1 00:00:00,868 --> 00:00:04,436 ♪ 2 00:00:04,438 --> 00:00:09,408 narrator: Imagine a universe with no stars -- 3 00:00:09,410 --> 00:00:12,011 a dark, endless night. 4 00:00:14,081 --> 00:00:17,983 This is not some sci-fi nightmare. 5 00:00:17,985 --> 00:00:20,953 This is our future. 6 00:00:20,955 --> 00:00:24,690 There will definitely be a point in the future when, you look up, 7 00:00:24,692 --> 00:00:27,159 you will no longer be able to see stars. 8 00:00:27,161 --> 00:00:29,628 Thaller: Things really will get darker and darker, 9 00:00:29,630 --> 00:00:33,866 until there will be almost no memory of light left. 10 00:00:33,868 --> 00:00:39,038 Narrator: For billions of years, stars brought life to the universe. 11 00:00:39,040 --> 00:00:45,377 The fact that you exist at all is because of stars. 12 00:00:45,379 --> 00:00:50,716 Narrator: Now, they're dying out in a star apocalypse. 13 00:00:50,718 --> 00:00:53,118 Stricker: The effect could be tremendous. 14 00:00:53,120 --> 00:00:56,321 It can permeate throughout the universe. 15 00:00:56,323 --> 00:00:58,824 Narrator: What's causing the die-off, 16 00:00:58,826 --> 00:01:03,896 and what happens to life when the lights go out? 17 00:01:03,898 --> 00:01:06,165 Eventually, the whole entire universe 18 00:01:06,167 --> 00:01:09,368 starts to get a little bit weird. 19 00:01:15,543 --> 00:01:18,544 -- 00:02:27,880 narrator: May, 2018. 38 00:02:27,882 --> 00:02:30,916 Astronomers investigated j1228 39 00:02:30,918 --> 00:02:34,419 using the world's largest optical telescope -- 40 00:02:34,421 --> 00:02:38,490 the gran telescopio canarias. 41 00:02:38,492 --> 00:02:42,060 They discovered what appears to be a ball of iron 42 00:02:42,062 --> 00:02:44,663 orbiting the white dwarf. 43 00:02:44,665 --> 00:02:48,567 The lump of metal, less than 400 miles across, 44 00:02:48,569 --> 00:02:52,938 could be the exposed core of a destroyed planet. 45 00:02:52,940 --> 00:02:56,875 It's a clue to this system's past. 46 00:02:56,877 --> 00:02:58,243 Thaller: It's always a little poignant 47 00:02:58,245 --> 00:03:01,446 when you see evidence of a planet around a dead star. 48 00:03:01,448 --> 00:03:03,515 You know, you think back of when that star was shining, 49 00:03:03,517 --> 00:03:06,018 and could there have been life in that solar system? 50 00:03:06,020 --> 00:03:11,089 Narrator: The j1228 system is a cosmic graveyard. 51 00:03:11,091 --> 00:03:14,493 It might look different than our solar system, 52 00:03:14,495 --> 00:03:18,063 but this is our future. 53 00:03:18,065 --> 00:03:22,534 This discovery of a dead planet orbiting a dead star 54 00:03:22,536 --> 00:03:24,870 is like looking into a crystal ball. 55 00:03:24,872 --> 00:03:28,040 And is it the future of our own solar system? 56 00:03:28,042 --> 00:03:29,374 Yep. 57 00:03:29,376 --> 00:03:31,210 For a glimpse into your future, you know, 58 00:03:31,212 --> 00:03:33,278 all you need to do is look up. 59 00:03:37,484 --> 00:03:42,754 Narrator: Just like j1228, our sun will die, 60 00:03:42,756 --> 00:03:46,024 killing off earth in the process. 61 00:03:46,026 --> 00:03:50,262 This terrifying fate will play out across the galaxy 62 00:03:50,264 --> 00:03:53,365 in a star apocalypse. 63 00:03:53,367 --> 00:03:56,802 Our sun is a fairly common type of star in the milky way, 64 00:03:56,804 --> 00:03:59,338 and so, other stars in the milky way 65 00:03:59,340 --> 00:04:01,573 will undergo the same sort of fate as the sun. 66 00:04:01,575 --> 00:04:03,108 They will end up as white dwarfs. 67 00:04:03,110 --> 00:04:06,245 And so, any other planets out there orbiting sun-like stars 68 00:04:06,247 --> 00:04:08,046 will undergo a similar fate. 69 00:04:10,951 --> 00:04:13,018 Once the stars like our sun have died out, 70 00:04:13,020 --> 00:04:14,186 what's gonna happen? 71 00:04:14,188 --> 00:04:18,624 Could life still survive around white dwarfs? 72 00:04:18,626 --> 00:04:21,526 Narrator: To understand the fate of sun-like stars, 73 00:04:21,528 --> 00:04:23,362 we have to look inside them. 74 00:04:23,364 --> 00:04:28,600 Buried within are clues to how they live, and why they die. 75 00:04:28,602 --> 00:04:31,436 Plait: The core, the very center, that's where the action is. 76 00:04:31,438 --> 00:04:34,506 That's where the star is fusing light elements 77 00:04:34,508 --> 00:04:36,708 into heavier elements. 78 00:04:36,710 --> 00:04:38,343 And that works like a hydrogen bomb. 79 00:04:38,345 --> 00:04:39,978 It's the same thing. 80 00:04:39,980 --> 00:04:43,215 If you compress hydrogen enough, it gets very hot, 81 00:04:43,217 --> 00:04:44,850 and the pressure gets very high, 82 00:04:44,852 --> 00:04:49,054 and if fuses into helium, and generates energy -- heat. 83 00:04:49,056 --> 00:04:52,457 And that's what's happening in the core of every star. 84 00:04:52,459 --> 00:04:54,293 Narrator: Because of their enormous mass, 85 00:04:54,295 --> 00:04:57,529 stars have huge amounts of gravity. 86 00:04:57,531 --> 00:05:02,768 This gravity pushes inwards, trying to collapse the star, 87 00:05:02,770 --> 00:05:07,973 but fusion energy from the core stops that from happening. 88 00:05:07,975 --> 00:05:11,076 It's really this sort of very balanced dance 89 00:05:11,078 --> 00:05:14,880 between gravity pushing in, fusion energy pushing out. 90 00:05:14,882 --> 00:05:18,984 You can think of a star as losing energy, 91 00:05:18,986 --> 00:05:20,786 continuously, to the outside world/ 92 00:05:20,788 --> 00:05:23,388 and gravity is saying, "yes, I'm gonna take over." 93 00:05:23,390 --> 00:05:27,659 but, no, the nuclear reactions inside a star 94 00:05:27,661 --> 00:05:30,429 replenish the energy that's lost, 95 00:05:30,431 --> 00:05:33,965 and keep the star hot and pressurized inside, 96 00:05:33,967 --> 00:05:40,238 so that the pressure-gravity balance can be maintained. 97 00:05:40,240 --> 00:05:43,675 Narrator: This balance keeps sun-like stars alive 98 00:05:43,677 --> 00:05:46,845 for up to 10 billion years, 99 00:05:46,847 --> 00:05:51,683 until the star's gas tank runs dry. 100 00:05:51,685 --> 00:05:53,418 Plait: It's gonna run out of fuel. 101 00:05:53,420 --> 00:05:56,154 And when that happens, it's going to die. 102 00:05:56,156 --> 00:05:57,389 But what is that gonna look like? 103 00:05:57,391 --> 00:05:59,024 How is this gonna happen? 104 00:06:00,894 --> 00:06:02,761 Narrator: One hundred million years ago, 105 00:06:02,763 --> 00:06:08,800 things in the j1228 system started to get ugly. 106 00:06:08,802 --> 00:06:14,406 First, the star grew large -- really large. 107 00:06:14,408 --> 00:06:17,509 Straughn: Once the center starts fusing heavier elements, 108 00:06:17,511 --> 00:06:19,044 the outside will swell 109 00:06:19,046 --> 00:06:22,848 into what will eventually be a red giant star. 110 00:06:22,850 --> 00:06:28,153 Narrator: J1228 transformed into a red giant. 111 00:06:28,155 --> 00:06:29,821 Its outer layers blew off, 112 00:06:29,823 --> 00:06:34,526 extending out over 40 million miles. 113 00:06:34,528 --> 00:06:37,963 When stars like our sun die, it's not a quiet affair. 114 00:06:37,965 --> 00:06:41,099 It's very violent, and ugly, and messy. 115 00:06:41,101 --> 00:06:42,768 They turn into red giants, 116 00:06:42,770 --> 00:06:45,003 and they turn themselves inside out, 117 00:06:45,005 --> 00:06:49,174 and vomit all over the solar system. 118 00:06:49,176 --> 00:06:52,778 Narrator: When j1228 swelled into a red giant, 119 00:06:52,780 --> 00:06:58,283 nearby planets were stuck in a kill zone. 120 00:06:58,285 --> 00:07:01,787 The dying star engulfed them, or fried them 121 00:07:01,789 --> 00:07:05,657 with temperatures of over 1,200 degrees fahrenheit. 122 00:07:05,659 --> 00:07:08,360 Atmospheres disappeared. 123 00:07:08,362 --> 00:07:10,962 Oceans boiled away, 124 00:07:10,964 --> 00:07:15,700 but one planet survived j1228's death throes. 125 00:07:15,702 --> 00:07:20,372 Here's a case where a planet survived, in some sense, 126 00:07:20,374 --> 00:07:23,675 the death of its own star, and it's still hanging around, 127 00:07:23,677 --> 00:07:28,013 still hanging on, hoping for something new. 128 00:07:28,015 --> 00:07:30,449 Narrator: The red giant's expanding outer layers 129 00:07:30,451 --> 00:07:32,951 separated from the star's core. 130 00:07:34,955 --> 00:07:41,760 With no active fusion, the core collapsed into a white dwarf. 131 00:07:41,762 --> 00:07:43,829 The white dwarf's dense gravity 132 00:07:43,831 --> 00:07:48,433 then went to work on the one surviving planet. 133 00:07:48,435 --> 00:07:52,003 Flippenko: The planet that might've been orbiting the normal star 134 00:07:52,005 --> 00:07:55,774 can gradually spiral in toward the white dwarf, 135 00:07:55,776 --> 00:07:58,777 and then, eventually, the gravity of the white dwarf pulls 136 00:07:58,779 --> 00:08:02,180 on the near side of the planet more than on the far side, 137 00:08:02,182 --> 00:08:04,483 and that tears it apart. 138 00:08:04,485 --> 00:08:07,085 Plait: What we're seeing here is a dead star 139 00:08:07,087 --> 00:08:10,188 dining on its own solar system. 140 00:08:11,925 --> 00:08:14,993 That's what is in the future for the sun. 141 00:08:17,998 --> 00:08:23,168 Narrator: J1228 feasted on the remains of its rocky worlds, 142 00:08:23,170 --> 00:08:29,508 leaving behind a disk of debris and the planetary core. 143 00:08:29,510 --> 00:08:33,612 It's a glimpse of earth's future. 144 00:08:33,614 --> 00:08:35,914 What happened here around this white dwarf 145 00:08:35,916 --> 00:08:37,249 is gonna happen to earth. 146 00:08:37,251 --> 00:08:39,618 It's gonna be stripped of its atmosphere, 147 00:08:39,620 --> 00:08:41,753 its crust, and its mantle, 148 00:08:41,755 --> 00:08:46,491 and the only thing that will remain will be the core. 149 00:08:46,493 --> 00:08:49,661 Narrator: Fried and ripped apart by a dying star -- 150 00:08:49,663 --> 00:08:52,197 not a good way to go. 151 00:08:52,199 --> 00:08:54,332 Fortunately, for life on earth, 152 00:08:54,334 --> 00:08:58,036 our own sun isn't dying just yet. 153 00:08:58,038 --> 00:08:59,871 Plait: The sun is middle-aged. 154 00:08:59,873 --> 00:09:01,540 It's 4.5 billion years old, 155 00:09:01,542 --> 00:09:04,843 and it's going to go on for another 5 or 6 billion years. 156 00:09:04,845 --> 00:09:06,378 Sutter: We've got a little bit of time 157 00:09:06,380 --> 00:09:11,116 before our sun pukes all over the solar system. 158 00:09:11,118 --> 00:09:13,618 Narrator: Our home planet may be safe for now, 159 00:09:13,620 --> 00:09:16,755 but systems like j1228 show us 160 00:09:16,757 --> 00:09:20,892 that sun-like stars are destined to die, 161 00:09:20,894 --> 00:09:24,729 killing off any life orbiting them. 162 00:09:24,731 --> 00:09:27,933 But sun-like stars aren't the only stars 163 00:09:27,935 --> 00:09:30,468 dying across the cosmos. 164 00:09:30,470 --> 00:09:35,307 There are others out there, and they're all doomed. 165 00:09:35,309 --> 00:09:38,376 There's a wonderful rainbow of stars 166 00:09:38,378 --> 00:09:40,178 out there, of all different shapes, 167 00:09:40,180 --> 00:09:43,181 all different sizes, and all different colors. 168 00:09:43,183 --> 00:09:44,916 Straughn: We're talking down to, you know, 169 00:09:44,918 --> 00:09:46,818 fractions of the mass of the sun, 170 00:09:46,820 --> 00:09:50,055 up to hundreds of times the mass of the sun. 171 00:09:50,057 --> 00:09:53,959 Narrator: When it comes to the star apocalypse, size matters. 172 00:09:53,961 --> 00:09:57,862 The bigger and brighter the star, the faster it dies. 173 00:10:12,913 --> 00:10:17,515 ♪ 174 00:10:17,517 --> 00:10:21,786 narrator: Our universe is a vast expanse of death and destruction. 175 00:10:23,924 --> 00:10:29,327 All of the stars are destined to die, but not all at once. 176 00:10:30,964 --> 00:10:33,198 There's not going to be one particular point 177 00:10:33,200 --> 00:10:35,867 where all the lights turn off at the same time. 178 00:10:35,869 --> 00:10:38,503 It's more like a power outage, 179 00:10:38,505 --> 00:10:42,107 where different grids go off at different times, until, 180 00:10:42,109 --> 00:10:46,478 like, there's the one last light bulb that'll just go off. 181 00:10:46,480 --> 00:10:51,483 Narrator: This is because stars come in different sizes. 182 00:10:51,485 --> 00:10:53,952 The way a star dies has everything to do with 183 00:10:53,954 --> 00:10:55,920 the amount of mass it started life with. 184 00:10:55,922 --> 00:10:59,791 It carries that all the way through its lifetime. 185 00:10:59,793 --> 00:11:02,694 Narrator: The sun is a medium-sized star 186 00:11:02,696 --> 00:11:06,931 living a stable existence for billions of years. 187 00:11:06,933 --> 00:11:09,768 Giant stars are different. 188 00:11:09,770 --> 00:11:13,571 They live fast, and die young. 189 00:11:13,573 --> 00:11:17,242 A star like the sun, which is a medium-sized star, 190 00:11:17,244 --> 00:11:19,678 it lives about 10 billion years. 191 00:11:19,680 --> 00:11:21,479 The really massive stars, 192 00:11:21,481 --> 00:11:25,350 they live maybe 10 million years. 193 00:11:25,352 --> 00:11:28,753 Narrator: Massive stars can be tens or even hundreds of times 194 00:11:28,755 --> 00:11:31,756 more massive than the sun. 195 00:11:31,758 --> 00:11:35,927 When it comes to life span, that's a problem. 196 00:11:35,929 --> 00:11:40,765 Flippenko: A massive star has more fuel to burn, in a nuclear sense. 197 00:11:40,767 --> 00:11:43,468 So, you might naively think that it lasts longer, 198 00:11:43,470 --> 00:11:45,970 but it's the exact opposite. 199 00:11:45,972 --> 00:11:51,543 Narrator: Massive stars can only access hydrogen fuel in their core. 200 00:11:51,545 --> 00:11:54,512 The rest is trapped in the outer layers, 201 00:11:54,514 --> 00:11:57,415 and can't be used as fuel. 202 00:11:57,417 --> 00:11:59,751 Plait: If there's hydrogen in the core, you're good. 203 00:11:59,753 --> 00:12:03,221 If there's hydrogen outside of the core, it can't be used. 204 00:12:03,223 --> 00:12:06,357 If it's not in your fuel tank, it's not doing you any good. 205 00:12:07,994 --> 00:12:13,665 Narrator: Massive stars also have more gravity than smaller stars, 206 00:12:13,667 --> 00:12:17,435 so they have to burn their hydrogen fuel faster 207 00:12:17,437 --> 00:12:19,704 to prevent the star from collapsing. 208 00:12:21,708 --> 00:12:23,808 They burn their candle on both ends. 209 00:12:23,810 --> 00:12:25,710 Because of their incredible mass, 210 00:12:25,712 --> 00:12:27,812 their fusion reactions in the core 211 00:12:27,814 --> 00:12:30,348 happen at an incredible rate. 212 00:12:30,350 --> 00:12:32,951 Stricker: Giant stars are kind of fast and furious. 213 00:12:32,953 --> 00:12:34,719 They are bright. 214 00:12:34,721 --> 00:12:37,856 They live their life, and they die very quickly. 215 00:12:40,026 --> 00:12:42,627 Narrator: When a giant star's fuel runs out, 216 00:12:42,629 --> 00:12:44,929 the core collapses catastrophically 217 00:12:44,931 --> 00:12:48,399 under the overwhelming force of gravity. 218 00:12:48,401 --> 00:12:51,536 And then, boom, supernova. 219 00:12:58,512 --> 00:13:00,211 Narrator: The death of a giant star 220 00:13:00,213 --> 00:13:03,081 triggers one of the biggest bangs in the universe. 221 00:13:07,220 --> 00:13:11,156 The blast would instantly vaporize nearby planets. 222 00:13:14,995 --> 00:13:19,898 But these star deaths are also critical for life. 223 00:13:19,900 --> 00:13:22,934 When massive stars die, they release heavy elements 224 00:13:22,936 --> 00:13:25,904 they've been making through the course of their lives. 225 00:13:25,906 --> 00:13:27,906 And sometimes, they even make new ones. 226 00:13:27,908 --> 00:13:32,944 And it's these heavier elements that are essential for life. 227 00:13:32,946 --> 00:13:35,480 We owe our existence to stars 228 00:13:35,482 --> 00:13:38,316 that formed billions of years ago. 229 00:13:42,789 --> 00:13:47,892 Narrator: In may of 2018, we spotted evidence of ancient stars 230 00:13:47,894 --> 00:13:50,395 creating the stuff of life. 231 00:13:50,397 --> 00:13:53,031 We picked up an infrared light signal 232 00:13:53,033 --> 00:13:59,304 from a distant galaxy named macs1149-jd1. 233 00:14:01,141 --> 00:14:04,142 The signal was ionized oxygen. 234 00:14:06,613 --> 00:14:10,481 It's been traveling for 13.3 billion years, 235 00:14:10,483 --> 00:14:15,119 so the oxygen formed when the universe was very young -- 236 00:14:15,121 --> 00:14:20,792 just 500 million years after the big bang. 237 00:14:20,794 --> 00:14:26,731 This oxygen formed in the hearts of massive stars. 238 00:14:26,733 --> 00:14:28,299 Hopkins: The presence of oxygen tells us 239 00:14:28,301 --> 00:14:31,603 that there needed to be massive stars in the early universe 240 00:14:31,605 --> 00:14:34,038 in order to synthesize hydrogen and helium 241 00:14:34,040 --> 00:14:36,374 into heavier elements, like oxygen, 242 00:14:36,376 --> 00:14:39,010 and then explode to eject that oxygen 243 00:14:39,012 --> 00:14:42,814 back into the interstellar and intergalactic medium. 244 00:14:44,918 --> 00:14:49,220 Narrator: Extreme pressure in the cores of the stars produces oxygen... 245 00:14:51,524 --> 00:14:55,927 ...And other elements, like carbon and nitrogen. 246 00:14:55,929 --> 00:15:00,164 Supernova blasts spread these elements across the universe, 247 00:15:00,166 --> 00:15:04,535 helping to create new generations of stars, 248 00:15:04,537 --> 00:15:08,806 and, most importantly, us. 249 00:15:08,808 --> 00:15:11,809 If there is one single fact that you should care about 250 00:15:11,811 --> 00:15:15,413 in all of science -- and this is my favorite fact -- 251 00:15:15,415 --> 00:15:18,683 is that you and I are a consequence of star death. 252 00:15:22,455 --> 00:15:24,422 Bullock: Before you can have life, you need to have 253 00:15:24,424 --> 00:15:27,325 the kind of elements out of which life forms. 254 00:15:27,327 --> 00:15:29,294 You need carbon. You need nitrogen. 255 00:15:29,296 --> 00:15:30,662 You need oxygen. 256 00:15:30,664 --> 00:15:32,530 You need the elements that are the backbone 257 00:15:32,532 --> 00:15:36,134 to the biology that makes us possible. 258 00:15:36,136 --> 00:15:37,602 Where did those elements come from? 259 00:15:37,604 --> 00:15:38,903 Well, they came from stars. 260 00:15:38,905 --> 00:15:41,372 They came from stars that formed in the early universe, 261 00:15:41,374 --> 00:15:44,175 before even the sun existed. 262 00:15:44,177 --> 00:15:46,577 Narrator: The huge size of massive stars 263 00:15:46,579 --> 00:15:49,547 quickly signs their death warrants. 264 00:15:49,549 --> 00:15:56,020 Their explosive ends help create new stars, and even life. 265 00:15:56,022 --> 00:16:01,225 The fact that you exist at all is because of stars. 266 00:16:02,562 --> 00:16:05,830 Narrator: But, probing galaxies across the universe, 267 00:16:05,832 --> 00:16:08,499 we've discovered something else. 268 00:16:08,501 --> 00:16:12,403 The star apocalypse isn't just killing stars. 269 00:16:12,405 --> 00:16:15,773 It's stopping them from ever being born. 270 00:16:15,775 --> 00:16:17,508 Thaller: Star formation is dying. 271 00:16:17,510 --> 00:16:19,978 And in fact, it's dying rather quickly. 272 00:16:19,980 --> 00:16:22,080 The universe, right before our eyes, 273 00:16:22,082 --> 00:16:24,115 is becoming a darker place. 274 00:16:24,117 --> 00:16:25,850 It's running out of fuel. 275 00:16:25,852 --> 00:16:29,153 And eventually, no more stars will be made at all. 276 00:16:43,069 --> 00:16:46,804 ♪ 277 00:16:46,806 --> 00:16:51,042 ♪ 278 00:16:51,044 --> 00:16:55,513 narrator: Life on earth follows a series of regular patterns. 279 00:16:55,515 --> 00:16:59,150 Day after day, the sun rises... 280 00:16:59,152 --> 00:17:02,220 And sets, 281 00:17:02,222 --> 00:17:06,924 and stars light up the darkness of the night sky. 282 00:17:06,926 --> 00:17:09,894 The reason I got into astronomy to begin with 283 00:17:09,896 --> 00:17:12,363 was because I grew up in a rural part of the country, 284 00:17:12,365 --> 00:17:13,831 and the sky was beautiful and dark. 285 00:17:13,833 --> 00:17:15,633 You go outside at night, and you look up, 286 00:17:15,635 --> 00:17:18,403 and you could see thousands of stars. 287 00:17:18,405 --> 00:17:20,805 But it won't be that way forever. 288 00:17:23,309 --> 00:17:27,779 Narrator: 2016, a network of telescopes across the world 289 00:17:27,781 --> 00:17:32,517 measured the energy outputs of over 200,000 galaxies. 290 00:17:32,519 --> 00:17:34,519 ♪ 291 00:17:34,521 --> 00:17:37,588 they discovered that in the past 2 billion years, 292 00:17:37,590 --> 00:17:40,958 the universe has lost half its brightness. 293 00:17:42,429 --> 00:17:44,929 The night sky is getting darker 294 00:17:44,931 --> 00:17:49,233 as stars flicker out of existence. 295 00:17:49,235 --> 00:17:50,768 About 10 billion years ago, 296 00:17:50,770 --> 00:17:52,837 the universe kind of hit its peak, 297 00:17:52,839 --> 00:17:55,273 and lots of stars were shining. 298 00:17:55,275 --> 00:17:58,209 It was an incredibly bright place, 299 00:17:58,211 --> 00:18:00,778 but in the last couple billion years, 300 00:18:00,780 --> 00:18:04,615 it's really, overall, become a less bright place. 301 00:18:04,617 --> 00:18:07,485 The darkening universe isn't just a sign 302 00:18:07,487 --> 00:18:09,921 that stars are dying. 303 00:18:09,923 --> 00:18:15,460 It seems there's a problem with star birth as well. 304 00:18:15,462 --> 00:18:17,595 Mingarelli: When we look into the universe's past, 305 00:18:17,597 --> 00:18:19,197 what we find is that long ago, 306 00:18:19,199 --> 00:18:21,799 stars were forming at a much higher rate. 307 00:18:21,801 --> 00:18:24,168 Right now what we see is that really, 308 00:18:24,170 --> 00:18:27,972 stars are dying off faster than they're being born. 309 00:18:27,974 --> 00:18:30,374 A milky way-type galaxy, today, 310 00:18:30,376 --> 00:18:32,810 produces about seven stars per year. 311 00:18:32,812 --> 00:18:35,313 However, 11 billion years ago, 312 00:18:35,315 --> 00:18:38,850 a galaxy like our own would've produced 10 times more stars. 313 00:18:40,453 --> 00:18:43,321 Narrator: In the early universe, old stars died, 314 00:18:43,323 --> 00:18:46,290 and new ones formed in their place 315 00:18:46,292 --> 00:18:48,526 from the material left over. 316 00:18:48,528 --> 00:18:51,696 It was a cycle that kept the cosmos bright. 317 00:18:52,665 --> 00:18:54,799 Not anymore. 318 00:18:54,801 --> 00:18:58,803 Plait: It kind of sucks for us. We like a bright universe. 319 00:18:58,805 --> 00:19:01,405 We like all this energy and life 320 00:19:01,407 --> 00:19:03,741 that's vibrating through the universe, 321 00:19:03,743 --> 00:19:06,611 but that's just not always going to be the case. 322 00:19:06,613 --> 00:19:09,914 The universe is already winding down. 323 00:19:09,916 --> 00:19:12,483 ♪ 324 00:19:12,485 --> 00:19:15,653 straughn: One of the biggest mysteries in galaxy evolution 325 00:19:15,655 --> 00:19:18,990 is figuring out how galaxies stop forming their stars. 326 00:19:18,992 --> 00:19:21,092 And we really don't know the answer yet, 327 00:19:21,094 --> 00:19:23,594 and it's really important for us to figure out why 328 00:19:23,596 --> 00:19:27,365 because in the end, stars really equal life. 329 00:19:27,367 --> 00:19:29,967 ♪ 330 00:19:29,969 --> 00:19:33,137 narrator: To find out what is shutting off the stars, 331 00:19:33,139 --> 00:19:35,773 we study galaxy clusters. 332 00:19:35,775 --> 00:19:38,976 ♪ 333 00:19:38,978 --> 00:19:41,112 these giant regions of space 334 00:19:41,114 --> 00:19:45,816 contain hundreds of galaxies bound together by gravity. 335 00:19:46,953 --> 00:19:51,255 Slowly, the clusters pull new galaxies into them, 336 00:19:51,257 --> 00:19:55,526 causing something strange to happen. 337 00:19:55,528 --> 00:19:59,430 What we see happening when a galaxy falls into a cluster 338 00:19:59,432 --> 00:20:01,365 is that its star formation is quenched. 339 00:20:01,367 --> 00:20:03,734 It's shut off. 340 00:20:03,736 --> 00:20:06,237 Narrator: The cause of this quenching effect 341 00:20:06,239 --> 00:20:10,007 has baffled scientists for decades. 342 00:20:10,009 --> 00:20:13,244 Then in October of 2018, 343 00:20:13,246 --> 00:20:15,880 an international team of astronomers 344 00:20:15,882 --> 00:20:18,783 investigated this long-standing mystery. 345 00:20:18,785 --> 00:20:20,651 ♪ 346 00:20:20,653 --> 00:20:23,387 they tracked variations in quenching 347 00:20:23,389 --> 00:20:25,156 across 14 galaxy clusters 348 00:20:25,158 --> 00:20:29,126 and found a possible explanation. 349 00:20:29,128 --> 00:20:32,063 Thaller: The ability a galaxy has to make new stars 350 00:20:32,065 --> 00:20:35,399 is related to the larger environment it finds itself in. 351 00:20:35,401 --> 00:20:38,169 In clusters of galaxies where many galaxies 352 00:20:38,171 --> 00:20:39,770 are orbiting around each other, 353 00:20:39,772 --> 00:20:44,709 we see interactions that strip gas and dust away from galaxies. 354 00:20:44,711 --> 00:20:46,577 The stuff that makes up stars 355 00:20:46,579 --> 00:20:49,046 literally just thrown off into space. 356 00:20:50,917 --> 00:20:54,385 Narrator: Stars formed from dense parcels of cold gas, 357 00:20:54,387 --> 00:20:56,254 something galaxies are filled with. 358 00:20:58,091 --> 00:21:01,092 But when a galaxy is dragged into a cluster, 359 00:21:01,094 --> 00:21:03,427 everything changes. 360 00:21:03,429 --> 00:21:06,697 Clusters of galaxies contain a lot of hot gas, 361 00:21:06,699 --> 00:21:09,267 whereas you need cold gas inside of a galaxy 362 00:21:09,269 --> 00:21:10,901 in order to form stars, 363 00:21:10,903 --> 00:21:14,171 and when a galaxy is moving through this hot gas, 364 00:21:14,173 --> 00:21:17,742 then the cold gas inside is stripped away. 365 00:21:19,178 --> 00:21:20,911 Narrator: If this new study is right, 366 00:21:20,913 --> 00:21:25,182 and galaxy clusters are stripping away star-forming gas, 367 00:21:25,184 --> 00:21:28,486 new starlight will become rare. 368 00:21:29,656 --> 00:21:32,056 Looking over the history of the universe 369 00:21:32,058 --> 00:21:35,359 and how much gas was out there and how much is still left, 370 00:21:35,361 --> 00:21:38,195 I think it's fair to say that most of the stars 371 00:21:38,197 --> 00:21:41,299 that will ever be made already have been made. 372 00:21:41,301 --> 00:21:43,100 They've already been born. 373 00:21:44,504 --> 00:21:47,338 Narrator: Thanks to the shortage of star-forming gas, 374 00:21:47,340 --> 00:21:50,975 stars won't just be dying in the universe. 375 00:21:50,977 --> 00:21:52,977 They'll go extinct, 376 00:21:52,979 --> 00:21:56,814 and the first to go will be the largest. 377 00:21:56,816 --> 00:21:59,016 Plait: As the universe runs out of gas 378 00:21:59,018 --> 00:22:01,218 and fewer of these stars are being made, 379 00:22:01,220 --> 00:22:03,387 eventually sometime in the future, 380 00:22:03,389 --> 00:22:06,657 all the high-mass and even medium-mass stars like the sun, 381 00:22:06,659 --> 00:22:08,159 they'll be gone. 382 00:22:08,161 --> 00:22:10,628 What does that mean for life? 383 00:22:10,630 --> 00:22:13,798 ♪ 384 00:22:13,800 --> 00:22:16,067 narrator: Some of the brightest stars 385 00:22:16,069 --> 00:22:17,468 will disappear forever, 386 00:22:17,470 --> 00:22:20,571 begging the question, can life survive 387 00:22:20,573 --> 00:22:23,874 the monsters that dead stars leave behind? 388 00:22:24,911 --> 00:22:29,980 The long-term fate of the universe is not a pretty sight. 389 00:22:29,982 --> 00:22:34,285 Some very interesting creatures can start to appear. 390 00:22:34,287 --> 00:22:37,922 ♪ 391 00:22:48,935 --> 00:22:50,868 ♪ 392 00:22:50,870 --> 00:22:52,636 narrator: In the star apocalypse, 393 00:22:52,638 --> 00:22:56,040 the first stars to fade away will be the brightest -- 394 00:22:56,042 --> 00:23:01,679 the giant stars, followed by the mid-sized suns. 395 00:23:02,849 --> 00:23:07,218 The universe will become unrecognizable. 396 00:23:07,220 --> 00:23:09,854 The far future will be a very dim universe, 397 00:23:09,856 --> 00:23:11,956 especially for creatures like us. 398 00:23:11,958 --> 00:23:16,093 If there's no more gas, no more new stars, it gets dark. 399 00:23:17,630 --> 00:23:19,130 Narrator: Scared of the dark? 400 00:23:19,132 --> 00:23:21,665 You will be... 401 00:23:21,667 --> 00:23:24,135 Because 100 billion years from now, 402 00:23:24,137 --> 00:23:27,238 in the shadows of this new universe, 403 00:23:27,240 --> 00:23:30,508 monsters will come out to play. 404 00:23:30,510 --> 00:23:34,245 Now we find ourselves in the era of stars and starlight. 405 00:23:34,247 --> 00:23:36,313 What comes after you can think of 406 00:23:36,315 --> 00:23:38,916 as the era of the dead corpses of old stars. 407 00:23:40,420 --> 00:23:43,154 Narrator: We already see the corpses of dead stars 408 00:23:43,156 --> 00:23:46,257 scattered throughout the cosmos -- 409 00:23:46,259 --> 00:23:52,129 black holes, pulsars, white dwarfs. 410 00:23:52,131 --> 00:23:57,735 What happens when more stars die out and the dead take over? 411 00:23:57,737 --> 00:24:00,004 Can life survive? 412 00:24:00,006 --> 00:24:03,407 Thaller: It's actually possible that life in the universe will survive, 413 00:24:03,409 --> 00:24:05,576 but we're going to have to get more creative. 414 00:24:06,913 --> 00:24:09,980 Narrator: January 2019. 415 00:24:09,982 --> 00:24:14,852 The gaia satellite studied 15,000 white dwarfs 416 00:24:14,854 --> 00:24:18,088 within 300 light-years of earth. 417 00:24:18,090 --> 00:24:22,593 These are the corpses of sunlight stars. 418 00:24:22,595 --> 00:24:25,162 Plait: White dwarfs are the remnants, the cores, 419 00:24:25,164 --> 00:24:27,264 of stars like the sun after they die. 420 00:24:27,266 --> 00:24:30,234 There's no more fusion going on inside of a white dwarf. 421 00:24:30,236 --> 00:24:32,803 So it's just kind of sitting there cooling off, 422 00:24:32,805 --> 00:24:36,240 but it turns out there's a slight reprieve. 423 00:24:37,543 --> 00:24:41,512 Narrator: The white dwarf corpses usually cool off and dim 424 00:24:41,514 --> 00:24:44,114 over tens of billions of years. 425 00:24:44,116 --> 00:24:47,618 Gaia's data showed something different, 426 00:24:47,620 --> 00:24:50,621 something we've never seen before. 427 00:24:50,623 --> 00:24:54,558 Some of the older dead stars aren't dimming at all. 428 00:24:56,395 --> 00:24:57,895 O'dowd: We used to think that white dwarfs 429 00:24:57,897 --> 00:24:59,763 could really only dim over time. 430 00:24:59,765 --> 00:25:02,233 After all, there's no source of fusion, 431 00:25:02,235 --> 00:25:04,668 no source of energy in their interiors, 432 00:25:04,670 --> 00:25:07,972 but new studies with the gaia satellite have shown 433 00:25:07,974 --> 00:25:10,908 that there must be some other energy source 434 00:25:10,910 --> 00:25:14,078 keeping those older white dwarfs shining bright. 435 00:25:14,080 --> 00:25:16,080 ♪ 436 00:25:16,082 --> 00:25:19,850 something is giving these white dwarf corpses a spark, 437 00:25:19,852 --> 00:25:24,421 bringing them back from the dead as zombies. 438 00:25:24,423 --> 00:25:25,789 The leading contender 439 00:25:25,791 --> 00:25:28,592 is that the insides of white dwarfs 440 00:25:28,594 --> 00:25:30,794 actually crystallize. 441 00:25:32,331 --> 00:25:35,199 Narrator: Up to 6 billion years after dying, 442 00:25:35,201 --> 00:25:38,903 the hot carbon and oxygen matter inside the white dwarf 443 00:25:38,905 --> 00:25:42,773 cools and crystallizes, becoming solid, 444 00:25:42,775 --> 00:25:46,443 giving the dead star a lifeline. 445 00:25:46,445 --> 00:25:49,547 This actually releases energy. 446 00:25:49,549 --> 00:25:51,715 As the star cools, it winds up releasing 447 00:25:51,717 --> 00:25:54,251 a little bit more energy than it otherwise would. 448 00:25:54,253 --> 00:25:59,823 Narrator: This unusual heat source could warm up a nearby frozen planet, 449 00:25:59,825 --> 00:26:03,294 giving life a second chance. 450 00:26:03,296 --> 00:26:07,064 Thaller: There will be some extra energy available from these objects. 451 00:26:07,066 --> 00:26:08,766 So this is the time that we have 452 00:26:08,768 --> 00:26:10,834 to cuddle up close to the zombies. 453 00:26:12,338 --> 00:26:16,807 Narrator: Crystallization can rejuvenate old white dwarfs, 454 00:26:16,809 --> 00:26:19,043 and the process could even provide 455 00:26:19,045 --> 00:26:22,713 a spectacular setting for an orbiting planet. 456 00:26:22,715 --> 00:26:24,715 We have a special name 457 00:26:24,717 --> 00:26:27,518 for cooled-down crystallized carbon and oxygen. 458 00:26:27,520 --> 00:26:29,420 We call them diamonds. 459 00:26:29,422 --> 00:26:32,089 The long-term fate of our universe 460 00:26:32,091 --> 00:26:35,960 will be sprinkled with all these glittering diamonds. 461 00:26:37,930 --> 00:26:41,398 A zombie that comes to life and shines like a diamond 462 00:26:41,400 --> 00:26:43,233 might be pretty to look at, 463 00:26:43,235 --> 00:26:47,338 but it's still no guarantee that life could survive here. 464 00:26:48,841 --> 00:26:51,842 You can kind of think of these white dwarfs 465 00:26:51,844 --> 00:26:55,479 as maybe making a little more energy for the universe, 466 00:26:55,481 --> 00:26:58,082 but even that's going to eventually run out. 467 00:26:58,084 --> 00:27:01,885 The whole thing becomes a gigantic crystal and, again, 468 00:27:01,887 --> 00:27:04,755 it's just going to start cooling and fading away. 469 00:27:05,891 --> 00:27:09,159 Narrator: The zombie fizzles out into a dark cinder, 470 00:27:09,161 --> 00:27:12,963 giving off almost no light at all, 471 00:27:12,965 --> 00:27:17,401 but there's another monster lurking in the cosmos. 472 00:27:20,673 --> 00:27:23,807 Thaller: When a star that's much more massive than the sun dies, 473 00:27:23,809 --> 00:27:25,009 it explodes violently, 474 00:27:25,011 --> 00:27:27,745 and during that explosion, the core collapses 475 00:27:27,747 --> 00:27:31,015 and becomes an incredibly dense, small object, 476 00:27:31,017 --> 00:27:35,419 one of the most wonderful real monsters in the universe. 477 00:27:37,123 --> 00:27:39,456 This is a pulsar... 478 00:27:39,458 --> 00:27:44,261 Psr b0329 54, 479 00:27:44,263 --> 00:27:47,364 3,000 light-years away from us. 480 00:27:47,366 --> 00:27:50,034 The pulsar has the mass of the sun, 481 00:27:50,036 --> 00:27:52,436 but is just 12 miles across. 482 00:27:52,438 --> 00:27:57,374 Its rapid spin generates beams of radiation from its poles, 483 00:27:57,376 --> 00:28:00,477 bringing the zombie to life. 484 00:28:01,714 --> 00:28:07,851 Now, we've discovered an alien world orbiting this zombie star. 485 00:28:07,853 --> 00:28:10,587 Mingarelli: In 2017, a new planet 486 00:28:10,589 --> 00:28:12,890 was discovered around a pulsar. 487 00:28:12,892 --> 00:28:15,926 They're about twice the mass of the earth, 488 00:28:15,928 --> 00:28:18,429 and that's really incredible. 489 00:28:18,431 --> 00:28:21,699 Narrator: The pulsar planet sounds intriguing, 490 00:28:21,701 --> 00:28:25,002 but the prospects for life aren't good. 491 00:28:25,004 --> 00:28:29,807 Orbiting a pulsar would be a brutal environment for life. 492 00:28:29,809 --> 00:28:32,743 Mingarelli: It's highly unlikely that there's life 493 00:28:32,745 --> 00:28:35,946 because the radiation from this system would be overwhelming 494 00:28:35,948 --> 00:28:39,116 and likely blow away the atmosphere. 495 00:28:40,186 --> 00:28:42,820 Narrator: As for sustaining life in the universe, 496 00:28:42,822 --> 00:28:47,157 none of these options is what you'd call a safe bet. 497 00:28:47,159 --> 00:28:49,226 ♪ 498 00:28:49,228 --> 00:28:52,796 these are momentary reprieves from the inevitable. 499 00:28:52,798 --> 00:28:55,032 No matter what you do, eventually, 500 00:28:55,034 --> 00:28:57,601 you're going to run out of these gimmes. 501 00:28:57,603 --> 00:29:00,404 You're going to run out of the get-of-jail-free cards. 502 00:29:00,406 --> 00:29:04,508 Inevitably, everything is going to cool and fade away. 503 00:29:04,510 --> 00:29:07,244 ♪ 504 00:29:07,246 --> 00:29:09,913 narrator: This might be game over for stars 505 00:29:09,915 --> 00:29:12,850 and even for life. 506 00:29:12,852 --> 00:29:17,621 But there is still a glimmer of hope hidden in the cosmos, 507 00:29:17,623 --> 00:29:20,791 a star that isn't dying. 508 00:29:20,793 --> 00:29:24,595 It appears blessed with eternal life, 509 00:29:24,597 --> 00:29:27,197 and its color is red. 510 00:29:27,199 --> 00:29:31,034 Red dwarfs -- we are literally surrounded by them, 511 00:29:31,036 --> 00:29:33,237 but they are largely invisible to us. 512 00:29:44,316 --> 00:29:46,683 ♪ 513 00:29:46,685 --> 00:29:49,787 narrator: Illuminating every corner of our night sky 514 00:29:49,789 --> 00:29:52,956 is the light of stars... 515 00:29:52,958 --> 00:29:58,061 But what we see with a naked eye doesn't tell the whole story. 516 00:29:58,063 --> 00:30:00,197 ♪ 517 00:30:00,199 --> 00:30:03,367 thaller: The stars that you're seeing are mainly stars like the sun 518 00:30:03,369 --> 00:30:05,736 or even more massive and even hotter than the sun. 519 00:30:05,738 --> 00:30:08,639 They're bright. You can see them from a distance, 520 00:30:08,641 --> 00:30:11,308 but amazingly, the most common form of star, 521 00:30:11,310 --> 00:30:14,344 by far, are the red dwarf stars. 522 00:30:14,346 --> 00:30:16,513 They're up there right now in the sky, 523 00:30:16,515 --> 00:30:19,616 but they're just too small and too faint to see. 524 00:30:19,618 --> 00:30:23,387 Narrator: Red dwarfs are up to 10 times smaller than the sun, 525 00:30:23,389 --> 00:30:26,123 and they burn less brightly. 526 00:30:26,125 --> 00:30:29,092 Right now, hidden in the night sky, 527 00:30:29,094 --> 00:30:33,564 over three-quarters of the stars in our galaxy are red dwarfs... 528 00:30:33,566 --> 00:30:38,335 And while the larger stars are dying out, 529 00:30:38,337 --> 00:30:41,338 we've never seen a red dwarf die, 530 00:30:41,340 --> 00:30:44,141 making them the best bet for life 531 00:30:44,143 --> 00:30:47,211 to survive the star apocalypse. 532 00:30:47,213 --> 00:30:51,315 When the most massive stars eventually go out 533 00:30:51,317 --> 00:30:54,151 and are not replaced, what will be left 534 00:30:54,153 --> 00:30:58,422 are much, much dimmer stars like red dwarf stars. 535 00:30:58,424 --> 00:31:01,925 Narrator: We've seen star death across the universe, 536 00:31:01,927 --> 00:31:04,294 so why not red dwarfs? 537 00:31:04,296 --> 00:31:06,697 Turns out their size 538 00:31:06,699 --> 00:31:10,400 gives them a crucial advantage over larger stars. 539 00:31:10,402 --> 00:31:13,270 Thaller: The more massive a star is, the hotter it burns. 540 00:31:13,272 --> 00:31:15,672 A red dwarf star burns at a lower temperature. 541 00:31:15,674 --> 00:31:17,574 So it doesn't burn through it's fuel 542 00:31:17,576 --> 00:31:19,710 quite as quickly as a mid-mass star does. 543 00:31:19,712 --> 00:31:22,713 These are like the economy cars of the universe. 544 00:31:22,715 --> 00:31:25,449 They're just sipping on their nuclear fuel, 545 00:31:25,451 --> 00:31:28,185 and they can coast along. 546 00:31:28,187 --> 00:31:31,355 Narrator: Not only that, despite being smaller, 547 00:31:31,357 --> 00:31:34,057 they have access to more fuel. 548 00:31:35,327 --> 00:31:38,595 Our mid-size sun is split into three layers -- 549 00:31:38,597 --> 00:31:41,331 a core, a radiation zone, 550 00:31:41,333 --> 00:31:43,500 and a convective layer. 551 00:31:43,502 --> 00:31:47,304 The radiation zone prevents hydrogen in the top layer 552 00:31:47,306 --> 00:31:50,707 from ever becoming available for the core to burn. 553 00:31:50,709 --> 00:31:52,976 So the sun can only access 554 00:31:52,978 --> 00:31:57,114 about 10 percent of its total hydrogen fuel. 555 00:31:57,116 --> 00:32:01,251 Once the hydrogen in our sun's core runs out, 556 00:32:01,253 --> 00:32:04,254 its days are numbered. 557 00:32:04,256 --> 00:32:06,490 In some ways, these mid-sized stars 558 00:32:06,492 --> 00:32:08,158 end up starving themselves. 559 00:32:08,160 --> 00:32:11,561 Narrator: The smaller red dwarfs are different. 560 00:32:11,563 --> 00:32:15,065 They can access all the hydrogen they want. 561 00:32:15,067 --> 00:32:18,568 Plait: In low-mass stars, outside of the core, 562 00:32:18,570 --> 00:32:21,505 this outer layer is fully convective. 563 00:32:21,507 --> 00:32:25,375 What that means is, stuff near the core rises to the surface 564 00:32:25,377 --> 00:32:28,312 and then drops back down all the way to the core, 565 00:32:28,314 --> 00:32:30,514 and that means if you have hydrogen somewhere 566 00:32:30,516 --> 00:32:33,150 outside of the core, eventually, it's going to make 567 00:32:33,152 --> 00:32:35,619 its way down there, and it can be used for fuel. 568 00:32:35,621 --> 00:32:37,854 Hopkins: The red dwarf has access to everything 569 00:32:37,856 --> 00:32:39,189 at the all-you-can-eat buffet. 570 00:32:39,191 --> 00:32:41,758 It can grab stuff from the distant regions 571 00:32:41,760 --> 00:32:44,795 at the surface of the star and bring it all the way 572 00:32:44,797 --> 00:32:48,098 down the gullet to the heart of the star. 573 00:32:49,201 --> 00:32:52,436 Narrator: This all-you-can-eat hydrogen buffet 574 00:32:52,438 --> 00:32:56,540 extends the life span of red dwarfs to incredible lengths. 575 00:32:56,542 --> 00:33:00,344 The universe is over 13 billion years old, 576 00:33:00,346 --> 00:33:04,114 but any red dwarf that age is a toddler. 577 00:33:05,517 --> 00:33:07,384 A red dwarf, even if it was born 578 00:33:07,386 --> 00:33:09,319 at the very beginning of the universe 579 00:33:09,321 --> 00:33:11,054 when red dwarfs could first form, 580 00:33:11,056 --> 00:33:14,725 even today, it's just a tiny fraction of its lifespan. 581 00:33:14,727 --> 00:33:17,294 They can last for trillions of years, 582 00:33:17,296 --> 00:33:20,564 thousands of times the current age of the universe. 583 00:33:20,566 --> 00:33:22,632 Sutter: Thirteen billion years old -- 584 00:33:22,634 --> 00:33:24,801 that seems like a long time, 585 00:33:24,803 --> 00:33:26,603 but a small red dwarf, 586 00:33:26,605 --> 00:33:28,805 it's barely out of diapers. 587 00:33:28,807 --> 00:33:30,607 ♪ 588 00:33:30,609 --> 00:33:33,043 narrator: Red dwarf stars will not die out 589 00:33:33,045 --> 00:33:36,580 for 10 trillion years or more... 590 00:33:36,582 --> 00:33:40,484 And we're discovering they have another trump card 591 00:33:40,486 --> 00:33:42,252 that's good news for life. 592 00:33:42,254 --> 00:33:46,423 ♪ 593 00:33:46,425 --> 00:33:48,759 February 2017. 594 00:33:48,761 --> 00:33:51,495 Nasa announced the discovery of a system 595 00:33:51,497 --> 00:33:55,165 in the aquarius constellation called trappist-1 596 00:33:55,167 --> 00:34:00,570 where seven earth-sized planets orbit a red dwarf star. 597 00:34:01,707 --> 00:34:04,975 Plait: It turns out that red dwarfs, apparently, 598 00:34:04,977 --> 00:34:07,444 are really good at making planets, 599 00:34:07,446 --> 00:34:10,747 including planets that are roughly the size of the earth. 600 00:34:10,749 --> 00:34:16,186 That's really cool because these stars last a long time. 601 00:34:16,188 --> 00:34:18,688 If they have planets orbiting them with life, 602 00:34:18,690 --> 00:34:22,692 they could outlast our solar system by trillions of years. 603 00:34:23,762 --> 00:34:28,465 Narrator: Sounds promising, but red dwarfs have an ugly side. 604 00:34:30,235 --> 00:34:32,569 In October 2018, 605 00:34:32,571 --> 00:34:35,305 astronomers turned the hubble space telescope 606 00:34:35,307 --> 00:34:38,608 to a series of young red dwarf stars 607 00:34:38,610 --> 00:34:41,845 in the tucana-horologium association. 608 00:34:41,847 --> 00:34:47,851 They witnessed these infants throwing daily stellar tantrums. 609 00:34:47,853 --> 00:34:49,920 Thaller: Even though they're the smallest stars, 610 00:34:49,922 --> 00:34:52,389 they actually have some of the strongest flares 611 00:34:52,391 --> 00:34:54,357 and storms on them. 612 00:34:54,359 --> 00:34:56,893 Narrator: Red dwarfs can emit flares 613 00:34:56,895 --> 00:35:00,597 10,000 times more powerful than the sun. 614 00:35:00,599 --> 00:35:04,634 These flares would cook any nearby planets. 615 00:35:05,637 --> 00:35:07,370 Oluseyi: When a red dwarf star forms, 616 00:35:07,372 --> 00:35:09,005 they're rotating very rapidly, 617 00:35:09,007 --> 00:35:11,408 and this creates a lot of magnetic activity 618 00:35:11,410 --> 00:35:14,578 which creates flares and mass ejections. 619 00:35:14,580 --> 00:35:16,947 Narrator: For life to exist, 620 00:35:16,949 --> 00:35:21,251 it would have to wait for infant red dwarfs to grow up. 621 00:35:22,754 --> 00:35:24,821 Oluseyi: As a red dwarf gets older, 622 00:35:24,823 --> 00:35:27,457 there's drag between the magnetic fields 623 00:35:27,459 --> 00:35:30,127 in space as it rotates, and that has the effect 624 00:35:30,129 --> 00:35:32,129 of slowing down its rate of rotation. 625 00:35:32,131 --> 00:35:34,431 And so this means the activity settles down. 626 00:35:34,433 --> 00:35:38,034 So maybe later, in this life of a red dwarf star, 627 00:35:38,036 --> 00:35:40,570 they can support planets with life. 628 00:35:42,908 --> 00:35:47,177 Narrator: Red dwarf stars will dominate the future universe 629 00:35:47,179 --> 00:35:50,914 and may give life a chance to survive. 630 00:35:50,916 --> 00:35:55,118 These small red stars are extremely long-lived, 631 00:35:55,120 --> 00:35:57,754 but no star is immortal. 632 00:35:57,756 --> 00:36:01,324 Even though they're really going through their nuclear fuel 633 00:36:01,326 --> 00:36:06,329 very slowly, there's just not enough fuel to last forever. 634 00:36:07,599 --> 00:36:10,800 Narrator: These little stars will die out eventually. 635 00:36:10,802 --> 00:36:16,106 Unlike their larger stellar siblings, they'll go quietly. 636 00:36:16,108 --> 00:36:18,241 Well, it actually just gets hotter, 637 00:36:18,243 --> 00:36:21,178 and the color of a star depends on its temperature. 638 00:36:21,180 --> 00:36:24,214 So as the red dwarf gets hotter, it turns bluer. 639 00:36:24,216 --> 00:36:27,150 So sometime in the very distant future, 640 00:36:27,152 --> 00:36:28,485 some of these red dwarfs 641 00:36:28,487 --> 00:36:31,254 are actually going to become blue dwarfs. 642 00:36:31,256 --> 00:36:35,725 Narrator: The universe isn't old enough for blue dwarfs to exist yet. 643 00:36:35,727 --> 00:36:38,228 But trillions of years from now, 644 00:36:38,230 --> 00:36:43,133 a dim blue glow will complete the star apocalypse. 645 00:36:44,236 --> 00:36:48,205 There will be a last star, one last red dwarf, 646 00:36:48,207 --> 00:36:51,608 maybe now turning blue as it warms up, 647 00:36:51,610 --> 00:36:55,712 but it too will eventually cool off, fade away. 648 00:36:56,848 --> 00:36:59,416 And there will be no more stars in the universe. 649 00:36:59,418 --> 00:37:01,418 It is inevitable. 650 00:37:01,420 --> 00:37:03,453 ♪ 651 00:37:03,455 --> 00:37:06,556 narrator: In this dark, starless universe, 652 00:37:06,558 --> 00:37:09,826 prospects for life seem impossible. 653 00:37:09,828 --> 00:37:14,064 But will something else take the place of stars? 654 00:37:14,066 --> 00:37:16,700 Oluseyi: As we get to the end of the universe, 655 00:37:16,702 --> 00:37:19,869 things get really cold, but they also get really weird. 656 00:37:35,854 --> 00:37:39,155 Narrator: Trillions of years from now, the star apocalypse 657 00:37:39,157 --> 00:37:42,692 will leave the universe empty and dark, 658 00:37:42,694 --> 00:37:45,295 a never-ending night. 659 00:37:46,331 --> 00:37:47,964 The universe at this time 660 00:37:47,966 --> 00:37:49,866 is nothing like the universe of today. 661 00:37:49,868 --> 00:37:55,372 There's no light, and it's really cold and very lonely. 662 00:37:55,374 --> 00:37:59,209 When all of the stars die and the light goes away, 663 00:37:59,211 --> 00:38:01,211 anything that relies on the heat 664 00:38:01,213 --> 00:38:04,414 and the processes from these stars will start to die. 665 00:38:04,416 --> 00:38:06,283 ♪ 666 00:38:06,285 --> 00:38:08,585 sutter: Once all the lights go out, 667 00:38:08,587 --> 00:38:12,389 the only things that will remain will be the leftovers. 668 00:38:12,391 --> 00:38:15,191 Narrator: With stars as we know them long gone, 669 00:38:15,193 --> 00:38:17,961 could something else spark into existence 670 00:38:17,963 --> 00:38:20,363 in this cosmic wasteland? 671 00:38:20,365 --> 00:38:23,300 You'd think that's it, no more star formation. 672 00:38:23,302 --> 00:38:27,203 But the universe still has a few tricks up its sleeve. 673 00:38:27,205 --> 00:38:29,873 Narrator: Over the history of the universe, 674 00:38:29,875 --> 00:38:32,642 generations of stars have lived and died. 675 00:38:32,644 --> 00:38:36,112 They released heavy metal elements into the universe, 676 00:38:36,114 --> 00:38:39,749 building materials for a new kind of star, 677 00:38:39,751 --> 00:38:42,285 and stars born from these new materials 678 00:38:42,287 --> 00:38:46,823 can do things their ancestors could not. 679 00:38:46,825 --> 00:38:50,894 As you enrich the universe, as more and more metals 680 00:38:50,896 --> 00:38:52,629 get produced over time, 681 00:38:52,631 --> 00:38:56,333 you can lower the temperature needed 682 00:38:56,335 --> 00:38:58,935 for fusion reactions in a star. 683 00:38:58,937 --> 00:39:02,639 Narrator: With lower temperatures needed for fusion, 684 00:39:02,641 --> 00:39:06,376 stars have become smaller and smaller. 685 00:39:06,378 --> 00:39:08,978 O'dowd: Currently, the smallest possible star 686 00:39:08,980 --> 00:39:11,648 is a little under 10 percent the sun's mass. 687 00:39:11,650 --> 00:39:14,084 But eventually it may be possible to form stars 688 00:39:14,086 --> 00:39:16,686 that have around 4 percent the sun's mass. 689 00:39:18,256 --> 00:39:21,725 Narrator: Hundreds of trillions of years in the future, 690 00:39:21,727 --> 00:39:24,461 a new star may dominate the universe, 691 00:39:24,463 --> 00:39:30,567 built from scraps left over from generations of dead stars, 692 00:39:30,569 --> 00:39:32,669 a star so small 693 00:39:32,671 --> 00:39:36,039 that it burns cold instead of hot. 694 00:39:37,476 --> 00:39:39,342 One of the weirdest types of stars 695 00:39:39,344 --> 00:39:42,178 that scientists hypothesize might exist in the far future 696 00:39:42,180 --> 00:39:43,880 is the frozen star. 697 00:39:45,417 --> 00:39:49,586 Sutter: You can start forming stars that are very, very small 698 00:39:49,588 --> 00:39:52,922 and very cold, where nuclear fusion 699 00:39:52,924 --> 00:39:57,494 is happening in the core, but the surfaces are cold. 700 00:39:57,496 --> 00:40:00,830 ♪ 701 00:40:00,832 --> 00:40:02,866 narrator: These small, cold objects 702 00:40:02,868 --> 00:40:04,968 will be thousands of times dimmer 703 00:40:04,970 --> 00:40:08,471 than the faintest star we see today. 704 00:40:08,473 --> 00:40:11,875 So cold, the temperatures on the surface 705 00:40:11,877 --> 00:40:15,478 could reach just 32 degrees fahrenheit... 706 00:40:15,480 --> 00:40:19,783 And ice clouds may form in the star's atmosphere. 707 00:40:19,785 --> 00:40:23,420 They are so much cooler than stars now. 708 00:40:23,422 --> 00:40:27,924 They could actually have ice, water ice, on their surface, 709 00:40:27,926 --> 00:40:31,494 even though they are technically stars. 710 00:40:31,496 --> 00:40:36,099 Sutter: It's literal water-ice covering the surface of a star, 711 00:40:36,101 --> 00:40:39,602 the same ice that you can use for ice-skating 712 00:40:39,604 --> 00:40:41,571 or ice racing or curling. 713 00:40:41,573 --> 00:40:43,306 You could do all of this 714 00:40:43,308 --> 00:40:46,476 on the surface of a star in the far future. 715 00:40:47,646 --> 00:40:50,046 Narrator: It's hard to predict if life could arise 716 00:40:50,048 --> 00:40:53,316 on planets orbiting frozen stars. 717 00:40:55,454 --> 00:40:59,689 We won't know until one appears... 718 00:40:59,691 --> 00:41:03,827 And that won't be for a very long time. 719 00:41:05,497 --> 00:41:07,330 The universe is far too young 720 00:41:07,332 --> 00:41:09,632 for even the first one of these things 721 00:41:09,634 --> 00:41:11,468 to even be a glimmer of an idea. 722 00:41:11,470 --> 00:41:14,103 So if you want to wait, you know, a quadrillion years, 723 00:41:14,105 --> 00:41:15,939 then we can find out. 724 00:41:15,941 --> 00:41:18,775 Narrator: Stars helped create us, 725 00:41:18,777 --> 00:41:21,077 building and spreading the ingredients 726 00:41:21,079 --> 00:41:23,146 for life to develop, 727 00:41:23,148 --> 00:41:25,181 but the coming star apocalypse 728 00:41:25,183 --> 00:41:27,851 may mean the end of life, 729 00:41:27,853 --> 00:41:30,186 just not for a while. 730 00:41:31,656 --> 00:41:36,359 Small red stars will continue to illuminate the darkness... 731 00:41:36,361 --> 00:41:41,064 Safe havens for life to survive and even flourish. 732 00:41:41,066 --> 00:41:42,799 As for us on earth, 733 00:41:42,801 --> 00:41:46,236 we should be most thankful for one star 734 00:41:46,238 --> 00:41:50,473 because without it, we simply wouldn't exist. 735 00:41:50,475 --> 00:41:53,643 Thaller: I really want you to never experience a sunny day again 736 00:41:53,645 --> 00:41:55,011 and not think about this. 737 00:41:55,013 --> 00:41:57,380 The sun, someday, will burn out, 738 00:41:57,382 --> 00:41:59,549 and so will all of the other stars. 739 00:41:59,551 --> 00:42:03,620 We are in this wonderful era of light and warmth 740 00:42:03,622 --> 00:42:05,154 coming out of the sky, 741 00:42:05,156 --> 00:42:09,058 and everything is going to go dark, absolutely everything, 742 00:42:09,060 --> 00:42:11,160 everywhere in the universe. 743 00:42:11,162 --> 00:42:14,430 So for the time being, you know, enjoy the light. 744 00:42:14,432 --> 00:42:16,533 Step outside, enjoy the sun, 745 00:42:16,535 --> 00:42:19,669 and think about how lucky we are to live in this time. 746 00:42:19,671 --> 00:42:23,473 ♪ 747 00:42:23,475 --> 00:42:27,844 ♪