1 00:00:01,301 --> 00:00:03,268 ROWE: White dwarfs, 2 00:00:03,370 --> 00:00:06,171 small stars that pack a big punch. 3 00:00:06,272 --> 00:00:09,508 When white dwarfs were first discovered, 4 00:00:09,609 --> 00:00:13,012 astronomers' reaction was no, no, no, no, 5 00:00:13,113 --> 00:00:15,280 no, no, no, that can't be real. 6 00:00:15,382 --> 00:00:17,149 BULLOCK: What's going on inside these things 7 00:00:17,250 --> 00:00:19,885 can only be described as seriously weird. 8 00:00:19,986 --> 00:00:21,754 ROWE: They're the cooling corpses of stars 9 00:00:21,855 --> 00:00:23,389 like our sun, 10 00:00:23,490 --> 00:00:25,958 but new research proves white dwarfs are 11 00:00:26,059 --> 00:00:28,160 one of the driving forces of our universe. 12 00:00:29,295 --> 00:00:32,998 PLAIT: They eat planets, they flare out in high-energy light. 13 00:00:33,066 --> 00:00:35,567 They can really explode. 14 00:00:35,668 --> 00:00:37,136 And they can tell us literally 15 00:00:37,237 --> 00:00:40,372 about the nature of the universe itself. 16 00:00:40,473 --> 00:00:41,573 NARRATOR: And there's a dirty secret at 17 00:00:41,674 --> 00:00:43,876 the heart of white dwarf science. 18 00:00:43,977 --> 00:00:45,778 HOPKINS: We see dead stars exploding, 19 00:00:45,879 --> 00:00:47,946 and we still don't understand why they're doing it. 20 00:00:48,048 --> 00:00:50,783 ROWE: Have scientists finally discovered how these small 21 00:00:50,884 --> 00:00:54,720 stars could be such massive galactic players? 22 00:00:57,424 --> 00:00:59,491 [explosion blasts] 23 00:01:03,229 --> 00:01:05,798 December 2018. 24 00:01:05,899 --> 00:01:09,368 Astronomers spot strange flares coming from 25 00:01:09,469 --> 00:01:13,872 a galaxy 250 million light-years from Earth, 26 00:01:13,973 --> 00:01:16,008 GSN 069. 27 00:01:17,477 --> 00:01:20,946 We know that GSN 069 has a supermassive black hole in 28 00:01:21,047 --> 00:01:22,281 its center, equal to about 29 00:01:22,382 --> 00:01:24,983 half a million times the mass of the sun. 30 00:01:25,085 --> 00:01:27,086 That's a big black hole, 31 00:01:27,187 --> 00:01:29,521 and it blasts out X-rays in 32 00:01:29,622 --> 00:01:33,325 a very, very steady pace, 33 00:01:33,426 --> 00:01:36,995 every nine hours. Why? 34 00:01:38,698 --> 00:01:40,866 ROWE: The flares are so energetic and regular, 35 00:01:40,967 --> 00:01:44,036 the supermassive black hole must be eating the mass of 36 00:01:44,137 --> 00:01:46,572 the planet Mercury three times a day. 37 00:01:48,241 --> 00:01:50,309 The big question is what's feeding this black hole 38 00:01:50,410 --> 00:01:51,376 such a huge dinner? 39 00:01:52,812 --> 00:01:56,014 ROWE: In March 2020, scientists found the answer. 40 00:01:58,451 --> 00:02:00,786 An unlucky star at the end of its life 41 00:02:00,887 --> 00:02:05,124 had wandered into the death zone of the black hole. 42 00:02:05,225 --> 00:02:07,593 OLUSEYI: A star getting too close to a supermassive 43 00:02:07,694 --> 00:02:09,761 black hole is like a glazed doughnut 44 00:02:09,863 --> 00:02:11,063 getting too close to me. 45 00:02:11,164 --> 00:02:13,966 That thing just is not gonna make it. 46 00:02:14,067 --> 00:02:16,869 HOPKINS: Stars to get too close to a black hole 47 00:02:16,970 --> 00:02:18,370 get torn apart. 48 00:02:18,471 --> 00:02:20,873 They sort of get attacked by the black hole, 49 00:02:20,974 --> 00:02:22,941 and some of that material is also getting launched 50 00:02:23,042 --> 00:02:25,744 off in very powerful winds and jets and streams 51 00:02:25,845 --> 00:02:27,513 getting out. 52 00:02:29,282 --> 00:02:31,316 ROWE: Somehow, the star survives its close 53 00:02:31,417 --> 00:02:34,153 encounter with the supermassive black hole. 54 00:02:34,254 --> 00:02:39,224 Further investigation reveals it's a small, compact star, 55 00:02:39,325 --> 00:02:40,492 a white dwarf. 56 00:02:41,794 --> 00:02:45,998 So what makes this tiny star almost indestructible? 57 00:02:46,099 --> 00:02:48,567 The answer lies in how it's formed. 58 00:02:48,668 --> 00:02:51,570 We get a clue if we look at the life cycle of a star. 59 00:02:51,671 --> 00:02:55,574 It's burning hydrogen into helium, that's causing nuclear 60 00:02:55,675 --> 00:02:59,344 fusion, and that causes a star to stay stable. 61 00:02:59,445 --> 00:03:03,048 There's this delicate balance between radiation pressure 62 00:03:03,149 --> 00:03:06,818 from that nuclear fusion pushing out and gravitational pressure 63 00:03:06,920 --> 00:03:08,620 pulling in. 64 00:03:08,721 --> 00:03:11,790 But when stars like our sun near the end of their life, 65 00:03:11,891 --> 00:03:14,493 they run out of hydrogen fuel. 66 00:03:14,594 --> 00:03:17,262 ROWE: The sun-like star makes more and more helium, 67 00:03:17,363 --> 00:03:19,131 which builds up in its center. 68 00:03:20,233 --> 00:03:21,900 Gradually, the immense weight of 69 00:03:22,001 --> 00:03:25,304 the star's outer layers crushes the helium core. 70 00:03:27,473 --> 00:03:30,509 OLUSEYI: As the core ages, it gets smaller and hotter, 71 00:03:30,610 --> 00:03:33,212 which increases the rate of nuclear reactions. 72 00:03:34,681 --> 00:03:37,583 ROWE: These nuclear fusion reactions produce more energy, 73 00:03:37,684 --> 00:03:40,886 which pushes the outer layer, or envelope, outwards. 74 00:03:42,488 --> 00:03:45,591 Because there's more energy flowing through the envelope, 75 00:03:45,692 --> 00:03:48,193 the envelope swells up. 76 00:03:48,294 --> 00:03:52,998 ROWE: The star expands to around 100 times its original size. 77 00:03:53,099 --> 00:03:56,935 The yellow star becomes a red giant. 78 00:03:57,036 --> 00:04:00,739 Eventually, red giants shed their outer layers, 79 00:04:00,840 --> 00:04:05,410 forming stunning gas shells called planetary nebulas. 80 00:04:08,715 --> 00:04:12,484 Planetary nebulae are the most beautiful objects in space. 81 00:04:12,585 --> 00:04:14,019 They're all spectacular. 82 00:04:14,120 --> 00:04:18,223 A star that ends its life in one of these planetary nebulas 83 00:04:18,324 --> 00:04:20,559 leaves behind a white dwarf at the center, 84 00:04:20,660 --> 00:04:23,528 and this white dwarf is essentially a cinder, 85 00:04:23,630 --> 00:04:25,130 a stellar cinder. 86 00:04:25,231 --> 00:04:28,267 It's what's left after nuclear fusion 87 00:04:28,368 --> 00:04:31,470 is no longer possible for that particular star. 88 00:04:31,571 --> 00:04:34,940 ROWE: All that remains, a glowing white dwarf, 89 00:04:35,041 --> 00:04:37,309 the leftover core of the dead star. 90 00:04:38,678 --> 00:04:41,513 But in galaxy GSN 069, 91 00:04:41,614 --> 00:04:45,517 the supermassive black hole turbocharged the process. 92 00:04:45,618 --> 00:04:49,021 It stripped off the outer layers of the red giant 93 00:04:49,122 --> 00:04:50,889 in a matter of days. 94 00:04:50,990 --> 00:04:52,424 HOPKINS: The black hole has almost eaten 95 00:04:52,525 --> 00:04:54,826 all the juicy parts, all the easy-to-get-at parts 96 00:04:54,927 --> 00:04:57,195 of star, leaving behind the sort of 97 00:04:57,297 --> 00:05:00,899 bone or the leftovers of the white dwarf. 98 00:05:01,000 --> 00:05:03,035 ROWE: This white dwarf is just 1/5 99 00:05:03,136 --> 00:05:06,071 of the mass of the sun. 100 00:05:06,172 --> 00:05:08,573 How can such a small star survive 101 00:05:08,675 --> 00:05:11,109 being so close to a black hole? 102 00:05:11,210 --> 00:05:14,613 PLAIT: You might think that because a white dwarf is small, 103 00:05:14,714 --> 00:05:15,814 it's not gonna last very long, 104 00:05:15,915 --> 00:05:18,083 because there's not that much stuff there to eat, 105 00:05:18,184 --> 00:05:21,086 but it turns out it's quite the opposite. 106 00:05:21,187 --> 00:05:24,589 ROWE: The pocket-sized white dwarf is packed full of matter. 107 00:05:25,825 --> 00:05:28,360 If it were a normal star, it would have been shredded 108 00:05:28,461 --> 00:05:31,563 long ago, but because it's such a dense, 109 00:05:31,664 --> 00:05:34,700 tight ball of matter, it survives. 110 00:05:34,801 --> 00:05:37,903 Imagine taking the sun and crushing it down 111 00:05:38,004 --> 00:05:40,105 to just about the size of the Earth. 112 00:05:40,206 --> 00:05:42,908 Same mass, but now packed way 113 00:05:43,009 --> 00:05:46,278 more tightly, so a basketball-worth of this 114 00:05:46,379 --> 00:05:50,782 stuff would weigh as much as 35 blue whales. 115 00:05:50,883 --> 00:05:54,586 ROWE: The white dwarf's extreme density protects it from 116 00:05:54,687 --> 00:05:58,190 the gravitational onslaught of the supermassive black hole. 117 00:05:59,492 --> 00:06:03,628 Its orbit takes it near that black hole every nine hours, 118 00:06:03,730 --> 00:06:07,032 and every time it encounters the black hole, some of its 119 00:06:07,133 --> 00:06:09,134 material gets sipped off. 120 00:06:09,235 --> 00:06:10,702 They're playing a game of interstellar 121 00:06:10,803 --> 00:06:12,704 tug of war with one another. 122 00:06:12,805 --> 00:06:14,840 The black hole is bigger, so it's going to win. 123 00:06:14,941 --> 00:06:17,909 But the white dwarf is very dense, so it's very tough, 124 00:06:18,010 --> 00:06:21,113 and it's able to hang in there for quite a long time. 125 00:06:21,214 --> 00:06:22,414 OLUSEYI: It's gonna stay in orbit around 126 00:06:22,515 --> 00:06:25,650 a supermassive black hole for billions of years. 127 00:06:25,752 --> 00:06:28,820 Talk about David and Goliath. 128 00:06:28,921 --> 00:06:31,490 ROWE: When astronomers first discovered white dwarfs, 129 00:06:31,591 --> 00:06:33,024 they thought they shouldn't exist. 130 00:06:34,327 --> 00:06:37,162 How could something have such an extreme density 131 00:06:37,230 --> 00:06:39,197 and not collapse under its own weight? 132 00:06:41,000 --> 00:06:43,535 Quantum mechanics, the science of atomic 133 00:06:43,636 --> 00:06:46,571 and subatomic particles has the answer. 134 00:06:46,672 --> 00:06:50,041 SUTTER: We're used to the rules of physics up here 135 00:06:50,143 --> 00:06:51,576 in the macroscopic world, 136 00:06:51,677 --> 00:06:54,546 but when you zoom down into the subatomic world, 137 00:06:54,647 --> 00:06:57,282 things get weird. 138 00:06:57,383 --> 00:07:00,886 Here we have the electron, one of the tiniest 139 00:07:00,987 --> 00:07:02,587 particles in the universe, 140 00:07:02,688 --> 00:07:05,891 and it's these little electrons that are doing 141 00:07:05,992 --> 00:07:09,761 the work of supporting an entire star. 142 00:07:09,862 --> 00:07:12,697 Electrons really don't like being squashed 143 00:07:12,799 --> 00:07:14,032 into a small space. 144 00:07:14,167 --> 00:07:17,536 If you try to squash too many of them into too small a space, 145 00:07:17,637 --> 00:07:19,070 they'll push back really hard, 146 00:07:19,172 --> 00:07:21,940 and this is an effect called degeneracy pressure. 147 00:07:23,609 --> 00:07:26,244 ROWE: These degenerate electrons stop white dwarfs 148 00:07:26,345 --> 00:07:27,646 from collapsing, 149 00:07:27,747 --> 00:07:31,316 but they give these stars strange qualities. 150 00:07:31,417 --> 00:07:33,485 OLUSEYI: White dwarfs behave 151 00:07:33,586 --> 00:07:35,253 very differently than normal matter. 152 00:07:35,354 --> 00:07:37,189 Take planets and stars. 153 00:07:37,290 --> 00:07:39,991 They become bigger when they gain mass. 154 00:07:40,092 --> 00:07:42,527 White dwarfs are the exact opposite. 155 00:07:42,628 --> 00:07:45,931 As they gain mass, they get smaller. 156 00:07:46,032 --> 00:07:47,365 ROWE: The more massive a white dwarf, 157 00:07:47,467 --> 00:07:49,935 the tighter the electrons squeeze together, 158 00:07:50,036 --> 00:07:53,038 and the smaller and denser the star gets. 159 00:07:55,274 --> 00:07:56,374 The high density means 160 00:07:56,476 --> 00:07:59,544 the white dwarf's structure is also strange. 161 00:07:59,645 --> 00:08:02,047 It has an extremely thin atmosphere, 162 00:08:02,148 --> 00:08:05,951 made of hydrogen or, occasionally, helium gas. 163 00:08:06,052 --> 00:08:08,920 If you were to take an Earth skyscraper and put it on 164 00:08:09,021 --> 00:08:10,155 a white dwarf star, 165 00:08:10,256 --> 00:08:12,390 if you climb to the top of that skyscraper, 166 00:08:12,492 --> 00:08:14,893 you'd be outside of the white dwarf's atmosphere. 167 00:08:14,994 --> 00:08:17,562 You'd actually be in space. 168 00:08:17,663 --> 00:08:20,465 ROWE: Beneath the thin atmosphere lies a surface 169 00:08:20,566 --> 00:08:23,134 of dense helium around 30 miles thick. 170 00:08:25,004 --> 00:08:26,671 It surrounds an interior made 171 00:08:26,772 --> 00:08:29,341 of superheated liquid carbon and oxygen. 172 00:08:31,310 --> 00:08:32,744 A white dwarf at its surface 173 00:08:32,845 --> 00:08:34,145 can be a half a million degrees. 174 00:08:34,247 --> 00:08:36,314 It's even hotter in the interior, 175 00:08:36,415 --> 00:08:38,617 and so that kind of material, 176 00:08:38,718 --> 00:08:42,587 it's not gonna behave the way normal matter does. 177 00:08:42,688 --> 00:08:44,589 ROWE: Eventually, over billions of years, 178 00:08:44,690 --> 00:08:47,959 the center of the white dwarf cools down into a solid. 179 00:08:49,161 --> 00:08:51,496 CHRISTIANSEN: As the carbon and oxygen atoms cool down, 180 00:08:51,597 --> 00:08:52,797 they form a crystal. 181 00:08:52,899 --> 00:08:54,966 Diamonds are actually crystals of carbon, 182 00:08:55,067 --> 00:08:57,202 so at the center of these cool white dwarfs 183 00:08:57,303 --> 00:08:59,070 could be a diamond the size of the Earth. 184 00:08:59,171 --> 00:09:03,542 ROWE: White dwarfs gradually give off their remaining energy 185 00:09:03,643 --> 00:09:06,978 until there's just a cold, dead ball of matter, 186 00:09:07,079 --> 00:09:08,647 a black dwarf. 187 00:09:08,748 --> 00:09:11,016 HOPKINS: We've never seen what we call a black dwarf, 188 00:09:11,117 --> 00:09:12,717 and there's a simple reason for that. 189 00:09:12,818 --> 00:09:14,920 It takes a tremendous amount of time, 190 00:09:15,021 --> 00:09:17,622 many tens of billions of years, longer than the age of 191 00:09:17,723 --> 00:09:19,357 the universe, to reach that point. 192 00:09:21,260 --> 00:09:24,429 ROWE: This is the dark destiny of most midsized stars, 193 00:09:24,530 --> 00:09:26,765 including our sun. 194 00:09:26,866 --> 00:09:31,136 This long, slow death may make white dwarfs seem ordinary, 195 00:09:32,505 --> 00:09:34,406 but these tiny stars could answer 196 00:09:34,507 --> 00:09:37,876 some big questions about our universe. 197 00:09:37,977 --> 00:09:41,112 PONTZEN: They might be small, and they might be dim, 198 00:09:41,213 --> 00:09:44,849 but they are essential for our understanding of physics. 199 00:09:46,319 --> 00:09:48,853 ROWE: New research into white dwarfs may answer 200 00:09:48,955 --> 00:09:50,689 one of the biggest questions of all... 201 00:09:50,790 --> 00:09:54,125 Can life survive the death of its star? 202 00:10:05,871 --> 00:10:07,739 ROWE: In the past, we've underestimated 203 00:10:07,840 --> 00:10:09,407 white dwarfs, 204 00:10:09,508 --> 00:10:13,578 but now they're causing a buzz among astronomers. 205 00:10:13,679 --> 00:10:15,680 One of the big questions over the last 206 00:10:15,781 --> 00:10:20,852 decade is could a planet survive around a white dwarf? 207 00:10:20,953 --> 00:10:22,754 The logical answer would be no. 208 00:10:22,855 --> 00:10:24,456 On their way to becoming white dwarfs, 209 00:10:24,557 --> 00:10:26,825 stars evolve through a red giant phase. 210 00:10:31,097 --> 00:10:33,198 They expand to become very huge. 211 00:10:35,334 --> 00:10:36,568 So we figured any planets around 212 00:10:36,669 --> 00:10:39,070 these stars might just get eaten. 213 00:10:42,775 --> 00:10:46,745 ROWE: In December of 2019, evidence from the constellation 214 00:10:46,846 --> 00:10:49,681 of Cancer turned that idea on its head. 215 00:10:49,782 --> 00:10:54,119 Astronomers spotted a strange-looking white dwarf 216 00:10:54,220 --> 00:10:56,821 about 1,500 light-years from Earth. 217 00:11:00,159 --> 00:11:02,727 Subtle variations in light from the star 218 00:11:02,828 --> 00:11:04,729 revealed a mystery... 219 00:11:04,830 --> 00:11:08,466 The elements oxygen and sulfur in amounts never 220 00:11:08,567 --> 00:11:12,070 before seen on the surface of a white dwarf. 221 00:11:12,171 --> 00:11:14,572 We know what the chemical signature of a white dwarf is, 222 00:11:14,674 --> 00:11:16,107 and this stuck out like a sore thumb. 223 00:11:17,476 --> 00:11:19,511 ROWE: Normally, hydrogen and helium 224 00:11:19,612 --> 00:11:22,113 make up the outer layers of a white dwarf. 225 00:11:22,214 --> 00:11:23,381 Oxygen and sulfur 226 00:11:23,482 --> 00:11:25,050 are heavier than hydrogen and helium, 227 00:11:25,151 --> 00:11:27,152 and they should have sunk down, but we still see them 228 00:11:27,253 --> 00:11:30,689 there, so they must have gotten there recently. 229 00:11:30,790 --> 00:11:33,725 ROWE: Using ESO's Very Large Telescope in Chile, 230 00:11:33,826 --> 00:11:37,395 astronomers took a closer look. 231 00:11:37,496 --> 00:11:40,298 They discovered a small, Earth-sized white dwarf 232 00:11:40,366 --> 00:11:43,601 surrounded by a huge gas disc roughly 10 times 233 00:11:43,703 --> 00:11:45,637 the width of the sun. 234 00:11:45,771 --> 00:11:48,973 The disc contained hydrogen, oxygen, and sulfur. 235 00:11:49,075 --> 00:11:52,444 SHIELDS: A system like this had never been seen before, 236 00:11:52,545 --> 00:11:55,213 and so the next step was to look at a profile of these 237 00:11:55,314 --> 00:11:57,082 elements and figure out where 238 00:11:57,183 --> 00:11:58,950 we'd seen something similar. 239 00:11:59,051 --> 00:12:02,821 And the amazing thing is, we have. 240 00:12:02,922 --> 00:12:06,991 We've seen these elements in the deeper layers of the ice 241 00:12:07,093 --> 00:12:08,860 giants of our solar system, 242 00:12:08,961 --> 00:12:10,528 Uranus and Neptune. 243 00:12:12,431 --> 00:12:14,899 ROWE: Hidden in the gas ring is a giant, 244 00:12:15,000 --> 00:12:17,402 Neptune-like icy planet. 245 00:12:17,503 --> 00:12:19,971 It's twice as large as the star, 246 00:12:20,072 --> 00:12:24,109 but the fierce 50,000-degree heat from the white dwarf is 247 00:12:24,210 --> 00:12:26,578 slowly evaporating this orbiting planet. 248 00:12:26,679 --> 00:12:28,246 SHIELDS: The white dwarf 249 00:12:28,347 --> 00:12:32,050 is bombarding the planet with high-energy radiation, X-rays, 250 00:12:32,151 --> 00:12:33,218 UV rays. 251 00:12:33,319 --> 00:12:36,087 It's pulverizing the ice molecules in its atmosphere 252 00:12:36,188 --> 00:12:38,189 and blowing them out into space, 253 00:12:38,290 --> 00:12:40,291 and the ice molecules are streaming behind 254 00:12:40,392 --> 00:12:42,293 the planet like the tail of a comet. 255 00:12:42,394 --> 00:12:45,230 ROWE: The icy planet loses mass at 256 00:12:45,331 --> 00:12:49,033 a rate of over 500,000 tons per second. 257 00:12:49,135 --> 00:12:52,670 That's the equivalent of 300 aircraft carriers 258 00:12:52,772 --> 00:12:55,240 every minute. - CHRISTIANSEN: It sounds like 259 00:12:55,341 --> 00:12:56,741 that could be curtains for the planet. 260 00:12:56,842 --> 00:12:59,177 But remember, the planet is large, 261 00:12:59,278 --> 00:13:02,247 and the star is cooling down. - SHIELDS: As it cools, 262 00:13:02,348 --> 00:13:04,983 it will stop blasting the planet so intently, 263 00:13:05,084 --> 00:13:07,018 and that stream of gas will cease. 264 00:13:07,119 --> 00:13:08,686 The planet will probably end up losing 265 00:13:08,788 --> 00:13:11,723 only a few percent of its total mass. 266 00:13:11,824 --> 00:13:13,491 ROWE: So the planet should survive 267 00:13:13,592 --> 00:13:16,828 and continue orbiting the white dwarf. 268 00:13:16,929 --> 00:13:18,897 But a mystery remains. 269 00:13:18,998 --> 00:13:22,066 Why didn't the closely orbiting planet die 270 00:13:22,168 --> 00:13:25,670 when the star swelled to a red giant? 271 00:13:25,771 --> 00:13:30,775 SHIELDS: It had to have started farther out and moved inwards. 272 00:13:30,876 --> 00:13:34,145 Our best guess is that other ice giants were probably 273 00:13:34,246 --> 00:13:36,314 lurking somewhere in the outer regions 274 00:13:36,415 --> 00:13:39,050 of the system and knocked that planet inwards, 275 00:13:39,151 --> 00:13:42,120 towards the white dwarf, sometime after the red giant 276 00:13:42,221 --> 00:13:45,390 phase in some kind of cosmic pool game, 277 00:13:45,491 --> 00:13:46,591 if you will. 278 00:13:47,693 --> 00:13:50,428 ROWE: This isn't the only white dwarf with evidence of planets. 279 00:13:50,529 --> 00:13:54,032 About 570 light-years from Earth, 280 00:13:54,133 --> 00:13:59,671 there's a white dwarf star called WD 1145+017. 281 00:14:01,807 --> 00:14:04,209 After studying the star for five years, 282 00:14:04,310 --> 00:14:08,046 researchers report that the white dwarf is ripping apart 283 00:14:08,147 --> 00:14:11,316 and eating a mini rocky planet. 284 00:14:11,417 --> 00:14:13,218 CHRISTIANSEN: So as the planet is being torn up, 285 00:14:13,319 --> 00:14:16,221 we see this huge cloud of dust blocking out 50% of 286 00:14:16,322 --> 00:14:18,623 the light of the star and huge chunks of rock 287 00:14:18,724 --> 00:14:20,625 passing in front of the star. 288 00:14:20,726 --> 00:14:24,262 BYWATERS: It's exciting to see this planet being torn apart, 289 00:14:24,363 --> 00:14:27,532 because it's not often that we get to see an event, 290 00:14:27,633 --> 00:14:29,734 we get to see something in the process 291 00:14:29,835 --> 00:14:32,003 that we can observe and we can learn from. 292 00:14:34,773 --> 00:14:36,341 ROWE: There's more and more evidence 293 00:14:36,442 --> 00:14:38,409 that planetary systems can survive 294 00:14:38,510 --> 00:14:42,881 the death of their star and the formation of a white dwarf. 295 00:14:42,982 --> 00:14:45,884 It just depends on the planet's composition 296 00:14:45,985 --> 00:14:47,352 and location. 297 00:14:47,453 --> 00:14:51,589 The distance from the planet to the star is a critical factor, 298 00:14:51,690 --> 00:14:55,460 because as you move farther and farther out from a star, 299 00:14:55,561 --> 00:14:59,597 the intensity of that solar radiation decreases. 300 00:14:59,698 --> 00:15:02,667 So the farther you go out, the less heat you have, 301 00:15:02,768 --> 00:15:05,536 the less high-energy particles are reaching the surface of 302 00:15:05,638 --> 00:15:07,372 that planet. 303 00:15:07,473 --> 00:15:11,075 Also, rocky planets can survive better than gas giants, 304 00:15:11,176 --> 00:15:13,311 because rocky planets can hold onto their stuff better, 305 00:15:13,412 --> 00:15:15,647 whereas gas can be blown away much more easily. 306 00:15:17,816 --> 00:15:19,083 ROWE: These new discoveries raise 307 00:15:19,184 --> 00:15:21,920 questions about habitability around stars. 308 00:15:23,389 --> 00:15:26,824 Could white dwarf systems support life? 309 00:15:26,892 --> 00:15:28,960 SHIELDS: If we limit ourselves to only looking 310 00:15:29,061 --> 00:15:31,896 for life on planets orbiting stars like our sun, 311 00:15:31,997 --> 00:15:35,199 we would be doing ourselves a huge disservice. 312 00:15:35,267 --> 00:15:39,070 Far more important is to look for, around whatever star, 313 00:15:39,171 --> 00:15:40,872 the habitable zone, 314 00:15:40,973 --> 00:15:43,875 the Goldilocks zone, the region around a star where 315 00:15:43,976 --> 00:15:46,511 a planet could support life. 316 00:15:48,280 --> 00:15:50,148 ROWE: When it comes to supporting life, 317 00:15:50,249 --> 00:15:53,918 white dwarfs have some surprising advantages. 318 00:15:54,019 --> 00:15:55,920 CHRISTIANSEN: Even though there's no fusion happening, 319 00:15:56,021 --> 00:15:58,423 they have all of this internal energy stored up that they 320 00:15:58,524 --> 00:16:01,459 release that warms the nearby planets. 321 00:16:01,560 --> 00:16:04,762 SUTTER: Life might even prefer hanging out around 322 00:16:04,863 --> 00:16:06,264 a white dwarf, because 323 00:16:06,365 --> 00:16:08,533 it doesn't change much over the course 324 00:16:08,634 --> 00:16:10,168 of billions of years. 325 00:16:10,269 --> 00:16:13,705 With something like our sun, there are flares and coronal 326 00:16:13,806 --> 00:16:16,240 mass ejections, and then eventually, it's gonna die, 327 00:16:16,342 --> 00:16:17,942 and we have to deal with that. 328 00:16:18,043 --> 00:16:19,844 That's not a problem with a white dwarf. 329 00:16:21,113 --> 00:16:23,748 So if life can gain a foothold, 330 00:16:23,849 --> 00:16:25,883 it has a nice, stable home. 331 00:16:27,953 --> 00:16:30,888 ROWE: We now think 25 to 50% of 332 00:16:30,990 --> 00:16:33,558 white dwarfs have planetary systems. 333 00:16:33,659 --> 00:16:36,094 Perhaps one day, we'll find one with 334 00:16:36,195 --> 00:16:40,331 an Earth-like planet, and maybe even life. 335 00:16:42,067 --> 00:16:45,003 But not all of these tough little stars are good hosts. 336 00:16:46,472 --> 00:16:49,674 White dwarfs have a volatile nature. 337 00:16:49,775 --> 00:16:53,177 They can explode in some of the biggest bangs in the cosmos. 338 00:16:53,278 --> 00:16:56,280 [explosion blasts] 339 00:17:08,260 --> 00:17:12,063 ROWE: White dwarfs are the dead remains of stars like the sun. 340 00:17:13,532 --> 00:17:16,067 Most of these zombie stars slowly 341 00:17:16,168 --> 00:17:18,236 cooled down over billions of years. 342 00:17:20,406 --> 00:17:22,106 Most, but not all. 343 00:17:25,744 --> 00:17:28,546 Some go out in a spectacular explosion known 344 00:17:28,647 --> 00:17:30,314 as a type 1a supernova. 345 00:17:31,917 --> 00:17:33,351 A type 1a supernova 346 00:17:33,452 --> 00:17:35,753 is one of the most violent, powerful, 347 00:17:35,854 --> 00:17:38,089 energetic events in the universe. 348 00:17:38,190 --> 00:17:41,125 We are talking about a star exploding. 349 00:17:41,226 --> 00:17:43,594 They can outshine entire galaxies. 350 00:17:43,695 --> 00:17:45,663 They can create devastation over 351 00:17:45,764 --> 00:17:47,465 hundreds and hundreds of light-years. 352 00:17:47,566 --> 00:17:49,000 They're a big deal. 353 00:17:51,670 --> 00:17:54,405 ROWE: We'd seen the aftermath of these cosmic fireworks, 354 00:17:54,506 --> 00:17:57,542 but for over 60 years, we had little direct evidence 355 00:17:57,643 --> 00:17:59,310 they came from white dwarfs. 356 00:18:01,613 --> 00:18:05,583 Then students from University College London UK got lucky. 357 00:18:05,684 --> 00:18:09,587 While taking routine photographs, 358 00:18:09,688 --> 00:18:11,889 they spotted a supernova explosion 359 00:18:11,990 --> 00:18:14,792 in our own cosmic neighborhood. 360 00:18:14,893 --> 00:18:17,895 PLAIT: M82, the cigar galaxy, is actually really 361 00:18:17,996 --> 00:18:19,964 close to us on cosmic terms. 362 00:18:20,065 --> 00:18:22,533 It's only about 12 million light-years away. 363 00:18:22,634 --> 00:18:25,336 This makes it one of the closest galaxies in the sky. 364 00:18:26,505 --> 00:18:29,273 The blast called Supernova 2014J was 365 00:18:29,374 --> 00:18:33,244 the closest type 1a supernova for over 20 years. 366 00:18:34,413 --> 00:18:36,247 Its proximity allowed us to look for 367 00:18:36,348 --> 00:18:40,017 the signature of a white dwarf supernova, 368 00:18:40,119 --> 00:18:42,019 a blast of gamma rays. 369 00:18:42,121 --> 00:18:47,125 Gamma rays are a type of light that's incredibly energetic. 370 00:18:47,226 --> 00:18:49,760 They're the most energetic type of rays, 371 00:18:49,862 --> 00:18:53,498 or photons, on the electromagnetic spectrum. 372 00:18:53,599 --> 00:18:55,099 ROWE: White dwarfs should release 373 00:18:55,200 --> 00:18:57,568 gamma rays when they explode. 374 00:18:57,669 --> 00:19:01,239 But dust in interstellar space soaks up the rays, 375 00:19:01,340 --> 00:19:06,244 so unless an explosion is close by, they're hard to detect. 376 00:19:06,345 --> 00:19:09,447 For years, astronomers had been looking for the gamma rays 377 00:19:09,548 --> 00:19:12,116 that should be emitted by a type 1a supernova, 378 00:19:12,217 --> 00:19:13,584 but no one had found them. 379 00:19:15,954 --> 00:19:18,022 ROWE: Now, scientists had their chance 380 00:19:18,123 --> 00:19:20,758 and the technology to see the elusive rays. 381 00:19:22,628 --> 00:19:24,795 Using ISA's integral satellite, 382 00:19:24,897 --> 00:19:26,931 they sifted through the shockwaves sent out by 383 00:19:27,032 --> 00:19:29,500 the explosion in M82. 384 00:19:29,601 --> 00:19:32,537 It was tough, but finally, they got a reading, 385 00:19:32,638 --> 00:19:35,306 the telltale signal of gamma rays. 386 00:19:35,407 --> 00:19:38,276 It's the best evidence yet for white dwarfs 387 00:19:38,377 --> 00:19:41,412 exploding in type 1a supernovas. 388 00:19:41,513 --> 00:19:46,484 The reason Supernova 2014J was so cool is that this 389 00:19:46,585 --> 00:19:49,587 observation gave scientists evidence, it's white dwarfs that 390 00:19:49,688 --> 00:19:53,124 explode to create this specific type of supernova. 391 00:19:53,225 --> 00:19:55,660 ROWE: So which white dwarfs fade out 392 00:19:55,761 --> 00:19:57,828 and which ones go out with a bang? 393 00:20:00,799 --> 00:20:02,633 A survey of stars revealed 394 00:20:02,734 --> 00:20:07,271 around 30% of white dwarfs live in binary systems, 395 00:20:07,372 --> 00:20:09,907 but white dwarfs are not good neighbors. 396 00:20:10,008 --> 00:20:13,811 A white dwarf in a binary system is... it's like a zombie. 397 00:20:13,912 --> 00:20:16,681 It's the corpse of a star that used to be alive. 398 00:20:16,782 --> 00:20:18,716 But now it is eating the material 399 00:20:18,817 --> 00:20:21,185 from a star that is still alive. 400 00:20:21,286 --> 00:20:23,854 They very literally suck the material 401 00:20:23,956 --> 00:20:25,690 and suck the life out of that star 402 00:20:25,791 --> 00:20:28,392 by swallowing up all of its outer layers. 403 00:20:30,062 --> 00:20:32,697 ROWE: The white dwarf zombie tendencies can backfire. 404 00:20:33,865 --> 00:20:36,834 Adding mass to a white dwarf is like this. 405 00:20:36,935 --> 00:20:41,672 We keep adding mass from that companion star 406 00:20:41,773 --> 00:20:45,343 a little bit of hydrogen at a time, 407 00:20:45,444 --> 00:20:48,946 building up that atmosphere, and for a long time, 408 00:20:49,047 --> 00:20:50,748 everything's fine. 409 00:20:50,849 --> 00:20:54,785 Until you add too much mass, and you reach that critical 410 00:20:54,886 --> 00:20:57,054 threshold, and then... 411 00:21:00,459 --> 00:21:02,493 ROWE: The real-world consequences of 412 00:21:02,594 --> 00:21:05,896 reaching the threshold are devastating. 413 00:21:05,998 --> 00:21:09,600 The extra weight of gas stolen from the companion star 414 00:21:09,701 --> 00:21:12,703 compresses carbon deep in the core of the white dwarf. 415 00:21:14,473 --> 00:21:18,409 When the white dwarf reaches 1.4 times the mass of our sun, 416 00:21:18,510 --> 00:21:23,080 it hits a tipping point known as the Chandrasekhar limit. 417 00:21:23,181 --> 00:21:25,616 You add up the mass little by little by little until 418 00:21:25,717 --> 00:21:28,119 you get to that Chandrasekhar limit and then blam, 419 00:21:28,220 --> 00:21:30,421 there's a supernova. - ROWE: In a flash, 420 00:21:30,522 --> 00:21:32,990 carbon undergoes nuclear fusion, 421 00:21:33,091 --> 00:21:34,992 releasing a tremendous amount of energy. 422 00:21:38,063 --> 00:21:39,563 FILIPPENKO: If the white dwarf explodes 423 00:21:39,665 --> 00:21:41,132 at the Chandrasekhar limit, 424 00:21:41,233 --> 00:21:43,901 it's a little bit like fireworks that all have 425 00:21:44,002 --> 00:21:45,670 the same amount of gunpowder. 426 00:21:45,771 --> 00:21:49,106 They'll all go off in the same way, they'll be equally loud. 427 00:21:49,207 --> 00:21:51,275 Well, the supernovas will be equally bright. 428 00:21:53,045 --> 00:21:55,279 ROWE: This equal brightness of all type 1a 429 00:21:55,380 --> 00:21:58,549 supernovas is vital to our understanding of space. 430 00:21:59,751 --> 00:22:03,321 Type 1a's are known as standard candles 431 00:22:03,422 --> 00:22:05,923 and are useful tools for calculating fast 432 00:22:06,024 --> 00:22:07,925 cosmic distances. 433 00:22:08,026 --> 00:22:10,161 They were the key to the Nobel Prize winning 434 00:22:10,262 --> 00:22:12,897 discovery that the expansion of our universe 435 00:22:12,998 --> 00:22:14,465 is accelerating. 436 00:22:14,566 --> 00:22:20,271 But what kind of companion star triggers type 1a supernovas? 437 00:22:20,372 --> 00:22:25,176 For decades, the number one suspect was red giant stars. 438 00:22:25,277 --> 00:22:26,410 HOPKINS: A red giant's 439 00:22:26,511 --> 00:22:30,314 a good candidate, because it's a very big, puffy star. 440 00:22:30,415 --> 00:22:33,617 That material becomes easy pickings for the white dwarf 441 00:22:33,719 --> 00:22:36,520 to siphon off until it gets big enough to explode. 442 00:22:37,889 --> 00:22:40,024 ROWE: To prove the theory, we needed to find 443 00:22:40,125 --> 00:22:43,961 evidence in the debris left behind after a supernova. 444 00:22:44,062 --> 00:22:47,331 Stars are surprisingly hardy objects. 445 00:22:47,432 --> 00:22:50,735 They can survive an explosion of a nearby star. 446 00:22:50,836 --> 00:22:53,237 Some of these companion stars should still be there. 447 00:22:53,338 --> 00:22:55,539 A lot of them will be, you know, worse for the wear, 448 00:22:55,640 --> 00:22:57,742 but they'll still exist. 449 00:22:57,843 --> 00:22:59,677 ROWE: Scientists search through the remains 450 00:22:59,778 --> 00:23:02,546 of 70 type 1a supernovas. 451 00:23:03,915 --> 00:23:05,850 Only one blast zone contained 452 00:23:05,951 --> 00:23:08,619 the glowing remains of a red giant. 453 00:23:09,721 --> 00:23:12,923 The fact that we've only found maybe this one example suggests 454 00:23:13,024 --> 00:23:15,192 that actually, they're not quite the serial killers 455 00:23:15,293 --> 00:23:16,694 we thought. 456 00:23:16,795 --> 00:23:18,863 It's probably likely that this is 457 00:23:18,964 --> 00:23:22,767 the minority of these types of supernova explosions. 458 00:23:22,868 --> 00:23:26,303 Indeed, we now think that only a small fraction of 459 00:23:26,405 --> 00:23:30,374 these white dwarf supernovas involve a red giant, 460 00:23:30,475 --> 00:23:33,210 despite the fact that, in the standard textbooks, for 461 00:23:33,311 --> 00:23:36,080 decades, that was the preferred explanation. 462 00:23:37,382 --> 00:23:38,783 ROWE: If red giants don't cause 463 00:23:38,884 --> 00:23:41,619 the majority of type 1a supernovas, 464 00:23:41,720 --> 00:23:43,487 what does? 465 00:23:43,588 --> 00:23:45,122 New evidence suggests 466 00:23:45,223 --> 00:23:47,024 colliding white dwarfs, 467 00:23:47,125 --> 00:23:49,326 star mergers that could exceed 468 00:23:49,428 --> 00:23:51,162 the Chandrasekhar limit, 469 00:23:51,263 --> 00:23:54,365 producing explosions with different brightness. 470 00:23:54,466 --> 00:23:57,168 But if the explosions vary in brightness, 471 00:23:57,269 --> 00:23:58,969 can they still be used 472 00:23:59,070 --> 00:24:01,205 as standard candles? 473 00:24:01,306 --> 00:24:04,475 PONTZEN: If we don't really know what a type 1a supernova is, 474 00:24:04,576 --> 00:24:05,976 then when we use them to map out 475 00:24:06,077 --> 00:24:08,979 the universe and the way the universe is expanding, 476 00:24:09,080 --> 00:24:12,450 we just can't be sure any longer what it is we're looking at. 477 00:24:12,551 --> 00:24:14,084 If we're wrong about that, 478 00:24:14,186 --> 00:24:16,887 then we're wrong about so many other things that our whole 479 00:24:16,988 --> 00:24:18,456 model of the universe falls apart. 480 00:24:19,524 --> 00:24:22,626 ROWE: Is our understanding of the cosmos completely wrong? 481 00:24:35,974 --> 00:24:39,944 ROWE: White dwarfs explode in spectacular type 1a supernovas. 482 00:24:41,480 --> 00:24:44,215 They're a crucial tool for measuring the universe, 483 00:24:44,316 --> 00:24:46,150 but there is a problem. 484 00:24:48,086 --> 00:24:50,321 The standard model says that white dwarfs 485 00:24:50,422 --> 00:24:54,258 gradually steal mass from a red giant star 486 00:24:54,359 --> 00:24:56,160 until they reach a tipping point 487 00:24:56,261 --> 00:24:57,895 called the Chandrasekhar limit. 488 00:25:00,632 --> 00:25:03,601 But recent observations proved this doesn't explain 489 00:25:03,702 --> 00:25:06,337 how most type 1a supernovas occur. 490 00:25:07,906 --> 00:25:12,009 The majority of type 1a explosions remain a mystery. 491 00:25:12,110 --> 00:25:14,678 We call the explosions from white dwarfs standard candles, 492 00:25:14,779 --> 00:25:16,013 but they're really not that standard. 493 00:25:16,114 --> 00:25:18,582 We actually think there's different types of explosions. 494 00:25:18,683 --> 00:25:21,218 THALLER: It may be imperative to our understanding 495 00:25:21,319 --> 00:25:23,153 of the entire universe that we really get 496 00:25:23,255 --> 00:25:25,689 this straight, because the reason we think 497 00:25:25,790 --> 00:25:27,958 the expansion rate of the universe is accelerating 498 00:25:28,059 --> 00:25:30,394 is based on the brightness of type 1 supernovas 499 00:25:30,495 --> 00:25:33,898 all being the same, and maybe that's not the case. 500 00:25:33,999 --> 00:25:36,667 ROWE: Researchers suspected a theoretical type of 501 00:25:36,768 --> 00:25:38,502 merger could be responsible 502 00:25:38,603 --> 00:25:42,006 for more type 1a supernovas, 503 00:25:42,073 --> 00:25:45,776 the result of two white dwarfs crashing together. 504 00:25:45,877 --> 00:25:48,779 But this messes with the math. 505 00:25:48,880 --> 00:25:51,916 The Chandrasekhar limit says white dwarfs should 506 00:25:52,017 --> 00:25:53,150 explode when they reach 507 00:25:53,251 --> 00:25:56,687 1.4 times the mass of our sun. 508 00:25:56,788 --> 00:26:00,024 Two white dwarfs colliding can exceed this mass, 509 00:26:00,125 --> 00:26:02,526 and more mass means a bigger bang 510 00:26:02,594 --> 00:26:05,129 and a brighter explosion. 511 00:26:07,432 --> 00:26:08,332 You're not adding gas 512 00:26:08,433 --> 00:26:10,034 little by little, you're adding a whole 513 00:26:10,135 --> 00:26:12,369 other white dwarf... That will go off. 514 00:26:12,470 --> 00:26:14,138 It will look like a type 1 supernova, 515 00:26:14,239 --> 00:26:15,673 but it won't be the standard candle. 516 00:26:15,774 --> 00:26:17,308 It'll be brighter than we expect. 517 00:26:17,409 --> 00:26:22,446 ROWE: But no white dwarf mergers have been found, because 518 00:26:22,547 --> 00:26:26,617 detecting one after it happens is virtually impossible. 519 00:26:26,718 --> 00:26:28,819 HOPKINS: If two white dwarfs merge together, 520 00:26:28,920 --> 00:26:32,356 it's almost impossible to tell, because the DNA of the two 521 00:26:32,457 --> 00:26:35,259 systems is all mixed together, and it's all identical. 522 00:26:35,327 --> 00:26:38,395 You can't tell that there was a separate companion in 523 00:26:38,496 --> 00:26:39,697 the first place. 524 00:26:39,798 --> 00:26:42,600 SUTTER: So we can't just look at when there's a bright flash. 525 00:26:42,701 --> 00:26:44,935 We have to go look for the ticking time bombs in 526 00:26:45,036 --> 00:26:46,570 the galaxy. 527 00:26:46,671 --> 00:26:50,140 ROWE: Astronomers investigating a strange shaped 528 00:26:50,241 --> 00:26:52,876 cloud of gas made a breakthrough. 529 00:26:52,978 --> 00:26:56,814 Using ESO's Very Large Telescope, 530 00:26:56,915 --> 00:27:02,252 they focused in on a planetary nebula called Henize 2-428. 531 00:27:02,354 --> 00:27:05,522 Planetary nebulas are normally symmetric, 532 00:27:05,624 --> 00:27:07,191 because red giants shed 533 00:27:07,292 --> 00:27:11,328 their outer layers evenly as they become white dwarfs. 534 00:27:11,429 --> 00:27:14,198 But this one is lopsided. 535 00:27:14,299 --> 00:27:16,934 We think, in this case, there might be the presence of 536 00:27:17,035 --> 00:27:21,538 a companion star that shapes and twists and sculpts 537 00:27:21,640 --> 00:27:23,540 that planetary nebula. 538 00:27:25,610 --> 00:27:26,844 ROWE: Researchers peeled back 539 00:27:26,945 --> 00:27:30,614 the gaseous layers and discovered something shocking, 540 00:27:30,715 --> 00:27:33,717 a two-star system made up of 541 00:27:33,818 --> 00:27:36,420 the most massive orbiting white dwarf pair 542 00:27:36,521 --> 00:27:37,621 ever discovered. 543 00:27:39,591 --> 00:27:43,527 Each star is 90% as massive as our sun, 544 00:27:43,628 --> 00:27:45,295 and they're so close together, they take 545 00:27:45,397 --> 00:27:47,331 just four hours to orbit each other. 546 00:27:47,432 --> 00:27:50,668 And they're getting closer. 547 00:27:50,769 --> 00:27:54,838 SUTTER: If you've ever seen a car crash about to happen, 548 00:27:54,939 --> 00:27:58,175 you know that sense of inevitability 549 00:27:58,276 --> 00:27:59,677 as you witness that. 550 00:27:59,778 --> 00:28:01,745 That's what we're seeing in this system. 551 00:28:01,846 --> 00:28:06,083 We see these two massive white dwarfs spiraling closer 552 00:28:06,184 --> 00:28:10,954 and closer and closer, and we know that disaster is coming. 553 00:28:11,056 --> 00:28:12,990 ROWE: In around 700 million years, 554 00:28:13,091 --> 00:28:15,392 these stars will merge and explode 555 00:28:15,493 --> 00:28:17,661 in a type 1a supernova. 556 00:28:22,200 --> 00:28:24,768 Now, thanks to the discovery of more systems 557 00:28:24,869 --> 00:28:26,637 like Henize 2-428, 558 00:28:26,738 --> 00:28:29,406 we think white dwarf collisions could be responsible 559 00:28:29,507 --> 00:28:32,176 for the majority of type 1a supernovas. 560 00:28:32,277 --> 00:28:34,511 [explosion blasts] 561 00:28:34,612 --> 00:28:38,182 Two white dwarfs can merge together. 562 00:28:38,283 --> 00:28:40,584 And if the sum of their masses is greater than 563 00:28:40,685 --> 00:28:42,152 1.4 solar masses, 564 00:28:42,287 --> 00:28:44,288 then you can get a Super-Chandra type 1a. 565 00:28:44,389 --> 00:28:46,824 ROWE: We've now observed 566 00:28:46,925 --> 00:28:48,859 nine Super-Chandra explosions, 567 00:28:50,495 --> 00:28:52,196 and to complicate matters further, 568 00:28:52,297 --> 00:28:55,966 we've spotted another form of white dwarf supernovas, 569 00:28:56,067 --> 00:28:58,001 Sub-Chandra type 1as. 570 00:28:59,871 --> 00:29:03,173 These mysterious white dwarfs that we don't quite understand 571 00:29:03,274 --> 00:29:06,677 die off much quicker than regular white dwarf supernovas. 572 00:29:06,811 --> 00:29:08,445 [explosion blasts] 573 00:29:08,546 --> 00:29:10,814 ROWE: The explosions are less violent than normal 574 00:29:10,915 --> 00:29:14,017 type 1a supernovas and fade away faster. 575 00:29:14,119 --> 00:29:16,386 But we don't know why. 576 00:29:18,256 --> 00:29:19,957 Maybe it has something to do with 577 00:29:20,058 --> 00:29:22,292 the properties of the star or the rotation, 578 00:29:22,393 --> 00:29:24,595 but the Chandrasekhar limit may not be so exact. 579 00:29:24,696 --> 00:29:27,197 It's kind of a Chandrasekhar range. 580 00:29:27,298 --> 00:29:30,134 The physics textbooks are now being sort of rewritten, 581 00:29:30,235 --> 00:29:34,538 or at least modified, because we know that not all type 1a 582 00:29:34,639 --> 00:29:38,008 supernovas come from Chandra mass white dwarfs. 583 00:29:38,109 --> 00:29:41,979 There's actually a variety of type 1a supernovas, 584 00:29:42,080 --> 00:29:46,350 a variety of white dwarf masses and configurations 585 00:29:46,451 --> 00:29:47,618 that can explode. 586 00:29:49,120 --> 00:29:52,189 ROWE: These new discoveries mean researchers now study 587 00:29:52,290 --> 00:29:55,359 the chemistry and duration of type 1a supernovas, 588 00:29:55,460 --> 00:29:57,327 not just their brightness. 589 00:30:01,099 --> 00:30:05,068 The deeper we investigate, the more mysteries we uncover, 590 00:30:05,170 --> 00:30:08,772 like rogue white dwarfs streaking across the galaxy 591 00:30:08,873 --> 00:30:13,977 and tiny stars that explode over and over again. 592 00:30:14,078 --> 00:30:16,479 Can these odd white dwarfs shed more 593 00:30:16,548 --> 00:30:19,616 light on the mystery of type 1a supernovas? 594 00:30:30,562 --> 00:30:31,461 ROWE: White dwarfs are 595 00:30:31,563 --> 00:30:33,797 surprisingly difficult to understand. 596 00:30:35,600 --> 00:30:38,468 They behave in completely unexpected ways. 597 00:30:40,238 --> 00:30:43,173 But these oddballs may help answer 598 00:30:43,241 --> 00:30:46,844 the remaining questions about type 1a supernovas. 599 00:30:46,945 --> 00:30:49,213 These are white dwarfs, but not as we know them. 600 00:30:50,448 --> 00:30:55,385 ROWE: 2017... astronomers spot a rebellious star 601 00:30:55,486 --> 00:30:57,855 raising hell in the Little Dipper constellation. 602 00:30:59,624 --> 00:31:02,459 It's like a zombie, but this isn't one shambling down 603 00:31:02,560 --> 00:31:04,828 the road, it runs like Usain Bolt. 604 00:31:04,929 --> 00:31:07,598 This thing is screaming through the galaxy at a much 605 00:31:07,699 --> 00:31:10,000 higher speed than you'd expect for a star like it. 606 00:31:12,070 --> 00:31:15,138 ROWE: The white dwarf called LP 40-365 607 00:31:15,240 --> 00:31:16,974 is moving incredibly fast 608 00:31:17,075 --> 00:31:18,675 towards the edge of the Milky Way. 609 00:31:18,776 --> 00:31:24,281 It's not the only star behaving oddly... in 2019, 610 00:31:24,382 --> 00:31:27,384 we spotted three more white dwarfs racing across 611 00:31:27,485 --> 00:31:28,852 the galaxy. 612 00:31:28,953 --> 00:31:30,854 Finding one white dwarf blasting its way 613 00:31:30,955 --> 00:31:32,656 through space is weird enough. 614 00:31:32,757 --> 00:31:35,692 But to find three more, that's telling you that something is 615 00:31:35,793 --> 00:31:37,194 going on, and whatever it is 616 00:31:37,295 --> 00:31:40,063 that's going on happens a lot. 617 00:31:40,164 --> 00:31:41,832 ROWE: So what sent these renegades 618 00:31:41,933 --> 00:31:44,101 racing across the galaxy? 619 00:31:44,202 --> 00:31:47,971 LP 40-365 and these other weird white dwarfs 620 00:31:48,072 --> 00:31:51,074 could be the results of failed supernovas. 621 00:31:51,175 --> 00:31:52,910 People have theorized that maybe 622 00:31:53,011 --> 00:31:54,978 these things didn't finish exploding. 623 00:31:55,079 --> 00:31:56,313 And if so, we should find 624 00:31:56,414 --> 00:31:59,449 some unburnt fractions wandering around the galaxy. 625 00:32:01,052 --> 00:32:04,621 ROWE: In the last 20 years, we've spotted some unusually dim 626 00:32:04,722 --> 00:32:07,057 supernovas that could have sent 627 00:32:07,158 --> 00:32:11,194 LP 40-365 and friends flying. 628 00:32:11,296 --> 00:32:14,932 So what looks like happened is that in a binary pair, 629 00:32:15,033 --> 00:32:16,934 there was stuff dumping onto a white dwarf, 630 00:32:17,035 --> 00:32:19,569 and we were about to have a type 1 supernova. 631 00:32:19,671 --> 00:32:22,606 But the type 1 supernova didn't go off symmetrically. 632 00:32:22,707 --> 00:32:25,876 Some of it actually exploded, and some of it didn't. 633 00:32:25,977 --> 00:32:29,246 That energy didn't go out in all directions. 634 00:32:29,347 --> 00:32:31,949 And one of the things that occurred is that these stars 635 00:32:32,050 --> 00:32:35,252 got sent hurling across space at these incredible speeds. 636 00:32:39,190 --> 00:32:42,059 ROWE: We call them type 1ax supernovas. 637 00:32:42,160 --> 00:32:45,696 They could make up between 10 and 30% 638 00:32:45,797 --> 00:32:48,265 of type 1a supernovas. 639 00:32:48,366 --> 00:32:50,867 Many could throw out a runaway star. 640 00:32:52,437 --> 00:32:55,839 But we still don't know why the supernova fails. 641 00:32:55,940 --> 00:32:58,976 PLAIT: A funny thing about science is things 642 00:32:59,077 --> 00:33:02,112 that fail still teach you what's going on. 643 00:33:02,213 --> 00:33:04,548 Why are these ones different? Were they not massive enough? 644 00:33:04,649 --> 00:33:06,683 Where they too massive? Was the companion star 645 00:33:06,784 --> 00:33:08,885 not feeding them the material the right way? 646 00:33:08,987 --> 00:33:11,655 Something happened there to make these stars 647 00:33:11,756 --> 00:33:14,925 not basically blow themselves to bits. 648 00:33:15,026 --> 00:33:17,060 And that's telling us something about 649 00:33:17,161 --> 00:33:19,830 the way type 1as do explode. 650 00:33:21,499 --> 00:33:23,800 ROWE: It seems that life in a binary star system 651 00:33:23,901 --> 00:33:25,902 can be rough for white dwarfs, 652 00:33:26,004 --> 00:33:29,239 but for some lucky stars, their lives can 653 00:33:29,340 --> 00:33:31,174 be more mellow. 654 00:33:31,275 --> 00:33:33,377 Just because a white dwarf 655 00:33:33,478 --> 00:33:35,278 has a normal star companion that 656 00:33:35,380 --> 00:33:38,815 it's stealing material from does not spell a death sentence 657 00:33:38,916 --> 00:33:40,217 for that white dwarf. 658 00:33:40,318 --> 00:33:43,253 ROWE: February 2013. 659 00:33:43,354 --> 00:33:46,757 Astronomers discover a star in the Andromeda galaxy 660 00:33:46,858 --> 00:33:50,961 that flashes over and over and over again. 661 00:33:51,062 --> 00:33:52,129 With each flare, 662 00:33:52,230 --> 00:33:55,932 it shines a million times brighter than our sun 663 00:33:56,034 --> 00:33:58,268 before dimming to its normal state. 664 00:33:58,369 --> 00:34:03,340 It's called M31N 2018-12a. 665 00:34:06,110 --> 00:34:09,413 This is not a supernova, it's its little sibling, 666 00:34:09,514 --> 00:34:10,914 a nova. 667 00:34:11,015 --> 00:34:13,583 But what's weird about this one is that it happens 668 00:34:13,684 --> 00:34:14,851 every year. 669 00:34:14,952 --> 00:34:18,488 Astronomers have known for a long time that there are these 670 00:34:18,589 --> 00:34:21,358 cases of these nova that go off, 671 00:34:21,459 --> 00:34:23,360 you know, somewhat regularly, every 10 years, 672 00:34:23,461 --> 00:34:24,661 every 100 years. 673 00:34:24,762 --> 00:34:26,396 But finding one that goes off 674 00:34:26,497 --> 00:34:29,032 every year is a remarkable discovery. 675 00:34:30,568 --> 00:34:31,968 ROWE: Much like supernovas, 676 00:34:32,070 --> 00:34:34,237 novas occur in a close binary system, 677 00:34:34,338 --> 00:34:37,274 where a white dwarf and another star orbit each other. 678 00:34:39,944 --> 00:34:41,812 The white dwarf pulls in hydrogen 679 00:34:41,913 --> 00:34:43,680 from the companion star. 680 00:34:43,781 --> 00:34:46,149 The gas falls onto its surface. 681 00:34:46,250 --> 00:34:48,718 And so as that hydrogen piles up, 682 00:34:48,820 --> 00:34:50,921 eventually, it gets to the point where 683 00:34:51,022 --> 00:34:54,191 it can fuse into helium and goes bang. 684 00:34:55,960 --> 00:34:56,860 ROWE: In supernovas, 685 00:34:56,961 --> 00:35:00,163 fusion happens deep inside the star's core, 686 00:35:01,532 --> 00:35:05,335 but in novas, fusion only occurs on the surface. 687 00:35:05,403 --> 00:35:09,406 An explosion flares across the white dwarf's exterior, 688 00:35:09,507 --> 00:35:13,510 hurling unburned hydrogen out into space. 689 00:35:13,611 --> 00:35:17,647 The result... an object called a remnant. 690 00:35:17,715 --> 00:35:23,386 The remnant from Nova M31N is 400 light-years wide. 691 00:35:23,488 --> 00:35:25,122 This particular remnant is much 692 00:35:25,223 --> 00:35:27,891 bigger than even supernova remnants. 693 00:35:27,992 --> 00:35:29,526 It's much larger, much denser 694 00:35:29,627 --> 00:35:31,461 and brighter than most normal remnants are. 695 00:35:31,562 --> 00:35:32,562 But that makes sense 696 00:35:32,663 --> 00:35:34,798 if the star flares up so often. 697 00:35:34,899 --> 00:35:38,368 Think about the star flaring away for millions of years. 698 00:35:38,469 --> 00:35:42,572 You build up a gigantic nova remnant. 699 00:35:42,673 --> 00:35:44,107 ROWE: The repeating flares explain 700 00:35:44,208 --> 00:35:45,575 the huge size of the remnant. 701 00:35:45,676 --> 00:35:48,945 But why does the nova explode so frequently? 702 00:35:49,046 --> 00:35:53,183 Classically, we thought that when a nova went off 703 00:35:53,284 --> 00:35:54,384 on the surface of 704 00:35:54,485 --> 00:35:58,221 a white dwarf star that the white dwarf star's mass 705 00:35:58,322 --> 00:35:59,489 didn't change very much. 706 00:35:59,590 --> 00:36:01,291 Or maybe it got a little smaller. 707 00:36:01,392 --> 00:36:04,661 Now we think that after a nova, 708 00:36:04,762 --> 00:36:07,430 the white dwarf gains a bit of mass. 709 00:36:09,033 --> 00:36:12,736 ROWE: Recurrent novas, like M31N, steal more mass from 710 00:36:12,837 --> 00:36:15,906 their companion star than they blow off in each explosion. 711 00:36:17,108 --> 00:36:18,875 Some gain more and more mass, 712 00:36:18,976 --> 00:36:21,845 exploding more frequently until they reach 713 00:36:21,946 --> 00:36:23,980 the Chandrasekhar limit 714 00:36:24,081 --> 00:36:26,983 and go full-on supernova. 715 00:36:27,084 --> 00:36:29,486 M31N may very well be 716 00:36:29,587 --> 00:36:32,088 the missing link that shows us 717 00:36:32,190 --> 00:36:35,258 that some nova systems eventually become 718 00:36:35,359 --> 00:36:36,626 supernova systems. 719 00:36:36,727 --> 00:36:38,995 ROWE: Working out how novas become 720 00:36:39,096 --> 00:36:42,065 supernovas and why some supernovas fail 721 00:36:43,968 --> 00:36:47,671 might help us understand what makes white dwarfs explode. 722 00:36:50,474 --> 00:36:52,742 But just when we think we get a break, 723 00:36:52,843 --> 00:36:55,078 white dwarfs hit us with another bombshell... 724 00:36:55,179 --> 00:36:57,380 death rays. 725 00:37:09,727 --> 00:37:12,796 ROWE: White dwarfs can explode in violent supernovas, 726 00:37:15,733 --> 00:37:18,501 but that's not their only deadly trick. 727 00:37:18,603 --> 00:37:20,737 They might also create the most 728 00:37:20,838 --> 00:37:24,774 magnetic and terrifying beast in the universe... 729 00:37:24,875 --> 00:37:27,143 A magnetar. 730 00:37:27,245 --> 00:37:30,347 Magentars are scary. They just are. 731 00:37:30,448 --> 00:37:31,481 I mean, it's even in the name. 732 00:37:31,582 --> 00:37:33,883 The word magnetar sounds scary. 733 00:37:33,985 --> 00:37:35,452 They're the reigning champion of 734 00:37:35,553 --> 00:37:37,687 the largest magnetic field in the universe. 735 00:37:40,191 --> 00:37:44,828 SUTTER: The magnetic fields around magnetars are so strong 736 00:37:44,929 --> 00:37:48,965 that they can stretch and distort individual atoms. 737 00:37:49,066 --> 00:37:52,836 They can turn an atom into a long, thin pencil shape. 738 00:37:52,937 --> 00:37:56,339 Once you start stretching atoms out into this shape, 739 00:37:56,440 --> 00:37:59,676 they can't bond together in the usual ways anymore. 740 00:37:59,777 --> 00:38:01,411 And so you can just throw out 741 00:38:01,512 --> 00:38:04,514 every chemistry textbook in the world. 742 00:38:04,615 --> 00:38:06,850 BULLOCK: If an astronaut were unlucky enough to get close to 743 00:38:06,951 --> 00:38:08,318 a magnetar, say, within 744 00:38:08,419 --> 00:38:11,888 600, 700 miles, the whole body of the astronaut 745 00:38:11,989 --> 00:38:13,256 would be completely obliterated. 746 00:38:13,357 --> 00:38:15,625 They would more or less dissolve. 747 00:38:15,726 --> 00:38:18,495 ROWE: The origin of these fearsome creatures is a mystery, 748 00:38:18,596 --> 00:38:21,364 but it must be something very violent. 749 00:38:21,465 --> 00:38:24,567 We think they send out a clue as they form, 750 00:38:24,669 --> 00:38:28,738 powerful blasts of energy shooting across the cosmos. 751 00:38:28,839 --> 00:38:32,742 In the past few decades, we've noticed these very odd, 752 00:38:32,843 --> 00:38:35,211 very confusing and very brief 753 00:38:35,313 --> 00:38:39,549 flashes of intense radio energy. 754 00:38:39,650 --> 00:38:42,919 ROWE: They're known as fast radio bursts, or FRBs. 755 00:38:44,088 --> 00:38:46,990 Some FRBs don't repeat. They're one and done. 756 00:38:47,091 --> 00:38:48,892 So you're talking about an incredible amount 757 00:38:48,993 --> 00:38:51,428 of energy released in less than a second, 758 00:38:51,529 --> 00:38:52,862 then it's over. 759 00:38:52,963 --> 00:38:55,231 ROWE: Because these non-repeating FRBs are 760 00:38:55,333 --> 00:38:59,469 so powerful, we think they could come from a huge collision. 761 00:38:59,570 --> 00:39:02,238 The heavier and denser the objects colliding, 762 00:39:03,908 --> 00:39:05,008 the bigger the bang. 763 00:39:06,410 --> 00:39:10,447 New research suggests a white dwarf star hitting a dense, 764 00:39:10,548 --> 00:39:13,917 heavy neutron star could be enough to birth 765 00:39:14,018 --> 00:39:15,985 a magnetar, 766 00:39:16,087 --> 00:39:19,089 sending out FRBs in the process. 767 00:39:19,190 --> 00:39:22,592 A neutron star is like a white dwarf. 768 00:39:22,693 --> 00:39:26,096 Even more so... It is the leftover core 769 00:39:26,197 --> 00:39:28,365 of a giant star. 770 00:39:28,466 --> 00:39:31,134 They're effectively giant balls of neutrons 771 00:39:31,235 --> 00:39:32,168 squeezed together 772 00:39:32,269 --> 00:39:34,771 into things about the size of a city. 773 00:39:34,872 --> 00:39:37,774 SUTTER: You have a neutron star, an incredibly nasty, 774 00:39:37,875 --> 00:39:40,844 complicated exotic object and a white dwarf, 775 00:39:40,945 --> 00:39:43,546 an incredibly nasty, ugly, complicated object, 776 00:39:43,647 --> 00:39:45,882 crashing headlong into each other. 777 00:39:47,585 --> 00:39:49,719 ROWE: As the two stars orbit more closely, 778 00:39:49,820 --> 00:39:52,489 the neutron star strips gas from the white dwarf. 779 00:39:53,958 --> 00:39:57,727 This material spirals onto the neutron star, 780 00:39:57,795 --> 00:40:00,196 causing it to spin faster and faster. 781 00:40:02,633 --> 00:40:06,069 The rapid rotation amplifies its magnetic fields 782 00:40:07,438 --> 00:40:10,640 until the two stars collide, 783 00:40:10,741 --> 00:40:13,743 creating a very magnetic monster, 784 00:40:13,844 --> 00:40:15,745 a magnetar. 785 00:40:15,846 --> 00:40:17,680 It's a turbulent situation. 786 00:40:17,782 --> 00:40:19,783 You could think of it as a newborn baby coming into 787 00:40:19,884 --> 00:40:22,085 the world, kicking and screaming. 788 00:40:22,186 --> 00:40:23,553 ROWE: The turbulence produces 789 00:40:23,654 --> 00:40:26,456 a powerful blast of electromagnetic radiation. 790 00:40:28,859 --> 00:40:32,929 It races out of the collision site at the speed of light 791 00:40:33,030 --> 00:40:36,800 until we detect it as a fast radio burst. 792 00:40:38,502 --> 00:40:41,571 We can hear the screams of agony from millions 793 00:40:41,672 --> 00:40:42,772 of light-years away, 794 00:40:42,873 --> 00:40:46,910 and those screams are the fast radio bursts. 795 00:40:47,011 --> 00:40:48,912 This could be the most difficult childbirth in 796 00:40:49,013 --> 00:40:49,979 the cosmos. 797 00:40:55,286 --> 00:40:58,121 ROWE: Few suspected that white dwarfs could create 798 00:40:58,222 --> 00:41:00,590 something as violent as a magnetar. 799 00:41:03,561 --> 00:41:06,029 White dwarfs are emerging from out of 800 00:41:06,130 --> 00:41:08,965 the shadows and taking their rightful place 801 00:41:09,066 --> 00:41:11,801 as one of the most fascinating objects 802 00:41:11,902 --> 00:41:13,536 in the universe. 803 00:41:13,637 --> 00:41:16,206 When we first observed white dwarfs, they were weird. 804 00:41:16,307 --> 00:41:19,342 They were curious, but just like a sideshow. 805 00:41:19,443 --> 00:41:21,544 But now white dwarfs are showing us 806 00:41:21,645 --> 00:41:23,546 what they're truly capable of. 807 00:41:23,614 --> 00:41:25,348 STRAUGHN: White dwarfs can sort of be seen 808 00:41:25,449 --> 00:41:27,217 as these underdogs of the universe, 809 00:41:27,318 --> 00:41:30,353 but it's really become an exciting and cutting edge 810 00:41:30,454 --> 00:41:32,822 area of research. 811 00:41:32,923 --> 00:41:34,290 THALLER: Now we think these objects may have 812 00:41:34,391 --> 00:41:36,993 a lot of exciting science to deliver, things like, 813 00:41:37,094 --> 00:41:38,728 will the universe expand forever? 814 00:41:38,829 --> 00:41:40,563 What is the ultimate fate of the universe? 815 00:41:40,664 --> 00:41:44,801 All of that may be waiting for us inside a white dwarf. 816 00:41:44,902 --> 00:41:47,504 PLAIT: Discount these things at your own risk, 817 00:41:47,605 --> 00:41:48,805 because honestly, 818 00:41:48,906 --> 00:41:51,241 they are one of the driving forces in the universe. 819 00:41:51,342 --> 00:41:54,310 Just because it's little don't mean it ain't bad. 820 00:41:54,411 --> 00:41:56,246 Don't underestimate a white dwarf.