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These are the user uploaded subtitles that are being translated: 1 00:00:04,438 --> 00:00:09,386 Imagine a universe with no stars... 2 00:00:09,410 --> 00:00:12,011 a dark, endless night. 3 00:00:14,081 --> 00:00:17,961 This is not some Sci-Fi nightmare. 4 00:00:17,985 --> 00:00:20,931 This is our future. 5 00:00:20,955 --> 00:00:24,668 There will definitely be a point in the future when, you look up, 6 00:00:24,692 --> 00:00:27,137 you will no longer be able to see stars. 7 00:00:27,161 --> 00:00:29,606 Things really will get darker and darker, 8 00:00:29,630 --> 00:00:33,844 until there will be almost no memory of light left. 9 00:00:33,868 --> 00:00:39,016 For billions of years, stars brought life to the universe. 10 00:00:39,040 --> 00:00:45,355 The fact that you exist at all is because of stars. 11 00:00:45,379 --> 00:00:50,694 Now, they're dying out in a star apocalypse. 12 00:00:50,718 --> 00:00:53,096 The effect could be tremendous. 13 00:00:53,120 --> 00:00:56,299 It can permeate throughout the universe. 14 00:00:56,323 --> 00:00:58,802 What's causing the die-off, 15 00:00:58,826 --> 00:01:03,874 and what happens to life when the lights go out? 16 00:01:03,898 --> 00:01:06,143 Eventually, the whole entire universe 17 00:01:06,167 --> 00:01:09,368 starts to get a little bit weird. 18 00:01:15,543 --> 00:01:18,522 Captions by vitac... www.vitac.com 19 00:01:18,546 --> 00:01:21,580 captions paid for by discovery communications 20 00:01:23,751 --> 00:01:25,896 for over 4.5 billion years, 21 00:01:25,920 --> 00:01:29,755 the sun has bathed our home planet with light. 22 00:01:31,592 --> 00:01:36,373 Its bright, stable glow helps life flourish, 23 00:01:36,397 --> 00:01:38,475 but hidden in the night sky, 24 00:01:38,499 --> 00:01:43,213 other planetary systems haven't been so lucky. 25 00:01:43,237 --> 00:01:45,315 Hanging right above your head every night, 26 00:01:45,339 --> 00:01:49,853 we see up there these dead corpses of stars. 27 00:01:49,877 --> 00:01:57,060 400 light-years from earth lies a system called SDSSJ1228. 28 00:01:57,084 --> 00:01:59,196 A disk of debris orbits 29 00:01:59,220 --> 00:02:03,967 the faintly glowing leftovers of a dead star. 30 00:02:03,991 --> 00:02:06,303 J1228 is a dead star. 31 00:02:06,327 --> 00:02:08,972 It is a core of a star that had aged, 32 00:02:08,996 --> 00:02:11,908 blown off its outer layers, revealed the core... 33 00:02:11,932 --> 00:02:13,643 which is about the size of the earth, 34 00:02:13,667 --> 00:02:15,812 but has about half the mass of the star in it. 35 00:02:15,836 --> 00:02:17,636 And we call these "white dwarfs." 36 00:02:25,012 --> 00:02:27,858 May, 2018. 37 00:02:27,882 --> 00:02:30,894 Astronomers investigated J1228 38 00:02:30,918 --> 00:02:34,397 using the world's largest optical telescope... 39 00:02:34,421 --> 00:02:38,468 the Gran Telescopio Canarias. 40 00:02:38,492 --> 00:02:42,038 They discovered what appears to be a ball of iron 41 00:02:42,062 --> 00:02:44,641 orbiting the white dwarf. 42 00:02:44,665 --> 00:02:48,545 The lump of metal, less than 400 miles across, 43 00:02:48,569 --> 00:02:52,916 could be the exposed core of a destroyed planet. 44 00:02:52,940 --> 00:02:56,853 It's a clue to this system's past. 45 00:02:56,877 --> 00:02:58,221 It's always a little poignant 46 00:02:58,245 --> 00:03:01,424 when you see evidence of a planet around a dead star. 47 00:03:01,448 --> 00:03:03,493 You know, you think back of when that star was shining, 48 00:03:03,517 --> 00:03:05,996 and could there have been life in that solar system? 49 00:03:06,020 --> 00:03:11,067 The J1228 system is a cosmic graveyard. 50 00:03:11,091 --> 00:03:14,471 It might look different than our solar system, 51 00:03:14,495 --> 00:03:18,041 but this is our future. 52 00:03:18,065 --> 00:03:22,512 This discovery of a dead planet orbiting a dead star 53 00:03:22,536 --> 00:03:24,848 is like looking into a crystal ball. 54 00:03:24,872 --> 00:03:28,018 And is it the future of our own solar system? 55 00:03:28,042 --> 00:03:29,352 Yep. 56 00:03:29,376 --> 00:03:31,188 For a glimpse into your future, you know, 57 00:03:31,212 --> 00:03:33,278 all you need to do is look up. 58 00:03:37,484 --> 00:03:42,732 Just like J1228, our sun will die, 59 00:03:42,756 --> 00:03:46,002 killing off earth in the process. 60 00:03:46,026 --> 00:03:50,240 This terrifying fate will play out across the galaxy 61 00:03:50,264 --> 00:03:53,343 in a star apocalypse. 62 00:03:53,367 --> 00:03:56,780 Our sun is a fairly common type of star in the milky way, 63 00:03:56,804 --> 00:03:59,316 and so, other stars in the milky way 64 00:03:59,340 --> 00:04:01,551 will undergo the same sort of fate as the sun. 65 00:04:01,575 --> 00:04:03,086 They will end up as white dwarfs. 66 00:04:03,110 --> 00:04:06,223 And so, any other planets out there orbiting sun-like stars 67 00:04:06,247 --> 00:04:08,046 will undergo a similar fate. 68 00:04:10,951 --> 00:04:12,996 Once the stars like our sun have died out, 69 00:04:13,020 --> 00:04:14,164 what's gonna happen? 70 00:04:14,188 --> 00:04:18,602 Could life still survive around white dwarfs? 71 00:04:18,626 --> 00:04:21,504 To understand the fate of sun-like stars, 72 00:04:21,528 --> 00:04:23,340 we have to look inside them. 73 00:04:23,364 --> 00:04:28,578 Buried within are clues to how they live, and why they die. 74 00:04:28,602 --> 00:04:31,414 The core, the very center, that's where the action is. 75 00:04:31,438 --> 00:04:34,484 That's where the star is fusing light elements 76 00:04:34,508 --> 00:04:36,686 into heavier elements. 77 00:04:36,710 --> 00:04:38,321 And that works like a hydrogen bomb. 78 00:04:38,345 --> 00:04:39,956 It's the same thing. 79 00:04:39,980 --> 00:04:43,193 If you compress hydrogen enough, it gets very hot, 80 00:04:43,217 --> 00:04:44,828 and the pressure gets very high, 81 00:04:44,852 --> 00:04:49,032 and if fuses into helium, and generates energy... heat. 82 00:04:49,056 --> 00:04:52,435 And that's what's happening in the core of every star. 83 00:04:52,459 --> 00:04:54,271 Because of their enormous mass, 84 00:04:54,295 --> 00:04:57,507 stars have huge amounts of gravity. 85 00:04:57,531 --> 00:05:02,746 This gravity pushes inwards, trying to collapse the star, 86 00:05:02,770 --> 00:05:07,951 but fusion energy from the core stops that from happening. 87 00:05:07,975 --> 00:05:11,054 It's really this sort of very balanced dance 88 00:05:11,078 --> 00:05:14,858 between gravity pushing in, fusion energy pushing out. 89 00:05:14,882 --> 00:05:18,962 You can think of a star as losing energy, 90 00:05:18,986 --> 00:05:20,764 continuously, to the outside world/ 91 00:05:20,788 --> 00:05:23,366 and gravity is saying, "yes, I'm gonna take over." 92 00:05:23,390 --> 00:05:27,637 But, no, the nuclear reactions inside a star 93 00:05:27,661 --> 00:05:30,407 replenish the energy that's lost, 94 00:05:30,431 --> 00:05:33,943 and keep the star hot and pressurized inside, 95 00:05:33,967 --> 00:05:40,216 so that the pressure-gravity balance can be maintained. 96 00:05:40,240 --> 00:05:43,653 This balance keeps sun-like stars alive 97 00:05:43,677 --> 00:05:46,823 for up to 10 billion years, 98 00:05:46,847 --> 00:05:51,661 until the star's gas tank runs dry. 99 00:05:51,685 --> 00:05:53,396 It's gonna run out of fuel. 100 00:05:53,420 --> 00:05:56,132 And when that happens, it's going to die. 101 00:05:56,156 --> 00:05:57,367 But what is that gonna look like? 102 00:05:57,391 --> 00:05:59,024 How is this gonna happen? 103 00:06:00,894 --> 00:06:02,739 One hundred million years ago, 104 00:06:02,763 --> 00:06:08,778 things in the J1228 system started to get ugly. 105 00:06:08,802 --> 00:06:14,384 First, the star grew large... really large. 106 00:06:14,408 --> 00:06:17,487 Once the center starts fusing heavier elements, 107 00:06:17,511 --> 00:06:19,022 the outside will swell 108 00:06:19,046 --> 00:06:22,826 into what will eventually be a red giant star. 109 00:06:22,850 --> 00:06:28,131 J1228 transformed into a red giant. 110 00:06:28,155 --> 00:06:29,799 Its outer layers blew off, 111 00:06:29,823 --> 00:06:34,504 extending out over 40 million miles. 112 00:06:34,528 --> 00:06:37,941 When stars like our sun die, it's not a quiet affair. 113 00:06:37,965 --> 00:06:41,077 It's very violent, and ugly, and messy. 114 00:06:41,101 --> 00:06:42,746 They turn into red giants, 115 00:06:42,770 --> 00:06:44,981 and they turn themselves inside out, 116 00:06:45,005 --> 00:06:49,152 and vomit all over the solar system. 117 00:06:49,176 --> 00:06:52,756 When J1228 swelled into a red giant, 118 00:06:52,780 --> 00:06:58,261 nearby planets were stuck in a kill zone. 119 00:06:58,285 --> 00:07:01,765 The dying star engulfed them, or fried them 120 00:07:01,789 --> 00:07:05,635 with temperatures of over 1,200 degrees Fahrenheit. 121 00:07:05,659 --> 00:07:08,338 Atmospheres disappeared. 122 00:07:08,362 --> 00:07:10,940 Oceans boiled away, 123 00:07:10,964 --> 00:07:15,678 but one planet survived J1228's death throes. 124 00:07:15,702 --> 00:07:20,350 Here's a case where a planet survived, in some sense, 125 00:07:20,374 --> 00:07:23,653 the death of its own star, and it's still hanging around, 126 00:07:23,677 --> 00:07:27,991 still hanging on, hoping for something new. 127 00:07:28,015 --> 00:07:30,427 The red giant's expanding outer layers 128 00:07:30,451 --> 00:07:32,951 separated from the star's core. 129 00:07:34,955 --> 00:07:41,738 With no active fusion, the core collapsed into a white dwarf. 130 00:07:41,762 --> 00:07:43,807 The white dwarf's dense gravity 131 00:07:43,831 --> 00:07:48,411 then went to work on the one surviving planet. 132 00:07:48,435 --> 00:07:51,981 The planet that might've been orbiting the normal star 133 00:07:52,005 --> 00:07:55,752 can gradually spiral in toward the white dwarf, 134 00:07:55,776 --> 00:07:58,755 and then, eventually, the gravity of the white dwarf pulls 135 00:07:58,779 --> 00:08:02,158 on the near side of the planet more than on the far side, 136 00:08:02,182 --> 00:08:04,461 and that tears it apart. 137 00:08:04,485 --> 00:08:07,063 What we're seeing here is a dead star 138 00:08:07,087 --> 00:08:10,188 dining on its own solar system. 139 00:08:11,925 --> 00:08:14,993 That's what is in the future for the sun. 140 00:08:17,998 --> 00:08:23,146 J1228 feasted on the remains of its rocky worlds, 141 00:08:23,170 --> 00:08:29,486 leaving behind a disk of debris and the planetary core. 142 00:08:29,510 --> 00:08:33,590 It's a glimpse of earth's future. 143 00:08:33,614 --> 00:08:35,892 What happened here around this white dwarf 144 00:08:35,916 --> 00:08:37,227 is gonna happen to earth. 145 00:08:37,251 --> 00:08:39,596 It's gonna be stripped of its atmosphere, 146 00:08:39,620 --> 00:08:41,731 its crust, and its mantle, 147 00:08:41,755 --> 00:08:46,469 and the only thing that will remain will be the core. 148 00:08:46,493 --> 00:08:49,639 Fried and ripped apart by a dying star... 149 00:08:49,663 --> 00:08:52,175 not a good way to go. 150 00:08:52,199 --> 00:08:54,310 Fortunately, for life on earth, 151 00:08:54,334 --> 00:08:58,014 our own sun isn't dying just yet. 152 00:08:58,038 --> 00:08:59,849 The sun is middle-aged. 153 00:08:59,873 --> 00:09:01,518 It's 4.5 billion years old, 154 00:09:01,542 --> 00:09:04,821 and it's going to go on for another 5 or 6 billion years. 155 00:09:04,845 --> 00:09:06,356 We've got a little bit of time 156 00:09:06,380 --> 00:09:11,094 before our sun pukes all over the solar system. 157 00:09:11,118 --> 00:09:13,596 Our home planet may be safe for now, 158 00:09:13,620 --> 00:09:16,733 but systems like J1228 show us 159 00:09:16,757 --> 00:09:20,870 that sun-like stars are destined to die, 160 00:09:20,894 --> 00:09:24,707 killing off any life orbiting them. 161 00:09:24,731 --> 00:09:27,911 But sun-like stars aren't the only stars 162 00:09:27,935 --> 00:09:30,446 dying across the cosmos. 163 00:09:30,470 --> 00:09:35,285 There are others out there, and they're all doomed. 164 00:09:35,309 --> 00:09:38,354 There's a wonderful rainbow of stars 165 00:09:38,378 --> 00:09:40,156 out there, of all different shapes, 166 00:09:40,180 --> 00:09:43,159 all different sizes, and all different colors. 167 00:09:43,183 --> 00:09:44,894 We're talking down to, you know, 168 00:09:44,918 --> 00:09:46,796 fractions of the mass of the sun, 169 00:09:46,820 --> 00:09:50,033 up to hundreds of times the mass of the sun. 170 00:09:50,057 --> 00:09:53,937 When it comes to the star apocalypse, size matters. 171 00:09:53,961 --> 00:09:57,862 The bigger and brighter the star, the faster it dies. 172 00:10:17,517 --> 00:10:21,786 Our universe is a vast expanse of death and destruction. 173 00:10:23,924 --> 00:10:29,327 All of the stars are destined to die, but not all at once. 174 00:10:30,964 --> 00:10:33,176 There's not going to be one particular point 175 00:10:33,200 --> 00:10:35,845 where all the lights turn off at the same time. 176 00:10:35,869 --> 00:10:38,481 It's more like a power outage, 177 00:10:38,505 --> 00:10:42,085 where different grids go off at different times, until, 178 00:10:42,109 --> 00:10:46,456 like, there's the one last light bulb that'll just go off. 179 00:10:46,480 --> 00:10:51,461 This is because stars come in different sizes. 180 00:10:51,485 --> 00:10:53,930 The way a star dies has everything to do with 181 00:10:53,954 --> 00:10:55,898 the amount of mass it started life with. 182 00:10:55,922 --> 00:10:59,769 It carries that all the way through its lifetime. 183 00:10:59,793 --> 00:11:02,672 The sun is a medium-sized star 184 00:11:02,696 --> 00:11:06,909 living a stable existence for billions of years. 185 00:11:06,933 --> 00:11:09,746 Giant stars are different. 186 00:11:09,770 --> 00:11:13,549 They live fast, and die young. 187 00:11:13,573 --> 00:11:17,220 A star like the sun, which is a medium-sized star, 188 00:11:17,244 --> 00:11:19,656 it lives about 10 billion years. 189 00:11:19,680 --> 00:11:21,457 The really massive stars, 190 00:11:21,481 --> 00:11:25,328 they live maybe 10 million years. 191 00:11:25,352 --> 00:11:28,731 Massive stars can be tens or even hundreds of times 192 00:11:28,755 --> 00:11:31,734 more massive than the sun. 193 00:11:31,758 --> 00:11:35,905 When it comes to life span, that's a problem. 194 00:11:35,929 --> 00:11:40,743 A massive star has more fuel to burn, in a nuclear sense. 195 00:11:40,767 --> 00:11:43,446 So, you might naively think that it lasts longer, 196 00:11:43,470 --> 00:11:45,948 but it's the exact opposite. 197 00:11:45,972 --> 00:11:51,521 Massive stars can only access hydrogen fuel in their core. 198 00:11:51,545 --> 00:11:54,490 The rest is trapped in the outer layers, 199 00:11:54,514 --> 00:11:57,393 and can't be used as fuel. 200 00:11:57,417 --> 00:11:59,729 If there's hydrogen in the core, you're good. 201 00:11:59,753 --> 00:12:03,199 If there's hydrogen outside of the core, it can't be used. 202 00:12:03,223 --> 00:12:06,357 If it's not in your fuel tank, it's not doing you any good. 203 00:12:07,994 --> 00:12:13,643 Massive stars also have more gravity than smaller stars, 204 00:12:13,667 --> 00:12:17,413 so they have to burn their hydrogen fuel faster 205 00:12:17,437 --> 00:12:19,704 to prevent the star from collapsing. 206 00:12:21,708 --> 00:12:23,786 They burn their candle on both ends. 207 00:12:23,810 --> 00:12:25,688 Because of their incredible mass, 208 00:12:25,712 --> 00:12:27,790 their fusion reactions in the core 209 00:12:27,814 --> 00:12:30,326 happen at an incredible rate. 210 00:12:30,350 --> 00:12:32,929 Giant stars are kind of fast and furious. 211 00:12:32,953 --> 00:12:34,697 They are bright. 212 00:12:34,721 --> 00:12:37,856 They live their life, and they die very quickly. 213 00:12:40,026 --> 00:12:42,605 When a giant star's fuel runs out, 214 00:12:42,629 --> 00:12:44,907 the core collapses catastrophically 215 00:12:44,931 --> 00:12:48,377 under the overwhelming force of gravity. 216 00:12:48,401 --> 00:12:51,536 And then, boom, supernova. 217 00:12:58,512 --> 00:13:00,189 The death of a giant star 218 00:13:00,213 --> 00:13:03,081 triggers one of the biggest bangs in the universe. 219 00:13:07,220 --> 00:13:11,156 The blast would instantly vaporize nearby planets. 220 00:13:14,995 --> 00:13:19,876 But these star deaths are also critical for life. 221 00:13:19,900 --> 00:13:22,912 When massive stars die, they release heavy elements 222 00:13:22,936 --> 00:13:25,882 they've been making through the course of their lives. 223 00:13:25,906 --> 00:13:27,884 And sometimes, they even make new ones. 224 00:13:27,908 --> 00:13:32,922 And it's these heavier elements that are essential for life. 225 00:13:32,946 --> 00:13:35,458 We owe our existence to stars 226 00:13:35,482 --> 00:13:38,316 that formed billions of years ago. 227 00:13:42,789 --> 00:13:47,870 In may of 2018, we spotted evidence of ancient stars 228 00:13:47,894 --> 00:13:50,373 creating the stuff of life. 229 00:13:50,397 --> 00:13:53,009 We picked up an infrared light signal 230 00:13:53,033 --> 00:13:59,304 from a distant galaxy named MACS1149-JD1. 231 00:14:01,141 --> 00:14:04,142 The signal was ionized oxygen. 232 00:14:06,613 --> 00:14:10,459 It's been traveling for 13.3 billion years, 233 00:14:10,483 --> 00:14:15,097 so the oxygen formed when the universe was very young... 234 00:14:15,121 --> 00:14:20,770 just 500 million years after the big bang. 235 00:14:20,794 --> 00:14:26,709 This oxygen formed in the hearts of massive stars. 236 00:14:26,733 --> 00:14:28,277 The presence of oxygen tells us 237 00:14:28,301 --> 00:14:31,581 that there needed to be massive stars in the early universe 238 00:14:31,605 --> 00:14:34,016 in order to synthesize hydrogen and helium 239 00:14:34,040 --> 00:14:36,352 into heavier elements, like oxygen, 240 00:14:36,376 --> 00:14:38,988 and then explode to eject that oxygen 241 00:14:39,012 --> 00:14:42,814 back into the interstellar and intergalactic medium. 242 00:14:44,918 --> 00:14:49,220 Extreme pressure in the cores of the stars produces oxygen... 243 00:14:51,524 --> 00:14:55,905 ...and other elements, like carbon and nitrogen. 244 00:14:55,929 --> 00:15:00,142 Supernova blasts spread these elements across the universe, 245 00:15:00,166 --> 00:15:04,513 helping to create new generations of stars, 246 00:15:04,537 --> 00:15:08,784 and, most importantly, us. 247 00:15:08,808 --> 00:15:11,787 If there is one single fact that you should care about 248 00:15:11,811 --> 00:15:15,391 in all of science... and this is my favorite fact... 249 00:15:15,415 --> 00:15:18,683 is that you and I are a consequence of star death. 250 00:15:22,455 --> 00:15:24,400 Before you can have life, you need to have 251 00:15:24,424 --> 00:15:27,303 the kind of elements out of which life forms. 252 00:15:27,327 --> 00:15:29,272 You need carbon. You need nitrogen. 253 00:15:29,296 --> 00:15:30,640 You need oxygen. 254 00:15:30,664 --> 00:15:32,508 You need the elements that are the backbone 255 00:15:32,532 --> 00:15:36,112 to the biology that makes us possible. 256 00:15:36,136 --> 00:15:37,580 Where did those elements come from? 257 00:15:37,604 --> 00:15:38,881 Well, they came from stars. 258 00:15:38,905 --> 00:15:41,350 They came from stars that formed in the early universe, 259 00:15:41,374 --> 00:15:44,153 before even the sun existed. 260 00:15:44,177 --> 00:15:46,555 The huge size of massive stars 261 00:15:46,579 --> 00:15:49,525 quickly signs their death warrants. 262 00:15:49,549 --> 00:15:55,998 Their explosive ends help create new stars, and even life. 263 00:15:56,022 --> 00:16:01,225 The fact that you exist at all is because of stars. 264 00:16:02,562 --> 00:16:05,808 But, probing galaxies across the universe, 265 00:16:05,832 --> 00:16:08,477 we've discovered something else. 266 00:16:08,501 --> 00:16:12,381 The star apocalypse isn't just killing stars. 267 00:16:12,405 --> 00:16:15,751 It's stopping them from ever being born. 268 00:16:15,775 --> 00:16:17,486 Star formation is dying. 269 00:16:17,510 --> 00:16:19,956 And in fact, it's dying rather quickly. 270 00:16:19,980 --> 00:16:22,058 The universe, right before our eyes, 271 00:16:22,082 --> 00:16:24,093 is becoming a darker place. 272 00:16:24,117 --> 00:16:25,828 It's running out of fuel. 273 00:16:25,852 --> 00:16:29,153 And eventually, no more stars will be made at all. 274 00:16:51,044 --> 00:16:55,491 Life on earth follows a series of regular patterns. 275 00:16:55,515 --> 00:16:59,128 Day after day, the sun rises... 276 00:16:59,152 --> 00:17:02,198 And sets, 277 00:17:02,222 --> 00:17:06,902 and stars light up the darkness of the night sky. 278 00:17:06,926 --> 00:17:09,872 The reason I got into astronomy to begin with 279 00:17:09,896 --> 00:17:12,341 was because I grew up in a rural part of the country, 280 00:17:12,365 --> 00:17:13,809 and the sky was beautiful and dark. 281 00:17:13,833 --> 00:17:15,611 You go outside at night, and you look up, 282 00:17:15,635 --> 00:17:18,381 and you could see thousands of stars. 283 00:17:18,405 --> 00:17:20,805 But it won't be that way forever. 284 00:17:23,309 --> 00:17:27,757 2016, a network of telescopes across the world 285 00:17:27,781 --> 00:17:32,495 measured the energy outputs of over 200,000 galaxies. 286 00:17:34,521 --> 00:17:37,566 They discovered that in the past 2 billion years, 287 00:17:37,590 --> 00:17:40,958 the universe has lost half its brightness. 288 00:17:42,429 --> 00:17:44,907 The night sky is getting darker 289 00:17:44,931 --> 00:17:49,211 as stars flicker out of existence. 290 00:17:49,235 --> 00:17:50,746 About 10 billion years ago, 291 00:17:50,770 --> 00:17:52,815 the universe kind of hit its peak, 292 00:17:52,839 --> 00:17:55,251 and lots of stars were shining. 293 00:17:55,275 --> 00:17:58,187 It was an incredibly bright place, 294 00:17:58,211 --> 00:18:00,756 but in the last couple billion years, 295 00:18:00,780 --> 00:18:04,593 it's really, overall, become a less bright place. 296 00:18:04,617 --> 00:18:07,463 The darkening universe isn't just a sign 297 00:18:07,487 --> 00:18:09,899 that stars are dying. 298 00:18:09,923 --> 00:18:15,438 It seems there's a problem with star birth as well. 299 00:18:15,462 --> 00:18:17,573 When we look into the universe's past, 300 00:18:17,597 --> 00:18:19,175 what we find is that long ago, 301 00:18:19,199 --> 00:18:21,777 stars were forming at a much higher rate. 302 00:18:21,801 --> 00:18:24,146 Right now what we see is that really, 303 00:18:24,170 --> 00:18:27,950 stars are dying off faster than they're being born. 304 00:18:27,974 --> 00:18:30,352 A milky way-type galaxy, today, 305 00:18:30,376 --> 00:18:32,788 produces about seven stars per year. 306 00:18:32,812 --> 00:18:35,291 However, 11 billion years ago, 307 00:18:35,315 --> 00:18:38,850 a galaxy like our own would've produced 10 times more stars. 308 00:18:40,453 --> 00:18:43,299 In the early universe, old stars died, 309 00:18:43,323 --> 00:18:46,268 and new ones formed in their place 310 00:18:46,292 --> 00:18:48,504 from the material left over. 311 00:18:48,528 --> 00:18:51,696 It was a cycle that kept the cosmos bright. 312 00:18:52,665 --> 00:18:54,777 Not anymore. 313 00:18:54,801 --> 00:18:58,781 It kind of sucks for us. We like a bright universe. 314 00:18:58,805 --> 00:19:01,383 We like all this energy and life 315 00:19:01,407 --> 00:19:03,719 that's vibrating through the universe, 316 00:19:03,743 --> 00:19:06,589 but that's just not always going to be the case. 317 00:19:06,613 --> 00:19:09,892 The universe is already winding down. 318 00:19:12,485 --> 00:19:15,631 One of the biggest mysteries in galaxy evolution 319 00:19:15,655 --> 00:19:18,968 is figuring out how galaxies stop forming their stars. 320 00:19:18,992 --> 00:19:21,070 And we really don't know the answer yet, 321 00:19:21,094 --> 00:19:23,572 and it's really important for us to figure out why 322 00:19:23,596 --> 00:19:27,343 because in the end, stars really equal life. 323 00:19:29,969 --> 00:19:33,115 To find out what is shutting off the stars, 324 00:19:33,139 --> 00:19:35,751 we study galaxy clusters. 325 00:19:38,978 --> 00:19:41,090 These giant regions of space 326 00:19:41,114 --> 00:19:45,816 contain hundreds of galaxies bound together by gravity. 327 00:19:46,953 --> 00:19:51,233 Slowly, the clusters pull new galaxies into them, 328 00:19:51,257 --> 00:19:55,504 causing something strange to happen. 329 00:19:55,528 --> 00:19:59,408 What we see happening when a galaxy falls into a cluster 330 00:19:59,432 --> 00:20:01,343 is that its star formation is quenched. 331 00:20:01,367 --> 00:20:03,712 It's shut off. 332 00:20:03,736 --> 00:20:06,215 The cause of this quenching effect 333 00:20:06,239 --> 00:20:09,985 has baffled scientists for decades. 334 00:20:10,009 --> 00:20:13,222 Then in October of 2018, 335 00:20:13,246 --> 00:20:15,858 an international team of astronomers 336 00:20:15,882 --> 00:20:18,761 investigated this long-standing mystery. 337 00:20:20,653 --> 00:20:23,365 They tracked variations in quenching 338 00:20:23,389 --> 00:20:25,134 across 14 galaxy clusters 339 00:20:25,158 --> 00:20:29,104 and found a possible explanation. 340 00:20:29,128 --> 00:20:32,041 The ability a galaxy has to make new stars 341 00:20:32,065 --> 00:20:35,377 is related to the larger environment it finds itself in. 342 00:20:35,401 --> 00:20:38,147 In clusters of galaxies where many galaxies 343 00:20:38,171 --> 00:20:39,748 are orbiting around each other, 344 00:20:39,772 --> 00:20:44,687 we see interactions that strip gas and dust away from galaxies. 345 00:20:44,711 --> 00:20:46,555 The stuff that makes up stars 346 00:20:46,579 --> 00:20:49,046 literally just thrown off into space. 347 00:20:50,917 --> 00:20:54,363 Stars formed from dense parcels of cold gas, 348 00:20:54,387 --> 00:20:56,254 something galaxies are filled with. 349 00:20:58,091 --> 00:21:01,070 But when a galaxy is dragged into a cluster, 350 00:21:01,094 --> 00:21:03,405 everything changes. 351 00:21:03,429 --> 00:21:06,675 Clusters of galaxies contain a lot of hot gas, 352 00:21:06,699 --> 00:21:09,245 whereas you need cold gas inside of a galaxy 353 00:21:09,269 --> 00:21:10,879 in order to form stars, 354 00:21:10,903 --> 00:21:14,149 and when a galaxy is moving through this hot gas, 355 00:21:14,173 --> 00:21:17,742 then the cold gas inside is stripped away. 356 00:21:19,178 --> 00:21:20,889 If this new study is right, 357 00:21:20,913 --> 00:21:25,160 and galaxy clusters are stripping away star-forming gas, 358 00:21:25,184 --> 00:21:28,486 new starlight will become rare. 359 00:21:29,656 --> 00:21:32,034 Looking over the history of the universe 360 00:21:32,058 --> 00:21:35,337 and how much gas was out there and how much is still left, 361 00:21:35,361 --> 00:21:38,173 I think it's fair to say that most of the stars 362 00:21:38,197 --> 00:21:41,277 that will ever be made already have been made. 363 00:21:41,301 --> 00:21:43,100 They've already been born. 364 00:21:44,504 --> 00:21:47,316 Thanks to the shortage of star-forming gas, 365 00:21:47,340 --> 00:21:50,953 stars won't just be dying in the universe. 366 00:21:50,977 --> 00:21:52,955 They'll go extinct, 367 00:21:52,979 --> 00:21:56,792 and the first to go will be the largest. 368 00:21:56,816 --> 00:21:58,994 As the universe runs out of gas 369 00:21:59,018 --> 00:22:01,196 and fewer of these stars are being made, 370 00:22:01,220 --> 00:22:03,365 eventually sometime in the future, 371 00:22:03,389 --> 00:22:06,635 all the high-mass and even medium-mass stars like the sun, 372 00:22:06,659 --> 00:22:08,137 they'll be gone. 373 00:22:08,161 --> 00:22:10,606 What does that mean for life? 374 00:22:13,800 --> 00:22:16,045 Some of the brightest stars 375 00:22:16,069 --> 00:22:17,446 will disappear forever, 376 00:22:17,470 --> 00:22:20,549 begging the question, can life survive 377 00:22:20,573 --> 00:22:23,874 the monsters that dead stars leave behind? 378 00:22:24,911 --> 00:22:29,958 The long-term fate of the universe is not a pretty sight. 379 00:22:29,982 --> 00:22:34,263 Some very interesting creatures can start to appear. 380 00:22:50,870 --> 00:22:52,614 In the star apocalypse, 381 00:22:52,638 --> 00:22:56,018 the first stars to fade away will be the brightest... 382 00:22:56,042 --> 00:23:01,679 the giant stars, followed by the mid-sized suns. 383 00:23:02,849 --> 00:23:07,196 The universe will become unrecognizable. 384 00:23:07,220 --> 00:23:09,832 The far future will be a very dim universe, 385 00:23:09,856 --> 00:23:11,934 especially for creatures like us. 386 00:23:11,958 --> 00:23:16,093 If there's no more gas, no more new stars, it gets dark. 387 00:23:17,630 --> 00:23:19,108 Scared of the dark? 388 00:23:19,132 --> 00:23:21,643 You will be... 389 00:23:21,667 --> 00:23:24,113 Because 100 billion years from now, 390 00:23:24,137 --> 00:23:27,216 in the shadows of this new universe, 391 00:23:27,240 --> 00:23:30,486 monsters will come out to play. 392 00:23:30,510 --> 00:23:34,223 Now we find ourselves in the era of stars and starlight. 393 00:23:34,247 --> 00:23:36,291 What comes after you can think of 394 00:23:36,315 --> 00:23:38,916 as the era of the dead corpses of old stars. 395 00:23:40,420 --> 00:23:43,132 We already see the corpses of dead stars 396 00:23:43,156 --> 00:23:46,235 scattered throughout the cosmos... 397 00:23:46,259 --> 00:23:52,107 black holes, pulsars, white dwarfs. 398 00:23:52,131 --> 00:23:57,713 What happens when more stars die out and the dead take over? 399 00:23:57,737 --> 00:23:59,982 Can life survive? 400 00:24:00,006 --> 00:24:03,385 It's actually possible that life in the universe will survive, 401 00:24:03,409 --> 00:24:05,576 but we're going to have to get more creative. 402 00:24:06,913 --> 00:24:09,958 January 2019. 403 00:24:09,982 --> 00:24:14,830 The Gaia satellite studied 15,000 white dwarfs 404 00:24:14,854 --> 00:24:18,066 within 300 light-years of earth. 405 00:24:18,090 --> 00:24:22,571 These are the corpses of sunlight stars. 406 00:24:22,595 --> 00:24:25,140 White dwarfs are the remnants, the cores, 407 00:24:25,164 --> 00:24:27,242 of stars like the sun after they die. 408 00:24:27,266 --> 00:24:30,212 There's no more fusion going on inside of a white dwarf. 409 00:24:30,236 --> 00:24:32,781 So it's just kind of sitting there cooling off, 410 00:24:32,805 --> 00:24:36,240 but it turns out there's a slight reprieve. 411 00:24:37,543 --> 00:24:41,490 The white dwarf corpses usually cool off and dim 412 00:24:41,514 --> 00:24:44,092 over tens of billions of years. 413 00:24:44,116 --> 00:24:47,596 Gaia's data showed something different, 414 00:24:47,620 --> 00:24:50,599 something we've never seen before. 415 00:24:50,623 --> 00:24:54,558 Some of the older dead stars aren't dimming at all. 416 00:24:56,395 --> 00:24:57,873 We used to think that white dwarfs 417 00:24:57,897 --> 00:24:59,741 could really only dim over time. 418 00:24:59,765 --> 00:25:02,211 After all, there's no source of fusion, 419 00:25:02,235 --> 00:25:04,646 no source of energy in their interiors, 420 00:25:04,670 --> 00:25:07,950 but new studies with the Gaia satellite have shown 421 00:25:07,974 --> 00:25:10,886 that there must be some other energy source 422 00:25:10,910 --> 00:25:14,056 keeping those older white dwarfs shining bright. 423 00:25:16,082 --> 00:25:19,828 Something is giving these white dwarf corpses a spark, 424 00:25:19,852 --> 00:25:24,399 bringing them back from the dead as zombies. 425 00:25:24,423 --> 00:25:25,767 The leading contender 426 00:25:25,791 --> 00:25:28,570 is that the insides of white dwarfs 427 00:25:28,594 --> 00:25:30,794 actually crystallize. 428 00:25:32,331 --> 00:25:35,177 Up to 6 billion years after dying, 429 00:25:35,201 --> 00:25:38,881 the hot carbon and oxygen matter inside the white dwarf 430 00:25:38,905 --> 00:25:42,751 cools and crystallizes, becoming solid, 431 00:25:42,775 --> 00:25:46,421 giving the dead star a lifeline. 432 00:25:46,445 --> 00:25:49,525 This actually releases energy. 433 00:25:49,549 --> 00:25:51,693 As the star cools, it winds up releasing 434 00:25:51,717 --> 00:25:54,229 a little bit more energy than it otherwise would. 435 00:25:54,253 --> 00:25:59,801 This unusual heat source could warm up a nearby frozen planet, 436 00:25:59,825 --> 00:26:03,272 giving life a second chance. 437 00:26:03,296 --> 00:26:07,042 There will be some extra energy available from these objects. 438 00:26:07,066 --> 00:26:08,744 So this is the time that we have 439 00:26:08,768 --> 00:26:10,834 to cuddle up close to the zombies. 440 00:26:12,338 --> 00:26:16,785 Crystallization can rejuvenate old white dwarfs, 441 00:26:16,809 --> 00:26:19,021 and the process could even provide 442 00:26:19,045 --> 00:26:22,691 a spectacular setting for an orbiting planet. 443 00:26:22,715 --> 00:26:24,693 We have a special name 444 00:26:24,717 --> 00:26:27,496 for cooled-down crystallized carbon and oxygen. 445 00:26:27,520 --> 00:26:29,398 We call them diamonds. 446 00:26:29,422 --> 00:26:32,067 The long-term fate of our universe 447 00:26:32,091 --> 00:26:35,960 will be sprinkled with all these glittering diamonds. 448 00:26:37,930 --> 00:26:41,376 A zombie that comes to life and shines like a diamond 449 00:26:41,400 --> 00:26:43,211 might be pretty to look at, 450 00:26:43,235 --> 00:26:47,338 but it's still no guarantee that life could survive here. 451 00:26:48,841 --> 00:26:51,820 You can kind of think of these white dwarfs 452 00:26:51,844 --> 00:26:55,457 as maybe making a little more energy for the universe, 453 00:26:55,481 --> 00:26:58,060 but even that's going to eventually run out. 454 00:26:58,084 --> 00:27:01,863 The whole thing becomes a gigantic crystal and, again, 455 00:27:01,887 --> 00:27:04,755 it's just going to start cooling and fading away. 456 00:27:05,891 --> 00:27:09,137 The zombie fizzles out into a dark cinder, 457 00:27:09,161 --> 00:27:12,941 giving off almost no light at all, 458 00:27:12,965 --> 00:27:17,401 but there's another monster lurking in the cosmos. 459 00:27:20,673 --> 00:27:23,785 When a star that's much more massive than the sun dies, 460 00:27:23,809 --> 00:27:24,987 it explodes violently, 461 00:27:25,011 --> 00:27:27,723 and during that explosion, the core collapses 462 00:27:27,747 --> 00:27:30,993 and becomes an incredibly dense, small object, 463 00:27:31,017 --> 00:27:35,419 one of the most wonderful real monsters in the universe. 464 00:27:37,123 --> 00:27:39,434 This is a pulsar... 465 00:27:39,458 --> 00:27:44,239 PSR B0329+54, 466 00:27:44,263 --> 00:27:47,342 3,000 light-years away from us. 467 00:27:47,366 --> 00:27:50,012 The pulsar has the mass of the sun, 468 00:27:50,036 --> 00:27:52,414 but is just 12 miles across. 469 00:27:52,438 --> 00:27:57,352 Its rapid spin generates beams of radiation from its poles, 470 00:27:57,376 --> 00:28:00,477 bringing the zombie to life. 471 00:28:01,714 --> 00:28:07,829 Now, we've discovered an alien world orbiting this zombie star. 472 00:28:07,853 --> 00:28:10,565 In 2017, a new planet 473 00:28:10,589 --> 00:28:12,868 was discovered around a pulsar. 474 00:28:12,892 --> 00:28:15,904 They're about twice the mass of the earth, 475 00:28:15,928 --> 00:28:18,407 and that's really incredible. 476 00:28:18,431 --> 00:28:21,677 The pulsar planet sounds intriguing, 477 00:28:21,701 --> 00:28:24,980 but the prospects for life aren't good. 478 00:28:25,004 --> 00:28:29,785 Orbiting a pulsar would be a brutal environment for life. 479 00:28:29,809 --> 00:28:32,721 It's highly unlikely that there's life 480 00:28:32,745 --> 00:28:35,924 because the radiation from this system would be overwhelming 481 00:28:35,948 --> 00:28:39,116 and likely blow away the atmosphere. 482 00:28:40,186 --> 00:28:42,798 As for sustaining life in the universe, 483 00:28:42,822 --> 00:28:47,135 none of these options is what you'd call a safe bet. 484 00:28:49,228 --> 00:28:52,774 These are momentary reprieves from the inevitable. 485 00:28:52,798 --> 00:28:55,010 No matter what you do, eventually, 486 00:28:55,034 --> 00:28:57,579 you're going to run out of these gimmes. 487 00:28:57,603 --> 00:29:00,382 You're going to run out of the get-of-jail-free cards. 488 00:29:00,406 --> 00:29:04,486 Inevitably, everything is going to cool and fade away. 489 00:29:07,246 --> 00:29:09,891 This might be game over for stars 490 00:29:09,915 --> 00:29:12,828 and even for life. 491 00:29:12,852 --> 00:29:17,599 But there is still a glimmer of hope hidden in the cosmos, 492 00:29:17,623 --> 00:29:20,769 a star that isn't dying. 493 00:29:20,793 --> 00:29:24,573 It appears blessed with eternal life, 494 00:29:24,597 --> 00:29:27,175 and its color is red. 495 00:29:27,199 --> 00:29:31,012 Red dwarfs... we are literally surrounded by them, 496 00:29:31,036 --> 00:29:33,237 but they are largely invisible to us. 497 00:29:46,685 --> 00:29:49,765 Illuminating every corner of our night sky 498 00:29:49,789 --> 00:29:52,934 is the light of stars... 499 00:29:52,958 --> 00:29:58,039 But what we see with a naked eye doesn't tell the whole story. 500 00:30:00,199 --> 00:30:03,345 The stars that you're seeing are mainly stars like the sun 501 00:30:03,369 --> 00:30:05,714 or even more massive and even hotter than the sun. 502 00:30:05,738 --> 00:30:08,617 They're bright. You can see them from a distance, 503 00:30:08,641 --> 00:30:11,286 but amazingly, the most common form of star, 504 00:30:11,310 --> 00:30:14,322 by far, are the red dwarf stars. 505 00:30:14,346 --> 00:30:16,491 They're up there right now in the sky, 506 00:30:16,515 --> 00:30:19,594 but they're just too small and too faint to see. 507 00:30:19,618 --> 00:30:23,365 Red dwarfs are up to 10 times smaller than the sun, 508 00:30:23,389 --> 00:30:26,101 and they burn less brightly. 509 00:30:26,125 --> 00:30:29,070 Right now, hidden in the night sky, 510 00:30:29,094 --> 00:30:33,542 over three-quarters of the stars in our galaxy are red dwarfs... 511 00:30:33,566 --> 00:30:38,313 And while the larger stars are dying out, 512 00:30:38,337 --> 00:30:41,316 we've never seen a red dwarf die, 513 00:30:41,340 --> 00:30:44,119 making them the best bet for life 514 00:30:44,143 --> 00:30:47,189 to survive the star apocalypse. 515 00:30:47,213 --> 00:30:51,293 When the most massive stars eventually go out 516 00:30:51,317 --> 00:30:54,129 and are not replaced, what will be left 517 00:30:54,153 --> 00:30:58,400 are much, much dimmer stars like red dwarf stars. 518 00:30:58,424 --> 00:31:01,903 We've seen star death across the universe, 519 00:31:01,927 --> 00:31:04,272 so why not red dwarfs? 520 00:31:04,296 --> 00:31:06,675 Turns out their size 521 00:31:06,699 --> 00:31:10,378 gives them a crucial advantage over larger stars. 522 00:31:10,402 --> 00:31:13,248 The more massive a star is, the hotter it burns. 523 00:31:13,272 --> 00:31:15,650 A red dwarf star burns at a lower temperature. 524 00:31:15,674 --> 00:31:17,552 So it doesn't burn through it's fuel 525 00:31:17,576 --> 00:31:19,688 quite as quickly as a mid-mass star does. 526 00:31:19,712 --> 00:31:22,691 These are like the economy cars of the universe. 527 00:31:22,715 --> 00:31:25,427 They're just sipping on their nuclear fuel, 528 00:31:25,451 --> 00:31:28,163 and they can coast along. 529 00:31:28,187 --> 00:31:31,333 Not only that, despite being smaller, 530 00:31:31,357 --> 00:31:34,057 they have access to more fuel. 531 00:31:35,327 --> 00:31:38,573 Our mid-size sun is split into three layers... 532 00:31:38,597 --> 00:31:41,309 a core, a radiation zone, 533 00:31:41,333 --> 00:31:43,478 and a convective layer. 534 00:31:43,502 --> 00:31:47,282 The radiation zone prevents hydrogen in the top layer 535 00:31:47,306 --> 00:31:50,685 from ever becoming available for the core to burn. 536 00:31:50,709 --> 00:31:52,954 So the sun can only access 537 00:31:52,978 --> 00:31:57,092 about 10 percent of its total hydrogen fuel. 538 00:31:57,116 --> 00:32:01,229 Once the hydrogen in our sun's core runs out, 539 00:32:01,253 --> 00:32:04,232 its days are numbered. 540 00:32:04,256 --> 00:32:06,468 In some ways, these mid-sized stars 541 00:32:06,492 --> 00:32:08,136 end up starving themselves. 542 00:32:08,160 --> 00:32:11,539 The smaller red dwarfs are different. 543 00:32:11,563 --> 00:32:15,043 They can access all the hydrogen they want. 544 00:32:15,067 --> 00:32:18,546 In low-mass stars, outside of the core, 545 00:32:18,570 --> 00:32:21,483 this outer layer is fully convective. 546 00:32:21,507 --> 00:32:25,353 What that means is, stuff near the core rises to the surface 547 00:32:25,377 --> 00:32:28,290 and then drops back down all the way to the core, 548 00:32:28,314 --> 00:32:30,492 and that means if you have hydrogen somewhere 549 00:32:30,516 --> 00:32:33,128 outside of the core, eventually, it's going to make 550 00:32:33,152 --> 00:32:35,597 its way down there, and it can be used for fuel. 551 00:32:35,621 --> 00:32:37,832 The red dwarf has access to everything 552 00:32:37,856 --> 00:32:39,167 at the all-you-can-eat buffet. 553 00:32:39,191 --> 00:32:41,736 It can grab stuff from the distant regions 554 00:32:41,760 --> 00:32:44,773 at the surface of the star and bring it all the way 555 00:32:44,797 --> 00:32:48,098 down the gullet to the heart of the star. 556 00:32:49,201 --> 00:32:52,414 This all-you-can-eat hydrogen buffet 557 00:32:52,438 --> 00:32:56,518 extends the life span of red dwarfs to incredible lengths. 558 00:32:56,542 --> 00:33:00,322 The universe is over 13 billion years old, 559 00:33:00,346 --> 00:33:04,114 but any red dwarf that age is a toddler. 560 00:33:05,517 --> 00:33:07,362 A red dwarf, even if it was born 561 00:33:07,386 --> 00:33:09,297 at the very beginning of the universe 562 00:33:09,321 --> 00:33:11,032 when red dwarfs could first form, 563 00:33:11,056 --> 00:33:14,703 even today, it's just a tiny fraction of its lifespan. 564 00:33:14,727 --> 00:33:17,272 They can last for trillions of years, 565 00:33:17,296 --> 00:33:20,542 thousands of times the current age of the universe. 566 00:33:20,566 --> 00:33:22,610 Thirteen billion years old... 567 00:33:22,634 --> 00:33:24,779 that seems like a long time, 568 00:33:24,803 --> 00:33:26,581 but a small red dwarf, 569 00:33:26,605 --> 00:33:28,783 it's barely out of diapers. 570 00:33:30,609 --> 00:33:33,021 Red dwarf stars will not die out 571 00:33:33,045 --> 00:33:36,558 for 10 trillion years or more... 572 00:33:36,582 --> 00:33:40,462 And we're discovering they have another trump card 573 00:33:40,486 --> 00:33:42,230 that's good news for life. 574 00:33:46,425 --> 00:33:48,737 February 2017. 575 00:33:48,761 --> 00:33:51,473 NASA announced the discovery of a system 576 00:33:51,497 --> 00:33:55,143 in the Aquarius constellation called Trappist-1 577 00:33:55,167 --> 00:34:00,570 where seven earth-sized planets orbit a red dwarf star. 578 00:34:01,707 --> 00:34:04,953 It turns out that red dwarfs, apparently, 579 00:34:04,977 --> 00:34:07,422 are really good at making planets, 580 00:34:07,446 --> 00:34:10,725 including planets that are roughly the size of the earth. 581 00:34:10,749 --> 00:34:16,164 That's really cool because these stars last a long time. 582 00:34:16,188 --> 00:34:18,666 If they have planets orbiting them with life, 583 00:34:18,690 --> 00:34:22,692 they could outlast our solar system by trillions of years. 584 00:34:23,762 --> 00:34:28,465 Sounds promising, but red dwarfs have an ugly side. 585 00:34:30,235 --> 00:34:32,547 In October 2018, 586 00:34:32,571 --> 00:34:35,283 astronomers turned the Hubble space telescope 587 00:34:35,307 --> 00:34:38,586 to a series of young red dwarf stars 588 00:34:38,610 --> 00:34:41,823 in the Tucana-Horologium association. 589 00:34:41,847 --> 00:34:47,829 They witnessed these infants throwing daily stellar tantrums. 590 00:34:47,853 --> 00:34:49,898 Even though they're the smallest stars, 591 00:34:49,922 --> 00:34:52,367 they actually have some of the strongest flares 592 00:34:52,391 --> 00:34:54,335 and storms on them. 593 00:34:54,359 --> 00:34:56,871 Red dwarfs can emit flares 594 00:34:56,895 --> 00:35:00,575 10,000 times more powerful than the sun. 595 00:35:00,599 --> 00:35:04,634 These flares would cook any nearby planets. 596 00:35:05,637 --> 00:35:07,348 When a red dwarf star forms, 597 00:35:07,372 --> 00:35:08,983 they're rotating very rapidly, 598 00:35:09,007 --> 00:35:11,386 and this creates a lot of magnetic activity 599 00:35:11,410 --> 00:35:14,556 which creates flares and mass ejections. 600 00:35:14,580 --> 00:35:16,925 For life to exist, 601 00:35:16,949 --> 00:35:21,251 it would have to wait for infant red dwarfs to grow up. 602 00:35:22,754 --> 00:35:24,799 As a red dwarf gets older, 603 00:35:24,823 --> 00:35:27,435 there's drag between the magnetic fields 604 00:35:27,459 --> 00:35:30,105 in space as it rotates, and that has the effect 605 00:35:30,129 --> 00:35:32,107 of slowing down its rate of rotation. 606 00:35:32,131 --> 00:35:34,409 And so this means the activity settles down. 607 00:35:34,433 --> 00:35:38,012 So maybe later, in this life of a red dwarf star, 608 00:35:38,036 --> 00:35:40,570 they can support planets with life. 609 00:35:42,908 --> 00:35:47,155 Red dwarf stars will dominate the future universe 610 00:35:47,179 --> 00:35:50,892 and may give life a chance to survive. 611 00:35:50,916 --> 00:35:55,096 These small red stars are extremely long-lived, 612 00:35:55,120 --> 00:35:57,732 but no star is immortal. 613 00:35:57,756 --> 00:36:01,302 Even though they're really going through their nuclear fuel 614 00:36:01,326 --> 00:36:06,329 very slowly, there's just not enough fuel to last forever. 615 00:36:07,599 --> 00:36:10,778 These little stars will die out eventually. 616 00:36:10,802 --> 00:36:16,084 Unlike their larger stellar siblings, they'll go quietly. 617 00:36:16,108 --> 00:36:18,219 Well, it actually just gets hotter, 618 00:36:18,243 --> 00:36:21,156 and the color of a star depends on its temperature. 619 00:36:21,180 --> 00:36:24,192 So as the red dwarf gets hotter, it turns bluer. 620 00:36:24,216 --> 00:36:27,128 So sometime in the very distant future, 621 00:36:27,152 --> 00:36:28,463 some of these red dwarfs 622 00:36:28,487 --> 00:36:31,232 are actually going to become blue dwarfs. 623 00:36:31,256 --> 00:36:35,703 The universe isn't old enough for blue dwarfs to exist yet. 624 00:36:35,727 --> 00:36:38,206 But trillions of years from now, 625 00:36:38,230 --> 00:36:43,133 a dim blue glow will complete the star apocalypse. 626 00:36:44,236 --> 00:36:48,183 There will be a last star, one last red dwarf, 627 00:36:48,207 --> 00:36:51,586 maybe now turning blue as it warms up, 628 00:36:51,610 --> 00:36:55,712 but it too will eventually cool off, fade away. 629 00:36:56,848 --> 00:36:59,394 And there will be no more stars in the universe. 630 00:36:59,418 --> 00:37:01,396 It is inevitable. 631 00:37:03,455 --> 00:37:06,534 In this dark, starless universe, 632 00:37:06,558 --> 00:37:09,804 prospects for life seem impossible. 633 00:37:09,828 --> 00:37:14,042 But will something else take the place of stars? 634 00:37:14,066 --> 00:37:16,678 As we get to the end of the universe, 635 00:37:16,702 --> 00:37:19,869 things get really cold, but they also get really weird. 636 00:37:35,854 --> 00:37:39,133 Trillions of years from now, the star apocalypse 637 00:37:39,157 --> 00:37:42,670 will leave the universe empty and dark, 638 00:37:42,694 --> 00:37:45,295 a never-ending night. 639 00:37:46,331 --> 00:37:47,942 The universe at this time 640 00:37:47,966 --> 00:37:49,844 is nothing like the universe of today. 641 00:37:49,868 --> 00:37:55,350 There's no light, and it's really cold and very lonely. 642 00:37:55,374 --> 00:37:59,187 When all of the stars die and the light goes away, 643 00:37:59,211 --> 00:38:01,189 anything that relies on the heat 644 00:38:01,213 --> 00:38:04,392 and the processes from these stars will start to die. 645 00:38:06,285 --> 00:38:08,563 Once all the lights go out, 646 00:38:08,587 --> 00:38:12,367 the only things that will remain will be the leftovers. 647 00:38:12,391 --> 00:38:15,169 With stars as we know them long gone, 648 00:38:15,193 --> 00:38:17,939 could something else spark into existence 649 00:38:17,963 --> 00:38:20,341 in this cosmic wasteland? 650 00:38:20,365 --> 00:38:23,278 You'd think that's it, no more star formation. 651 00:38:23,302 --> 00:38:27,181 But the universe still has a few tricks up its sleeve. 652 00:38:27,205 --> 00:38:29,851 Over the history of the universe, 653 00:38:29,875 --> 00:38:32,620 generations of stars have lived and died. 654 00:38:32,644 --> 00:38:36,090 They released heavy metal elements into the universe, 655 00:38:36,114 --> 00:38:39,727 building materials for a new kind of star, 656 00:38:39,751 --> 00:38:42,263 and stars born from these new materials 657 00:38:42,287 --> 00:38:46,801 can do things their ancestors could not. 658 00:38:46,825 --> 00:38:50,872 As you enrich the universe, as more and more metals 659 00:38:50,896 --> 00:38:52,607 get produced over time, 660 00:38:52,631 --> 00:38:56,311 you can lower the temperature needed 661 00:38:56,335 --> 00:38:58,913 for fusion reactions in a star. 662 00:38:58,937 --> 00:39:02,617 With lower temperatures needed for fusion, 663 00:39:02,641 --> 00:39:06,354 stars have become smaller and smaller. 664 00:39:06,378 --> 00:39:08,956 Currently, the smallest possible star 665 00:39:08,980 --> 00:39:11,626 is a little under 10 percent the sun's mass. 666 00:39:11,650 --> 00:39:14,062 But eventually it may be possible to form stars 667 00:39:14,086 --> 00:39:16,686 that have around 4 percent the sun's mass. 668 00:39:18,256 --> 00:39:21,703 Hundreds of trillions of years in the future, 669 00:39:21,727 --> 00:39:24,439 a new star may dominate the universe, 670 00:39:24,463 --> 00:39:30,545 built from scraps left over from generations of dead stars, 671 00:39:30,569 --> 00:39:32,647 a star so small 672 00:39:32,671 --> 00:39:36,039 that it burns cold instead of hot. 673 00:39:37,476 --> 00:39:39,320 One of the weirdest types of stars 674 00:39:39,344 --> 00:39:42,156 that scientists hypothesize might exist in the far future 675 00:39:42,180 --> 00:39:43,880 is the frozen star. 676 00:39:45,417 --> 00:39:49,564 You can start forming stars that are very, very small 677 00:39:49,588 --> 00:39:52,900 and very cold, where nuclear fusion 678 00:39:52,924 --> 00:39:57,472 is happening in the core, but the surfaces are cold. 679 00:40:00,832 --> 00:40:02,844 These small, cold objects 680 00:40:02,868 --> 00:40:04,946 will be thousands of times dimmer 681 00:40:04,970 --> 00:40:08,449 than the faintest star we see today. 682 00:40:08,473 --> 00:40:11,853 So cold, the temperatures on the surface 683 00:40:11,877 --> 00:40:15,456 could reach just 32 degrees Fahrenheit... 684 00:40:15,480 --> 00:40:19,761 And ice clouds may form in the star's atmosphere. 685 00:40:19,785 --> 00:40:23,398 They are so much cooler than stars now. 686 00:40:23,422 --> 00:40:27,902 They could actually have ice, water ice, on their surface, 687 00:40:27,926 --> 00:40:31,472 even though they are technically stars. 688 00:40:31,496 --> 00:40:36,077 It's literal water-ice covering the surface of a star, 689 00:40:36,101 --> 00:40:39,580 the same ice that you can use for ice-skating 690 00:40:39,604 --> 00:40:41,549 or ice racing or curling. 691 00:40:41,573 --> 00:40:43,284 You could do all of this 692 00:40:43,308 --> 00:40:46,476 on the surface of a star in the far future. 693 00:40:47,646 --> 00:40:50,024 It's hard to predict if life could arise 694 00:40:50,048 --> 00:40:53,316 on planets orbiting frozen stars. 695 00:40:55,454 --> 00:40:59,667 We won't know until one appears... 696 00:40:59,691 --> 00:41:03,827 And that won't be for a very long time. 697 00:41:05,497 --> 00:41:07,308 The universe is far too young 698 00:41:07,332 --> 00:41:09,610 for even the first one of these things 699 00:41:09,634 --> 00:41:11,446 to even be a glimmer of an idea. 700 00:41:11,470 --> 00:41:14,081 So if you want to wait, you know, a quadrillion years, 701 00:41:14,105 --> 00:41:15,917 then we can find out. 702 00:41:15,941 --> 00:41:18,753 Stars helped create us, 703 00:41:18,777 --> 00:41:21,055 building and spreading the ingredients 704 00:41:21,079 --> 00:41:23,124 for life to develop, 705 00:41:23,148 --> 00:41:25,159 but the coming star apocalypse 706 00:41:25,183 --> 00:41:27,829 may mean the end of life, 707 00:41:27,853 --> 00:41:30,186 just not for a while. 708 00:41:31,656 --> 00:41:36,337 Small red stars will continue to illuminate the darkness... 709 00:41:36,361 --> 00:41:41,042 Safe havens for life to survive and even flourish. 710 00:41:41,066 --> 00:41:42,777 As for us on earth, 711 00:41:42,801 --> 00:41:46,214 we should be most thankful for one star 712 00:41:46,238 --> 00:41:50,451 because without it, we simply wouldn't exist. 713 00:41:50,475 --> 00:41:53,621 I really want you to never experience a sunny day again 714 00:41:53,645 --> 00:41:54,989 and not think about this. 715 00:41:55,013 --> 00:41:57,358 The sun, someday, will burn out, 716 00:41:57,382 --> 00:41:59,527 and so will all of the other stars. 717 00:41:59,551 --> 00:42:03,598 We are in this wonderful era of light and warmth 718 00:42:03,622 --> 00:42:05,132 coming out of the sky, 719 00:42:05,156 --> 00:42:09,036 and everything is going to go dark, absolutely everything, 720 00:42:09,060 --> 00:42:11,138 everywhere in the universe. 721 00:42:11,162 --> 00:42:14,408 So for the time being, you know, enjoy the light. 722 00:42:14,432 --> 00:42:16,511 Step outside, enjoy the sun, 723 00:42:16,535 --> 00:42:19,647 and think about how lucky we are to live in this time. 58125

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