galaxies. 533 00:30:03,268 --> 00:30:04,635 HOPKINS: They're kind of crazy. 534 00:30:04,736 --> 00:30:09,807 They're a huge number of stars, but crammed into an incredibly 535 00:30:09,908 --> 00:30:12,009 tiny space on an astrophysical scale, 536 00:30:12,110 --> 00:30:16,446 something 500 times smaller than our Milky Way Galaxy. 537 00:30:16,548 --> 00:30:20,384 ROWE: We call them ultra-compact dwarf galaxies, 538 00:30:20,485 --> 00:30:21,819 or UCDs. 539 00:30:23,254 --> 00:30:25,756 HOPKINS: You might imagine the difference between 540 00:30:25,857 --> 00:30:29,960 the Milky Way Galaxy and a UCD as 541 00:30:30,061 --> 00:30:33,263 the difference between a cloud and a rock, 542 00:30:33,364 --> 00:30:36,700 where the rock is just the same kind of material, 543 00:30:36,801 --> 00:30:39,236 but compressed to just incredibly high densities 544 00:30:39,337 --> 00:30:41,572 compared to some fluffy gaseous thing. 545 00:30:44,576 --> 00:30:46,844 ROWE: What are these strange galaxies? 546 00:30:46,945 --> 00:30:49,546 They seem to break all the rules. 547 00:30:49,647 --> 00:30:52,983 To find out, astronomers zoomed in to 548 00:30:53,084 --> 00:30:54,685 a particularly dense, 549 00:30:54,786 --> 00:30:57,321 ultra-compact dwarf galaxy 550 00:30:57,422 --> 00:31:00,724 called M60-UCD1. 551 00:31:01,993 --> 00:31:05,963 M60-UCD1 is 300 light-years across. 552 00:31:06,064 --> 00:31:07,998 It's tiny. It's a pinpoint compared to 553 00:31:08,099 --> 00:31:09,433 our enormous galaxy. 554 00:31:09,534 --> 00:31:13,003 Our galaxy has 200 or more billion stars in it. 555 00:31:13,104 --> 00:31:16,373 And M60-UCD1 only has 140 million. 556 00:31:16,474 --> 00:31:20,377 But they're packed into this incredibly tight volume. 557 00:31:20,478 --> 00:31:22,679 ROWE: The night sky inside the galaxy 558 00:31:22,780 --> 00:31:25,549 would look very different from our own. 559 00:31:25,650 --> 00:31:28,018 PLAIT: On Earth, when you look at the night sky, 560 00:31:28,119 --> 00:31:30,354 you see a few thousand stars. 561 00:31:30,455 --> 00:31:32,756 But if you were in M60-UCD1, 562 00:31:32,857 --> 00:31:35,092 you wouldn't just see a few thousand stars. 563 00:31:35,193 --> 00:31:38,195 You would see hundreds of thousands of stars 564 00:31:38,296 --> 00:31:40,998 in the night sky. That would be amazing. 565 00:31:47,505 --> 00:31:49,273 ROWE: As the astronomers look deeper 566 00:31:49,374 --> 00:31:51,909 into the heart of this tiny galaxy, 567 00:31:52,010 --> 00:31:55,212 Things got even weirder. 568 00:31:55,313 --> 00:31:58,916 They found a supermassive black hole much bigger 569 00:31:59,017 --> 00:32:01,285 than expected. 570 00:32:01,386 --> 00:32:05,822 It actually has a black hole that's bigger, five times bigger 571 00:32:05,924 --> 00:32:07,157 than the black hole at the center of 572 00:32:07,258 --> 00:32:09,192 our Milky Way Galaxy. 573 00:32:09,260 --> 00:32:12,796 PLAIT: When we see supermassive black holes inside of galaxies, 574 00:32:12,897 --> 00:32:16,199 they tend to scale with the size of the galaxy itself. 575 00:32:16,301 --> 00:32:19,970 A bigger galaxy has a bigger supermassive black hole. 576 00:32:20,071 --> 00:32:22,205 Why does such a tiny little object 577 00:32:22,307 --> 00:32:25,742 have such an oversized central black hole? 578 00:32:25,843 --> 00:32:27,945 ROWE: The only possible explanation? 579 00:32:28,046 --> 00:32:32,683 This tiny galaxy was once much larger. 580 00:32:32,784 --> 00:32:35,752 These galaxies might have begun their lives as, in fact, 581 00:32:35,853 --> 00:32:37,821 much bigger galaxies. 582 00:32:37,922 --> 00:32:40,290 And that what we see today, it was really just the very 583 00:32:40,391 --> 00:32:43,293 central, densest part of a much larger galaxy 584 00:32:44,963 --> 00:32:48,298 ROWE: Based on the size of its supermassive black hole, 585 00:32:48,366 --> 00:32:51,301 M60-UCD1 may once 586 00:32:51,402 --> 00:32:54,304 have contained many billions of stars. 587 00:32:54,405 --> 00:32:57,708 Something captured them, 588 00:32:57,809 --> 00:33:00,777 and we don't have to look far to find the aggressor -- 589 00:33:00,878 --> 00:33:03,080 A nearby super galaxy with 590 00:33:03,181 --> 00:33:07,718 lots of gravitational firepower -- M60. 591 00:33:07,819 --> 00:33:11,321 M60 is a monster. It has a trillion stars in it. 592 00:33:11,422 --> 00:33:12,689 It's bigger than the Milky Way, 593 00:33:12,790 --> 00:33:14,558 and we're pretty big. 594 00:33:14,659 --> 00:33:17,995 ROWE: The battle was not a full-on frontal assault. 595 00:33:18,096 --> 00:33:23,367 M60 raided its smaller opponent, capturing its troops. 596 00:33:23,468 --> 00:33:26,670 SUTTER: This is more of a stealthy guerrilla hit and run 597 00:33:26,771 --> 00:33:28,271 where we're gonna move in, 598 00:33:28,373 --> 00:33:30,907 pick off some of your troops, and then get out 599 00:33:31,009 --> 00:33:33,510 before you even notice. 600 00:33:33,611 --> 00:33:36,646 MINGARELLI: All that's left from one of these drive-by 601 00:33:36,748 --> 00:33:38,015 galaxy interactions 602 00:33:38,116 --> 00:33:41,385 is this supermassive black hole with a fraction 603 00:33:41,486 --> 00:33:43,453 of its original stars. 604 00:33:43,554 --> 00:33:48,358 ROWE: The conflict devastated M60-UCD1. 605 00:33:48,459 --> 00:33:51,962 Over 98% of its stellar army were captured 606 00:33:52,063 --> 00:33:54,431 and became prisoners of war. 607 00:33:54,532 --> 00:33:57,734 SUTTER: It used to be a big galaxy, 608 00:33:57,835 --> 00:34:00,203 but it suffered one too many defeats. 609 00:34:00,304 --> 00:34:02,606 And now it's a -- It's a fallen empire. 610 00:34:02,707 --> 00:34:05,075 PLAIT: We can frame this battle 611 00:34:05,176 --> 00:34:09,079 between M60 and M60-UCD1 as just a battle. 612 00:34:09,180 --> 00:34:11,314 But in fact, it's a slaughter. 613 00:34:11,416 --> 00:34:13,417 It's a massacre. 614 00:34:13,518 --> 00:34:17,554 SUTTER: These small galaxies get all their troops removed, 615 00:34:17,655 --> 00:34:19,322 but the HQ, 616 00:34:19,424 --> 00:34:21,458 the supermassive black hole remains, 617 00:34:21,559 --> 00:34:24,294 but it doesn't have any troops left. 618 00:34:24,395 --> 00:34:28,031 ROWE: Eventually, M60 will conquer its battered opponent, 619 00:34:28,132 --> 00:34:32,569 destroying what's left of the compact galaxy. 620 00:34:32,703 --> 00:34:34,304 PLAIT: It'll get ripped apart even further, 621 00:34:34,405 --> 00:34:36,506 and more and more stars will be consumed 622 00:34:36,607 --> 00:34:37,974 by the bigger galaxy. 623 00:34:38,076 --> 00:34:41,578 So chances are this little dwarf is eventually going to 624 00:34:41,679 --> 00:34:45,515 be pulled apart and become a part of M60. 625 00:34:45,616 --> 00:34:48,718 ROWE: In the great game of galactic warfare, 626 00:34:48,820 --> 00:34:50,687 losing can be catastrophic. 627 00:34:50,788 --> 00:34:53,023 For weak and small galaxies, 628 00:34:53,091 --> 00:34:55,492 resistance is futile. 629 00:34:57,728 --> 00:35:00,530 Pillaged for resource is by their more powerful opponents, 630 00:35:00,631 --> 00:35:03,333 they slowly become burnt-out wrecks. 631 00:35:06,003 --> 00:35:11,007 But some peaceful galaxies face an equally terrible fate. 632 00:35:11,109 --> 00:35:12,909 They starve to death. 633 00:35:24,088 --> 00:35:26,223 ROWE: Cosmic wars are vicious. 634 00:35:26,324 --> 00:35:29,192 They destroy many galaxies, 635 00:35:29,293 --> 00:35:33,463 but violent conflicts can also give galaxies new life. 636 00:35:35,366 --> 00:35:36,266 Case in point, 637 00:35:36,367 --> 00:35:40,570 galaxy NGC 4485. 638 00:35:41,706 --> 00:35:44,407 HOPKINS: NGC 4485 has a nickname of the two-faced galaxy, 639 00:35:44,509 --> 00:35:45,742 like the Batman villain, 640 00:35:45,843 --> 00:35:48,612 because it has two different halves of the galaxy 641 00:35:48,713 --> 00:35:50,080 doing completely different things. 642 00:35:50,181 --> 00:35:53,150 Half of the galaxy is sort of old and calm 643 00:35:53,251 --> 00:35:54,517 and relatively quiescent, 644 00:35:54,585 --> 00:35:57,454 whereas half of it appears to be undergoing a sort of 645 00:35:57,555 --> 00:36:00,423 fireworks display of new star formation. 646 00:36:01,826 --> 00:36:04,060 ROWE: Why are new stars only born 647 00:36:04,162 --> 00:36:06,329 in one half of this galaxy? 648 00:36:08,432 --> 00:36:09,733 We found a clue on the edge of 649 00:36:09,834 --> 00:36:14,504 a photo taken by the Hubble Space Telescope. 650 00:36:14,605 --> 00:36:18,441 It was evidence of an attack by another galaxy. 651 00:36:18,543 --> 00:36:22,179 We think that another galaxy passed through it just off 652 00:36:22,280 --> 00:36:24,814 center in a way that strongly perturbed 653 00:36:24,916 --> 00:36:27,751 the gas on one half of the galaxy. 654 00:36:29,887 --> 00:36:32,522 ROWE: The two-faced galaxy skirmish gave it 655 00:36:32,623 --> 00:36:34,090 a gravitational jolt, 656 00:36:34,192 --> 00:36:37,093 forcing clouds of gas together. 657 00:36:37,195 --> 00:36:40,263 When we think of galaxies, we think of stars, 658 00:36:40,364 --> 00:36:42,032 and of course, galaxies are made of stars. 659 00:36:42,133 --> 00:36:44,367 But, of course, gas is the stuff that 660 00:36:44,468 --> 00:36:45,702 stars are made of. 661 00:36:48,172 --> 00:36:49,873 ROWE: When two galaxies collide, 662 00:36:49,974 --> 00:36:51,741 the gravitational duel can trigger 663 00:36:51,876 --> 00:36:54,077 a huge burst of star formation. 664 00:36:58,349 --> 00:37:00,650 You need something to give a galaxy a push, 665 00:37:00,751 --> 00:37:03,486 and that's exactly what a galaxy collision does. 666 00:37:03,588 --> 00:37:06,823 BASRI: And when gas clouds collide, they compress. 667 00:37:06,924 --> 00:37:10,093 And when they compress, you get knots in them that can 668 00:37:10,194 --> 00:37:12,696 compress more and form stars. 669 00:37:14,732 --> 00:37:16,533 So you can think of these collisions as very 670 00:37:16,634 --> 00:37:17,767 violent events, 671 00:37:17,868 --> 00:37:21,171 but ultimately, it can breathe new life into a galaxy. 672 00:37:21,272 --> 00:37:25,308 ROWE: But the spoils of war don't last long. 673 00:37:25,409 --> 00:37:28,445 SUTTER: In the short term, the victor galaxy can 674 00:37:28,546 --> 00:37:31,948 come out glorious with -- With so many new stars. 675 00:37:32,049 --> 00:37:35,352 But this celebration is short-lived, because that round 676 00:37:35,453 --> 00:37:40,991 of star formation quickly uses up the material available. 677 00:37:41,092 --> 00:37:44,127 If a galaxy wants to stay alive, it has to feed on 678 00:37:44,228 --> 00:37:46,162 other galaxies. 679 00:37:46,264 --> 00:37:50,066 ROWE: So galaxies constantly need to raid new targets, 680 00:37:50,167 --> 00:37:52,602 and that raises an important question. 681 00:37:52,703 --> 00:37:55,538 What happens if there's a galaxy just alone in space? 682 00:37:55,640 --> 00:37:58,675 Nothing else is colliding with it, sort of a pacifist galaxy. 683 00:38:00,244 --> 00:38:03,346 ROWE: The poster child for these peace-loving galaxies 684 00:38:03,447 --> 00:38:06,216 is NGC 1277. 685 00:38:07,518 --> 00:38:11,321 STRAUGHN: NGC 1277 is a very peculiar galaxy. 686 00:38:11,422 --> 00:38:15,925 It's pretty big, and its stars are extremely old. 687 00:38:16,027 --> 00:38:18,461 HOPKINS: It basically hasn't formed new stars in the last 688 00:38:18,562 --> 00:38:19,963 10 billion years, 689 00:38:20,064 --> 00:38:23,300 so it's kind of the veterans home of galaxies. 690 00:38:24,368 --> 00:38:26,770 ROWE: NGC 1277 lives in a rough 691 00:38:26,871 --> 00:38:29,506 part of the cosmos called the Perseus Cluster. 692 00:38:30,875 --> 00:38:35,011 Thousands of other galaxies surround NGC 1277, 693 00:38:35,112 --> 00:38:38,181 and they are all ready for a fight. 694 00:38:38,249 --> 00:38:40,016 So you might ask, why hasn't it had 695 00:38:40,117 --> 00:38:43,119 encounters with other galaxies that might rejuvenate it? 696 00:38:44,622 --> 00:38:47,691 ROWE: The answer, once again, is gravity. 697 00:38:47,792 --> 00:38:53,229 NGC 1277 sits inside this massive galaxy cluster 698 00:38:53,331 --> 00:38:54,564 that has a ton of mass, 699 00:38:54,699 --> 00:38:56,900 and if you look at its position, it's fairly near 700 00:38:57,001 --> 00:38:58,468 the center of the cluster. 701 00:39:00,805 --> 00:39:03,506 ROWE: The combined gravity of thousands of galaxies 702 00:39:03,607 --> 00:39:06,109 pulls on NGC 1277, 703 00:39:06,210 --> 00:39:10,513 accelerating it to two million miles an hour. 704 00:39:13,250 --> 00:39:14,984 STRAUGHN: And so it has spent the last 705 00:39:15,086 --> 00:39:17,654 few billion years traveling faster and faster. 706 00:39:17,755 --> 00:39:19,889 Until now, it's almost at its fastest pace. 707 00:39:22,793 --> 00:39:24,227 HOPKINS: It's very hard for gravity 708 00:39:24,328 --> 00:39:26,763 to catch it or catch one of its neighbors 709 00:39:26,864 --> 00:39:30,734 and bring them together to merge with each other. 710 00:39:30,835 --> 00:39:34,471 ROWE: NGC 1277 has no chance of 711 00:39:34,572 --> 00:39:37,574 grabbing new gas to make new stars. 712 00:39:37,675 --> 00:39:43,279 It's dying. All that has left are old red stars. 713 00:39:43,381 --> 00:39:46,649 SUTTER: When it comes to galaxies, red is dead. 714 00:39:46,751 --> 00:39:49,152 No new stars means no big stars, 715 00:39:49,253 --> 00:39:52,922 no blue stars, just small dim red dwarfs. 716 00:39:57,962 --> 00:40:01,765 ROWE: Galaxies that don't fight just fade away. 717 00:40:01,866 --> 00:40:03,466 THALLER: And at that point, the history of 718 00:40:03,567 --> 00:40:05,502 the universe becomes really kind of boring. 719 00:40:05,603 --> 00:40:08,171 All the stars will simply start to die out. 720 00:40:08,272 --> 00:40:09,739 Eventually, there will be the last 721 00:40:09,840 --> 00:40:11,341 star formed in the Milky Way, 722 00:40:11,442 --> 00:40:13,877 with no new galaxy bringing fresh material. 723 00:40:13,978 --> 00:40:17,046 Without galaxy collisions, the universe dies. 724 00:40:17,148 --> 00:40:24,120 ♪♪ 725 00:40:24,221 --> 00:40:27,090 ROWE: Galactic battles mix things up 726 00:40:27,191 --> 00:40:29,526 and replenish gas supplies, 727 00:40:29,627 --> 00:40:33,530 and our own galaxy has reaped the benefits. 728 00:40:33,631 --> 00:40:38,401 Our Milky Way Galaxy fought a massive battle, 729 00:40:38,502 --> 00:40:41,805 but that battle may have been necessary to build 730 00:40:41,906 --> 00:40:44,908 solar systems like the one we live in right now. 731 00:40:48,779 --> 00:40:51,381 ROWE: Clashes with the Sagittarius Dwarf Galaxy 732 00:40:51,482 --> 00:40:54,517 occurred at the same time the sun formed. 733 00:40:56,086 --> 00:40:58,321 BULLOCK: It's possible that we owe our very 734 00:40:58,422 --> 00:41:02,792 existence to the collision with the Sagittarius Dwarf Galaxy. 735 00:41:02,893 --> 00:41:05,695 TREMBLAY: Maybe the gas that ultimately gave rise 736 00:41:05,830 --> 00:41:07,764 to the birth of our solar system 737 00:41:07,865 --> 00:41:10,066 once came from another galaxy entirely. 738 00:41:12,369 --> 00:41:16,339 ROWE: So galactic wars are both creative and destructive. 739 00:41:17,641 --> 00:41:21,244 Galaxies are built from collisions, 740 00:41:21,345 --> 00:41:24,280 galaxies survive from collisions, 741 00:41:24,381 --> 00:41:29,052 and galaxies can also die from collisions. 742 00:41:29,153 --> 00:41:30,987 Far from being destructive events, 743 00:41:31,088 --> 00:41:32,689 colliding galaxies may be the reason 744 00:41:32,790 --> 00:41:34,123 that you and I are here. 745 00:41:37,127 --> 00:41:39,529 ROWE: Intergalactic warfare has revolutionized 746 00:41:39,630 --> 00:41:44,334 our understanding of how galaxies live and die. 747 00:41:44,435 --> 00:41:47,804 Ultimately, it's these galaxy mergers that are one of 748 00:41:47,905 --> 00:41:50,173 the great engines of all structure growth 749 00:41:50,274 --> 00:41:52,008 in the universe. 750 00:41:52,109 --> 00:41:55,245 OLUSEYI: These collisions got us to where we are today, 751 00:41:55,346 --> 00:41:58,314 and they're gonna determine the future of all the universe.