1 00:00:06,906 --> 00:00:08,374 Narrator: Supernovas -- 2 00:00:08,375 --> 00:00:13,512 gigantic explosions that light up the cosmos. 3 00:00:13,513 --> 00:00:15,748 One of the most spectacular things in the universe 4 00:00:15,749 --> 00:00:19,017 is the death of a giant star. 5 00:00:19,018 --> 00:00:22,788 They live fast, and they die young. 6 00:00:22,789 --> 00:00:24,990 Narrator: Inside the star's core, 7 00:00:24,991 --> 00:00:28,627 temperatures and pressures are immense. 8 00:00:28,628 --> 00:00:31,263 We're talking about a billion degrees 9 00:00:31,264 --> 00:00:33,866 in the center of one of these stars. 10 00:00:33,867 --> 00:00:35,367 Narrator: A ticking time bomb 11 00:00:35,368 --> 00:00:39,538 that explodes with indescribable energy. 12 00:00:39,539 --> 00:00:43,475 The last minutes of a giant star's life 13 00:00:43,476 --> 00:00:47,613 are the most cataclysmic events that we see in the universe. 14 00:00:47,614 --> 00:00:51,383 ♪♪ 15 00:00:51,384 --> 00:00:56,121 Narrator: Dramatic finales blazing across space. 16 00:00:56,122 --> 00:00:58,924 That one supernova is brighter 17 00:00:58,925 --> 00:01:00,959 than the hundreds of billions of stars 18 00:01:00,960 --> 00:01:02,594 that constitute the galaxy. 19 00:01:02,595 --> 00:01:04,229 How amazing is that? 20 00:01:04,230 --> 00:01:08,233 Narrator: But these stellar deaths also hold the key 21 00:01:08,234 --> 00:01:10,469 to life itself. 22 00:01:10,470 --> 00:01:14,339 Understanding supernovas is understanding our story. 23 00:01:14,340 --> 00:01:16,341 We owe our existence to them. 24 00:01:16,342 --> 00:01:19,344 Captions by vitac -- www.Vitac.Com 25 00:01:19,345 --> 00:01:22,382 captions paid for by discovery communications 26 00:01:25,585 --> 00:01:31,457 ♪♪ 27 00:01:31,458 --> 00:01:34,092 Narrator: Right now, somewhere in the universe, 28 00:01:34,093 --> 00:01:37,729 a giant star is detonating, 29 00:01:37,730 --> 00:01:40,833 creating a huge cosmic explosion 30 00:01:40,834 --> 00:01:43,202 called a supernova. 31 00:01:43,203 --> 00:01:48,073 ♪♪ 32 00:01:48,074 --> 00:01:54,947 Supernovas are a big, giant dramatic end to a star's life. 33 00:01:54,948 --> 00:01:58,450 ♪♪ 34 00:01:58,451 --> 00:02:00,686 Narrator: All stars die, 35 00:02:00,687 --> 00:02:04,456 but only the biggest go out with a bang. 36 00:02:04,457 --> 00:02:06,925 For a star to go supernova, we think it has to be 37 00:02:06,926 --> 00:02:10,529 at least eight times more massive than our sun. 38 00:02:10,530 --> 00:02:11,864 It's so easy to think of our sun 39 00:02:11,865 --> 00:02:14,967 as this incredibly gigantic thing, 40 00:02:14,968 --> 00:02:17,069 but our sun is absolutely tiny 41 00:02:17,070 --> 00:02:19,905 compared to some of the giant stars in the sky. 42 00:02:19,906 --> 00:02:25,677 ♪♪ 43 00:02:25,678 --> 00:02:29,848 Narrator: We can see some of these giant stars with the naked eye, 44 00:02:29,849 --> 00:02:32,484 and the 10th brightest in the night sky 45 00:02:32,485 --> 00:02:34,219 is a red supergiant 46 00:02:34,220 --> 00:02:38,924 around 15 times the mass of the sun -- 47 00:02:38,925 --> 00:02:40,893 betelgeuse. 48 00:02:40,894 --> 00:02:42,928 ♪♪ 49 00:02:42,929 --> 00:02:45,998 Betelgeuse is so big that if you were to place it 50 00:02:45,999 --> 00:02:47,699 in our own solar system, 51 00:02:47,700 --> 00:02:52,204 it would stretch to the orbit of Jupiter. 52 00:02:52,205 --> 00:02:54,806 This is one of the biggest beasts in the galaxy. 53 00:02:54,807 --> 00:02:58,277 It's a star also that is on the verge of death. 54 00:02:58,278 --> 00:03:00,312 ♪♪ 55 00:03:00,313 --> 00:03:04,917 Narrator: Betelgeuse is less than 10 million years old, 56 00:03:04,918 --> 00:03:07,853 but this huge star's days are numbered. 57 00:03:07,854 --> 00:03:09,888 It's ready to blow. 58 00:03:09,889 --> 00:03:13,058 ♪♪ 59 00:03:13,059 --> 00:03:15,861 When it does, we will see a region of sky 60 00:03:15,862 --> 00:03:18,163 brighten for 14 days, 61 00:03:18,164 --> 00:03:22,668 until it's nearly as bright as a full moon. 62 00:03:22,669 --> 00:03:24,803 It is going to be one of the most spectacular 63 00:03:24,804 --> 00:03:27,205 shows in history. 64 00:03:27,206 --> 00:03:29,274 ♪♪ 65 00:03:29,275 --> 00:03:30,609 And it could happen at any moment. 66 00:03:30,610 --> 00:03:31,944 I mean, this is the thing. 67 00:03:31,945 --> 00:03:34,646 I often stand outside in my yard in the wintertime. 68 00:03:34,647 --> 00:03:36,949 I look up at Orion, and I see betelgeuse. 69 00:03:36,950 --> 00:03:39,017 And I'm like, "explode!" 70 00:03:39,018 --> 00:03:40,953 ♪♪ 71 00:03:40,954 --> 00:03:44,623 Narrator: So what will make betelgeuse go supernova? 72 00:03:44,624 --> 00:03:47,225 To understand a giant star's death, 73 00:03:47,226 --> 00:03:50,095 we need to understand its life. 74 00:03:50,096 --> 00:03:52,698 ♪♪ 75 00:03:52,699 --> 00:03:55,801 From the day it's born until the day it dies, 76 00:03:55,802 --> 00:03:59,004 a star's life is a constant battle. 77 00:03:59,005 --> 00:04:00,872 ♪♪ 78 00:04:00,873 --> 00:04:02,941 Gravity is pulling in, 79 00:04:02,942 --> 00:04:06,378 and energy is pushing out. 80 00:04:06,379 --> 00:04:07,679 The interior of a star 81 00:04:07,680 --> 00:04:11,450 is fusing countless atomic nuclei together. 82 00:04:11,451 --> 00:04:13,118 Thaller: Atoms are ramming into each other, 83 00:04:13,119 --> 00:04:15,988 getting very, very close. 84 00:04:15,989 --> 00:04:17,222 And if they get close enough, 85 00:04:17,223 --> 00:04:20,726 they'll actually stick and form a larger atom. 86 00:04:20,727 --> 00:04:23,462 Narrator: Every second, a giant star fuses 87 00:04:23,463 --> 00:04:27,532 7 1/2 billion tons of hydrogen. 88 00:04:27,533 --> 00:04:29,434 That amount of energy is roughly equivalent 89 00:04:29,435 --> 00:04:34,172 to about 100 billion atomic bombs per second. 90 00:04:34,173 --> 00:04:35,941 That's a big-ass explosion. 91 00:04:35,942 --> 00:04:38,143 ♪♪ 92 00:04:38,144 --> 00:04:39,878 Narrator: This explosive energy 93 00:04:39,879 --> 00:04:43,682 threatens to blow the star apart, 94 00:04:43,683 --> 00:04:48,453 but the star's own massive gravity keeps the lid on. 95 00:04:48,454 --> 00:04:50,722 Straughn: Everything in the universe is a fight 96 00:04:50,723 --> 00:04:52,891 between the inward force of gravity 97 00:04:52,892 --> 00:04:56,294 and the outward force of pressure or energy. 98 00:04:56,295 --> 00:04:58,764 Thaller: Every single star in the sky, even our own sun, 99 00:04:58,765 --> 00:05:01,033 is an incredibly dynamic battleground. 100 00:05:01,034 --> 00:05:03,001 In many ways, stars are an explosion 101 00:05:03,002 --> 00:05:04,803 that are actually too big to explode. 102 00:05:04,804 --> 00:05:06,605 Gravity holds it together. 103 00:05:06,606 --> 00:05:09,141 ♪♪ 104 00:05:09,142 --> 00:05:12,077 Narrator: This battle between these two opposing forces 105 00:05:12,078 --> 00:05:15,881 determines the life and death of the star. 106 00:05:15,882 --> 00:05:18,617 And this is where size matters. 107 00:05:18,618 --> 00:05:22,788 The more massive the star, the more gravity pushes inward, 108 00:05:22,789 --> 00:05:27,993 the harder the star has to push outwards to keep itself alive. 109 00:05:27,994 --> 00:05:30,462 ♪♪ 110 00:05:30,463 --> 00:05:35,000 Very massive stars are like stars on steroids. 111 00:05:35,001 --> 00:05:37,569 They have a lot of fuel to burn. 112 00:05:37,570 --> 00:05:39,037 They're so powerful 113 00:05:39,038 --> 00:05:42,574 that they use up their fuel at a rapid rate. 114 00:05:42,575 --> 00:05:45,410 ♪♪ 115 00:05:45,411 --> 00:05:49,347 Narrator: Massive stars like betelgeuse are giant factories, 116 00:05:49,348 --> 00:05:52,517 fusing lighter elements into heavier ones. 117 00:05:52,518 --> 00:05:56,755 But the hard work doesn't start until their final years. 118 00:05:56,756 --> 00:06:02,327 For around 90% of their life, they fuse hydrogen into helium, 119 00:06:02,328 --> 00:06:07,332 but eventually, the hydrogen starts running out. 120 00:06:07,333 --> 00:06:09,501 In the core of a supergiant star, 121 00:06:09,502 --> 00:06:11,103 there's a sequence of fusion 122 00:06:11,104 --> 00:06:13,305 that goes from lighter elements to heavier elements, 123 00:06:13,306 --> 00:06:18,310 and it gets faster and faster every step of the way. 124 00:06:18,311 --> 00:06:21,213 Narrator: The countdown to death begins. 125 00:06:21,214 --> 00:06:23,915 The inward push from gravity takes over, 126 00:06:23,916 --> 00:06:27,052 raising the temperature in the core. 127 00:06:27,053 --> 00:06:30,388 Helium starts fusing to carbon. 128 00:06:30,389 --> 00:06:34,359 There's enough helium to last about a million years, 129 00:06:34,360 --> 00:06:36,294 but it too runs out, 130 00:06:36,295 --> 00:06:39,498 and things start speeding up. 131 00:06:39,499 --> 00:06:41,166 Plait: Carbon gets fused into neon. 132 00:06:41,167 --> 00:06:43,168 That takes about 1,000 years. 133 00:06:43,169 --> 00:06:44,736 Neon fusing into silicon? 134 00:06:44,737 --> 00:06:46,905 That takes about one year. 135 00:06:46,906 --> 00:06:49,174 Once it starts fusing silicon into iron, 136 00:06:49,175 --> 00:06:52,377 that takes one day. 137 00:06:52,378 --> 00:06:53,879 It gets more and more frantic. 138 00:06:53,880 --> 00:06:56,081 It's kind of like a cooking-contest show, 139 00:06:56,082 --> 00:06:57,315 where as the clock is running down, 140 00:06:57,316 --> 00:06:58,650 they're trying to do more and more things, 141 00:06:58,651 --> 00:07:00,152 and they get more and more frantic 142 00:07:00,153 --> 00:07:02,721 until, ding, time's up. 143 00:07:02,722 --> 00:07:05,824 ♪♪ 144 00:07:05,825 --> 00:07:09,861 Narrator: The star is now in its death throes. 145 00:07:09,862 --> 00:07:11,696 Sutter: Once iron production has started, 146 00:07:11,697 --> 00:07:13,431 the clock is ticking 147 00:07:13,432 --> 00:07:17,169 towards the cataclysmic end of this star. 148 00:07:17,170 --> 00:07:20,305 ♪♪ 149 00:07:20,306 --> 00:07:23,408 Narrator: A giant ball of incredibly dense iron forms 150 00:07:23,409 --> 00:07:27,479 in the middle of the dying star's core. 151 00:07:27,480 --> 00:07:31,616 This iron sphere is several thousand miles across 152 00:07:31,617 --> 00:07:34,719 and unbelievably hot. 153 00:07:34,720 --> 00:07:36,188 It gets so hot there 154 00:07:36,189 --> 00:07:37,923 that temperature almost becomes meaningless. 155 00:07:37,924 --> 00:07:40,659 I mean, we're talking about a billion degrees 156 00:07:40,660 --> 00:07:42,761 in the center of one of these stars. 157 00:07:42,762 --> 00:07:46,865 ♪♪ 158 00:07:46,866 --> 00:07:51,169 Narrator: This extreme heat is caused by fusion reactions. 159 00:07:51,170 --> 00:07:55,640 More and more reactions create heavier and heavier elements, 160 00:07:55,641 --> 00:07:59,311 and with each step, less and less energy is produced, 161 00:07:59,312 --> 00:08:01,880 until iron is created. 162 00:08:01,881 --> 00:08:04,649 Plait: When you try to fuse iron nuclei together, 163 00:08:04,650 --> 00:08:07,319 that takes energy. It doesn't generate energy. 164 00:08:07,320 --> 00:08:09,921 So once the core starts to fuse iron, 165 00:08:09,922 --> 00:08:13,692 it's basically stealing its own energy. 166 00:08:13,693 --> 00:08:15,093 Narrator: The growing iron core 167 00:08:15,094 --> 00:08:18,230 sucks more and more energy from the star. 168 00:08:18,231 --> 00:08:20,765 Gravity continues pulling in, 169 00:08:20,766 --> 00:08:24,903 overwhelming the outward pressure from inside the star. 170 00:08:24,904 --> 00:08:27,572 ♪♪ 171 00:08:27,573 --> 00:08:30,609 Everything gets crushed to unimaginable degrees. 172 00:08:30,610 --> 00:08:32,477 All of a sudden, there's no nuclear reaction 173 00:08:32,478 --> 00:08:35,280 to support the star against the crush of gravity. 174 00:08:35,281 --> 00:08:39,751 ♪♪ 175 00:08:39,752 --> 00:08:42,020 Narrator: With nothing left to hold it up, 176 00:08:42,021 --> 00:08:44,189 the star is doomed. 177 00:08:44,190 --> 00:08:46,091 Gravity wins. 178 00:08:46,092 --> 00:08:48,894 The edges of the iron core collapse. 179 00:08:48,895 --> 00:08:52,130 Trillions of tons of dense iron fall inward 180 00:08:52,131 --> 00:08:54,599 at 1/4 the speed of light. 181 00:08:54,600 --> 00:08:59,070 The star now has less than one second left to live. 182 00:08:59,071 --> 00:09:03,408 Things start to fall apart real quickly. 183 00:09:03,409 --> 00:09:05,343 The core collapse is so fast 184 00:09:05,344 --> 00:09:06,778 that the outer layers of the star 185 00:09:06,779 --> 00:09:09,247 don't even have time to react. They're just hanging there. 186 00:09:09,248 --> 00:09:10,582 It's kind of like wile e. Coyote, 187 00:09:10,583 --> 00:09:12,217 when a cliff collapses underneath him, 188 00:09:12,218 --> 00:09:14,819 and he doesn't even fall until he notices. 189 00:09:14,820 --> 00:09:16,855 ♪♪ 190 00:09:16,856 --> 00:09:19,524 Narrator: The rest of the star collapses. 191 00:09:19,525 --> 00:09:24,429 A trillion-trillion-trillion tons of gas hurtles inwards, 192 00:09:24,430 --> 00:09:26,197 following the iron. 193 00:09:26,198 --> 00:09:28,600 Thaller: Think about the entire mass of a star 194 00:09:28,601 --> 00:09:31,569 that has been held up by nuclear reactions inside. 195 00:09:31,570 --> 00:09:33,104 All of a sudden, those nuclear reactions 196 00:09:33,105 --> 00:09:35,106 go away in a split second. 197 00:09:35,107 --> 00:09:39,044 Everything rushes into the middle. 198 00:09:39,045 --> 00:09:41,112 And that sets off the most dramatic explosion 199 00:09:41,113 --> 00:09:42,547 in the universe. 200 00:09:42,548 --> 00:09:50,422 ♪♪ 201 00:09:50,423 --> 00:09:52,190 Narrator: The spectacular death blow 202 00:09:52,191 --> 00:09:55,660 can outshine all of the stars in a galaxy. 203 00:09:55,661 --> 00:09:58,496 ♪♪ 204 00:09:58,497 --> 00:10:00,198 But there's a problem. 205 00:10:00,199 --> 00:10:02,400 We still don't fully understand 206 00:10:02,401 --> 00:10:06,438 how a collapsing ball of iron and tons of falling gas 207 00:10:06,439 --> 00:10:10,008 create a giant fireball. 208 00:10:10,009 --> 00:10:13,812 How this collapsing core triggers a massive explosion 209 00:10:13,813 --> 00:10:16,716 is one of the biggest mysteries in astrophysics. 210 00:10:29,528 --> 00:10:38,303 ♪♪ 211 00:10:38,304 --> 00:10:39,871 Narrator: A supernova -- 212 00:10:39,872 --> 00:10:43,074 one of the most powerful eruptions in the cosmos, 213 00:10:43,075 --> 00:10:46,811 triggered by the collapse of a massive star. 214 00:10:46,812 --> 00:10:49,581 How do you go from a violent collapse 215 00:10:49,582 --> 00:10:52,050 to an incredibly dramatic explosion? 216 00:10:52,051 --> 00:10:55,720 This involves some of the most complex astrophysics 217 00:10:55,721 --> 00:10:59,357 known to humanity, and we don't fully understand 218 00:10:59,358 --> 00:11:02,127 the details of the process. 219 00:11:02,128 --> 00:11:03,561 Narrator: We're missing something, 220 00:11:03,562 --> 00:11:07,432 because we nearly always spot supernovas too late. 221 00:11:07,433 --> 00:11:09,534 What you're seeing is, you're seeing the star brightening, 222 00:11:09,535 --> 00:11:12,003 and that's really happening after the fact. 223 00:11:12,004 --> 00:11:16,174 So now the magic key is not finding a supernova 224 00:11:16,175 --> 00:11:19,344 but finding the moment that we call the breakout. 225 00:11:19,345 --> 00:11:24,549 ♪♪ 226 00:11:24,550 --> 00:11:28,053 Narrator: The breakout is a giant star's death rattle. 227 00:11:28,054 --> 00:11:30,722 It's the moment after the core has collapsed, 228 00:11:30,723 --> 00:11:35,860 when the star blows apart in a huge flash of visible light. 229 00:11:35,861 --> 00:11:38,430 ♪♪ 230 00:11:38,431 --> 00:11:40,865 But in the entire history of astronomy, 231 00:11:40,866 --> 00:11:44,035 this moment has only been caught twice -- 232 00:11:44,036 --> 00:11:46,438 one by NASA's multimillion-dollar 233 00:11:46,439 --> 00:11:48,606 space telescope, kepler, 234 00:11:48,607 --> 00:11:53,912 and once by a very lucky Argentinean amateur. 235 00:11:53,913 --> 00:11:55,180 Plait: I love this story. 236 00:11:55,181 --> 00:11:57,048 There's an amateur astronomer named Victor buso. 237 00:11:57,049 --> 00:12:00,785 He has a very nice telescope in an observatory in his yard. 238 00:12:00,786 --> 00:12:02,987 And he was taking photographs repeatedly 239 00:12:02,988 --> 00:12:06,157 of the same galaxy that happened to be overhead. 240 00:12:06,158 --> 00:12:07,559 Oluseyi: And he just happened to be looking 241 00:12:07,560 --> 00:12:09,194 at the right region of the sky, 242 00:12:09,195 --> 00:12:13,331 and he luckily caught the shock breakout of a supernova. 243 00:12:13,332 --> 00:12:15,867 ♪♪ 244 00:12:15,868 --> 00:12:18,336 Narrator: The chances of catching this moment 245 00:12:18,337 --> 00:12:21,506 are 1 in 10 million. 246 00:12:21,507 --> 00:12:23,475 What Victor caught was the moment 247 00:12:23,476 --> 00:12:25,577 the shock wave reaches the surface. 248 00:12:25,578 --> 00:12:27,512 ♪♪ 249 00:12:27,513 --> 00:12:29,280 Narrator: Victor noticed this spot 250 00:12:29,281 --> 00:12:31,516 appearing in his photographs. 251 00:12:31,517 --> 00:12:34,385 Realizing he'd captured the first flash of light 252 00:12:34,386 --> 00:12:36,254 from an exploding star, 253 00:12:36,255 --> 00:12:40,258 he alerted professional astronomers across the globe. 254 00:12:40,259 --> 00:12:42,193 ♪♪ 255 00:12:42,194 --> 00:12:46,264 When I heard of his discovery, I was like, "no way. 256 00:12:46,265 --> 00:12:50,168 How could this guy, using a camera on his telescope 257 00:12:50,169 --> 00:12:51,870 for the very first time, 258 00:12:51,871 --> 00:12:55,707 pointing at a single random galaxy in the sky, 259 00:12:55,708 --> 00:12:58,309 have found this exploding star 260 00:12:58,310 --> 00:13:00,445 in the first hour of its explosion? 261 00:13:00,446 --> 00:13:03,882 It's almost too good to be true." 262 00:13:03,883 --> 00:13:05,783 Narrator: Alex filippenko and his team 263 00:13:05,784 --> 00:13:09,521 monitored the brightening light from the star. 264 00:13:09,522 --> 00:13:13,591 Filippenko: What we found when studying the light from buso's supernova 265 00:13:13,592 --> 00:13:18,830 is that the object brightened very quickly for a short time 266 00:13:18,831 --> 00:13:22,100 when a shock wave, a supersonic wave 267 00:13:22,101 --> 00:13:27,071 going through the star burst out through the surface. 268 00:13:27,072 --> 00:13:28,806 And when it gets right to the edge, 269 00:13:28,807 --> 00:13:32,710 that huge amount of energy is released as a tremendous flash. 270 00:13:32,711 --> 00:13:35,280 That is the moment of shock breakout. 271 00:13:35,281 --> 00:13:38,082 ♪♪ 272 00:13:38,083 --> 00:13:40,318 Narrator: The monstrous shock wave travels 273 00:13:40,319 --> 00:13:43,421 at nearly 30,000 miles per hour, 274 00:13:43,422 --> 00:13:45,990 bursting through the surface of the star 275 00:13:45,991 --> 00:13:47,292 and ripping it to pieces. 276 00:13:47,293 --> 00:13:48,793 Fire! 277 00:13:48,794 --> 00:13:53,965 ♪♪ 278 00:13:53,966 --> 00:13:58,036 Narrator: We see shock waves from explosions on earth. 279 00:13:58,037 --> 00:14:01,839 They can travel through gas, liquid, and solid, 280 00:14:01,840 --> 00:14:05,410 including the layers of a collapsing star. 281 00:14:05,411 --> 00:14:07,946 ♪♪ 282 00:14:07,947 --> 00:14:09,614 Thaller: This observation of the shock wave 283 00:14:09,615 --> 00:14:12,450 reaching the surface of the star was incredibly important, 284 00:14:12,451 --> 00:14:14,652 because Victor managed to catch a star 285 00:14:14,653 --> 00:14:16,754 the moment is actually went supernova. 286 00:14:16,755 --> 00:14:21,292 That is something that is a scientific treasure. 287 00:14:21,293 --> 00:14:25,430 Narrator: The shock breakout is like cosmic gold dust, 288 00:14:25,431 --> 00:14:29,767 a flash in the pan that lasts 20 minutes -- 289 00:14:29,768 --> 00:14:33,137 just the blink of an eye on astronomical time scales. 290 00:14:33,138 --> 00:14:35,073 ♪♪ 291 00:14:35,074 --> 00:14:37,709 But what sets the shock wave off? 292 00:14:37,710 --> 00:14:40,845 Is it just a question of bounce? 293 00:14:40,846 --> 00:14:43,414 A supernova shock wave can be explained 294 00:14:43,415 --> 00:14:46,084 with the help of a basketball. 295 00:14:46,085 --> 00:14:48,019 The thing about an exploding star 296 00:14:48,020 --> 00:14:50,622 is that the nuclear reactions go out in the core, 297 00:14:50,623 --> 00:14:52,824 and then the outer layers fall in 298 00:14:52,825 --> 00:14:55,994 at incredibly high speeds toward the inner core, 299 00:14:55,995 --> 00:14:58,963 and then it rebounds and bounces out. 300 00:14:58,964 --> 00:15:02,634 And what gives it so much energy is the structure of the star. 301 00:15:02,635 --> 00:15:04,602 ♪♪ 302 00:15:04,603 --> 00:15:07,405 Narrator: As the dying star burns through its fuel, 303 00:15:07,406 --> 00:15:10,508 it creates layers of different elements -- 304 00:15:10,509 --> 00:15:12,110 heavy iron at the core, 305 00:15:12,111 --> 00:15:15,880 with layers and layers of lighter elements above. 306 00:15:15,881 --> 00:15:17,715 So, let's say there was only one layer, 307 00:15:17,716 --> 00:15:20,551 and there was a rebound, like dropping this ball. 308 00:15:20,552 --> 00:15:22,220 It doesn't bounce very high. 309 00:15:22,221 --> 00:15:24,455 But let's say it's organized like a star, 310 00:15:24,456 --> 00:15:26,190 where the heavy thing is at the bottom, 311 00:15:26,191 --> 00:15:27,792 the lighter thing is at the top. 312 00:15:27,793 --> 00:15:30,361 And let's see how this rebound goes. 313 00:15:30,362 --> 00:15:36,968 ♪♪ 314 00:15:36,969 --> 00:15:40,338 Now, that was a rebound. 315 00:15:40,339 --> 00:15:42,807 Narrator: The tennis ball launches off the basketball 316 00:15:42,808 --> 00:15:45,209 because energy from the basketball's bounce 317 00:15:45,210 --> 00:15:47,779 is transferred upwards. 318 00:15:47,780 --> 00:15:50,648 The same thing happens in a collapsing star, 319 00:15:50,649 --> 00:15:53,318 but with many more layers. 320 00:15:53,319 --> 00:15:56,654 All the different elements collapse inwards. 321 00:15:56,655 --> 00:15:59,424 They heavier layers hit the dense core first, 322 00:15:59,425 --> 00:16:02,226 passing energy to the lighter ones. 323 00:16:02,227 --> 00:16:06,097 And this creates the shock wave. 324 00:16:06,098 --> 00:16:09,567 But this energy isn't enough to propel the shock wave 325 00:16:09,568 --> 00:16:12,737 all the way out of the star. 326 00:16:12,738 --> 00:16:15,139 The problem is, when we looked at this in detail 327 00:16:15,140 --> 00:16:17,742 using computer models, it didn't work. 328 00:16:17,743 --> 00:16:19,377 The shock wave seemed to stall. 329 00:16:19,378 --> 00:16:21,379 We couldn't get the star to explode. 330 00:16:21,380 --> 00:16:25,249 For 50 years, we couldn't figure out what we were missing. 331 00:16:25,250 --> 00:16:28,353 Narrator: Scientists suspect something else is involved, 332 00:16:28,354 --> 00:16:32,290 something that's almost impossible to detect. 333 00:16:32,291 --> 00:16:36,595 Could there be a ghost in the supernova machine? 334 00:16:48,340 --> 00:16:53,244 ♪♪ 335 00:16:53,245 --> 00:16:56,347 Narrator: When stars as big as betelgeuse die, 336 00:16:56,348 --> 00:16:59,117 their explosive deaths send shock waves 337 00:16:59,118 --> 00:17:02,587 that travel trillions of miles through space. 338 00:17:02,588 --> 00:17:04,789 But how these shock waves are created 339 00:17:04,790 --> 00:17:08,326 has puzzled scientists for decades. 340 00:17:08,327 --> 00:17:09,827 Time and time again, 341 00:17:09,828 --> 00:17:12,230 when we actually went back to our computers and our theories 342 00:17:12,231 --> 00:17:15,199 and looked at how supernovas should work, they just didn't. 343 00:17:15,200 --> 00:17:18,803 They shouldn't actually explode. 344 00:17:18,804 --> 00:17:20,271 Narrator: In computer models, 345 00:17:20,272 --> 00:17:23,474 the bounce from falling gas on a collapsing core 346 00:17:23,475 --> 00:17:27,211 can't drive the shock wave all the way out of the star. 347 00:17:27,212 --> 00:17:30,415 Something crucial is missing. 348 00:17:30,416 --> 00:17:32,984 What we needed from inside the core of the star 349 00:17:32,985 --> 00:17:35,153 was a completely new source of energy, 350 00:17:35,154 --> 00:17:37,655 something to actually make that final push 351 00:17:37,656 --> 00:17:40,925 to get the star to rip itself apart. 352 00:17:40,926 --> 00:17:42,627 Narrator: Scientists suspect this energy 353 00:17:42,628 --> 00:17:48,299 comes from an enigmatic particle called a neutrino. 354 00:17:48,300 --> 00:17:51,035 Neutrinos are a type of fundamental physical particle 355 00:17:51,036 --> 00:17:54,405 that are still a little bit mysterious to us. 356 00:17:54,406 --> 00:17:55,773 They're almost like ghost particles. 357 00:17:55,774 --> 00:17:58,409 They travel through us without touching us at all. 358 00:17:58,410 --> 00:18:02,013 ♪♪ 359 00:18:02,014 --> 00:18:05,149 Narrator: Like particles of light, photons, 360 00:18:05,150 --> 00:18:08,653 neutrinos carry no electrical charge. 361 00:18:08,654 --> 00:18:12,824 But unlike photons, they can pass through stars, 362 00:18:12,825 --> 00:18:15,126 planets, and us. 363 00:18:15,127 --> 00:18:17,328 So where do they come from? 364 00:18:17,329 --> 00:18:19,597 Scientists predict the source 365 00:18:19,598 --> 00:18:22,867 is the star itself. 366 00:18:22,868 --> 00:18:24,635 In the middle of the core of the star, 367 00:18:24,636 --> 00:18:27,371 you're producing something called a neutron star -- 368 00:18:27,372 --> 00:18:30,007 an amazing, super-compressed ball of matter 369 00:18:30,008 --> 00:18:32,910 only about 10 miles across. 370 00:18:32,911 --> 00:18:35,813 Narrator: As the iron core of a star collapses, 371 00:18:35,814 --> 00:18:38,950 the atoms are crushed together. 372 00:18:38,951 --> 00:18:43,888 Protons and electrons are forced to combine to form neutrons. 373 00:18:43,889 --> 00:18:48,359 This process releases vast quantities of neutrinos. 374 00:18:48,360 --> 00:18:50,995 ♪♪ 375 00:18:50,996 --> 00:18:53,898 Despite being one of the most abundant particles 376 00:18:53,899 --> 00:18:55,333 in the universe, 377 00:18:55,334 --> 00:18:59,036 neutrinos are notoriously difficult to detect. 378 00:18:59,037 --> 00:19:03,641 ♪♪ 379 00:19:03,642 --> 00:19:08,312 But in 1987, scientists got lucky. 380 00:19:08,313 --> 00:19:12,851 A massive star went supernova in a nearby galaxy. 381 00:19:15,521 --> 00:19:19,390 In 1987, astronomers got a wonderful gift. 382 00:19:19,391 --> 00:19:22,927 It was the first naked-eye supernova 383 00:19:22,928 --> 00:19:25,162 in about 400 years. 384 00:19:25,163 --> 00:19:28,165 And we had lots and lots of telescopes 385 00:19:28,166 --> 00:19:29,667 with which to study it 386 00:19:29,668 --> 00:19:32,703 throughout the electromagnetic spectrum. 387 00:19:32,704 --> 00:19:34,939 ♪♪ 388 00:19:34,940 --> 00:19:37,642 Narrator: But the 1987a supernova 389 00:19:37,643 --> 00:19:42,246 set off another scientific instrument -- 390 00:19:42,247 --> 00:19:47,752 a neutrino detector hidden deep below a mountain in Japan. 391 00:19:47,753 --> 00:19:50,988 There was a burst of neutrinos associated with the supernova. 392 00:19:50,989 --> 00:19:53,925 This was just a fantastic surprise, 393 00:19:53,926 --> 00:19:56,460 a wonderful added bonus. 394 00:19:56,461 --> 00:20:00,398 When you're trying to capture and measure elusive particles 395 00:20:00,399 --> 00:20:01,566 that you don't even know 396 00:20:01,567 --> 00:20:02,867 if you're gonna get a signal or not, 397 00:20:02,868 --> 00:20:05,169 and you're sitting there waiting at your detector, 398 00:20:05,170 --> 00:20:07,405 and then suddenly, this thing just lights up? 399 00:20:07,406 --> 00:20:10,841 How exciting is that? 400 00:20:10,842 --> 00:20:12,877 Narrator: This was definitive proof 401 00:20:12,878 --> 00:20:17,248 that supernovas emit neutrinos. 402 00:20:17,249 --> 00:20:20,952 Neutrinos may be ghostly, but they don't gently drift out 403 00:20:20,953 --> 00:20:23,387 from the collapsing core of the star. 404 00:20:23,388 --> 00:20:26,324 They have to burst out. 405 00:20:26,325 --> 00:20:29,460 The amazing thing about the inside of a supernova explosion 406 00:20:29,461 --> 00:20:33,431 is that it's getting dense enough to trap neutrinos. 407 00:20:33,432 --> 00:20:35,700 All of a sudden now, there's pressure. 408 00:20:35,701 --> 00:20:38,269 ♪♪ 409 00:20:38,270 --> 00:20:40,471 Narrator: When scientists add neutrino pressure 410 00:20:40,472 --> 00:20:42,139 to the computer models, 411 00:20:42,140 --> 00:20:45,509 the shock wave gets farther away from the core, 412 00:20:45,510 --> 00:20:48,746 but the supernova still doesn't explode. 413 00:20:48,747 --> 00:20:53,584 One more ingredient is needed -- disorder. 414 00:20:53,585 --> 00:20:57,588 Because stars are round, it's tempting to think 415 00:20:57,589 --> 00:21:02,393 that a supernova explosion too will be round. 416 00:21:02,394 --> 00:21:07,231 But supernova aren't perfectly symmetric. 417 00:21:07,232 --> 00:21:08,733 Narrator: Energy from the shock wave 418 00:21:08,734 --> 00:21:11,102 and the neutrinos heats up the gas 419 00:21:11,103 --> 00:21:14,839 in chaotic, unpredictable ways. 420 00:21:14,840 --> 00:21:18,576 They cause hot bubbles to rise and then come back down 421 00:21:18,577 --> 00:21:19,810 and rise and come back down. 422 00:21:19,811 --> 00:21:22,013 It's sort of a boiling motion. 423 00:21:22,014 --> 00:21:25,449 This imparts a lot of turbulence into the gas. 424 00:21:25,450 --> 00:21:27,752 Narrator: Researchers add all the ingredients 425 00:21:27,753 --> 00:21:30,821 to a supercomputer and let it run. 426 00:21:30,822 --> 00:21:32,923 ♪♪ 427 00:21:32,924 --> 00:21:36,761 This simulation is the result. 428 00:21:36,762 --> 00:21:40,231 When the shock wave stalls on its way out of the core, 429 00:21:40,232 --> 00:21:44,535 it creates tiny ripples in the falling elements above. 430 00:21:44,536 --> 00:21:48,439 The ripples become giant sloshing waves. 431 00:21:48,440 --> 00:21:51,676 Neutrinos bursting out from the neutron star 432 00:21:51,677 --> 00:21:54,011 heat the layers of elements above it, 433 00:21:54,012 --> 00:21:57,181 causing them to bubble and rise. 434 00:21:57,182 --> 00:21:59,917 ♪♪ 435 00:21:59,918 --> 00:22:02,486 Eventually, the intense heat combines 436 00:22:02,487 --> 00:22:05,389 with the pressures of these violent motions, 437 00:22:05,390 --> 00:22:09,360 driving the shock wave out like an interstellar Tsunami, 438 00:22:09,361 --> 00:22:12,296 smashing the star to pieces. 439 00:22:12,297 --> 00:22:21,772 ♪♪ 440 00:22:21,773 --> 00:22:23,874 It turns out, stars do explode. 441 00:22:23,875 --> 00:22:25,576 Nature knows what it's doing. 442 00:22:25,577 --> 00:22:28,212 It was the computer models. They were too simple. 443 00:22:28,213 --> 00:22:30,381 Once the models became more complex, 444 00:22:30,382 --> 00:22:33,451 starting taking into account all the dimensions of a star, 445 00:22:33,452 --> 00:22:36,087 the supernova models started to explode. 446 00:22:36,088 --> 00:22:38,789 We think of supernova as effectively simple events -- 447 00:22:38,790 --> 00:22:41,525 very violent events, but simple. 448 00:22:41,526 --> 00:22:43,928 And this is just a beautiful illustration of the fact 449 00:22:43,929 --> 00:22:45,963 that when you dig deep down, 450 00:22:45,964 --> 00:22:48,165 these are really exquisitely complex 451 00:22:48,166 --> 00:22:52,203 and elegant fluid-dynamics problems. 452 00:22:52,204 --> 00:22:53,704 Narrator: The shock wave travels through 453 00:22:53,705 --> 00:22:58,008 all the layers of the elements that make up the massive star. 454 00:22:58,009 --> 00:23:00,911 It takes hours for it to reach the outer edge 455 00:23:00,912 --> 00:23:03,681 and trigger the first flash of light, 456 00:23:03,682 --> 00:23:07,952 but this flash is just the start of the supernova. 457 00:23:07,953 --> 00:23:11,756 The spectacular light show is just beginning, 458 00:23:11,757 --> 00:23:16,762 a light show that will create elements essential for life. 459 00:23:28,673 --> 00:23:34,745 ♪♪ 460 00:23:34,746 --> 00:23:40,785 ♪♪ 461 00:23:40,786 --> 00:23:43,120 Narrator: We see the light from supernovas 462 00:23:43,121 --> 00:23:46,557 all the way across the cosmos, 463 00:23:46,558 --> 00:23:50,961 but what we're seeing isn't the explosive first flash. 464 00:23:50,962 --> 00:23:56,700 That's just the opening act before the main event. 465 00:23:56,701 --> 00:23:59,003 Supernova are some of the most energetic events 466 00:23:59,004 --> 00:24:01,972 in the universe. 467 00:24:01,973 --> 00:24:04,708 The galaxy has hundreds of billions of stars in it, 468 00:24:04,709 --> 00:24:06,443 and yet the death of this one star 469 00:24:06,444 --> 00:24:09,647 can outshine those hundred billions of stars. 470 00:24:09,648 --> 00:24:11,682 One of the interesting things about supernovas 471 00:24:11,683 --> 00:24:14,285 is that when the star explodes, 472 00:24:14,286 --> 00:24:17,254 it's not at its maximum brightness immediately. 473 00:24:17,255 --> 00:24:19,523 It takes days and weeks. 474 00:24:19,524 --> 00:24:25,396 ♪♪ 475 00:24:25,397 --> 00:24:29,867 Narrator: The first flash is the explosive part of a supernova, 476 00:24:29,868 --> 00:24:34,672 blasting tons of matter into space around the dying star. 477 00:24:34,673 --> 00:24:39,577 But it's this ejected debris that makes supernovas shine, 478 00:24:39,578 --> 00:24:43,848 often glowing brighter than the explosion itself. 479 00:24:43,849 --> 00:24:46,784 ♪♪ 480 00:24:46,785 --> 00:24:50,688 Heavy elements are formed inside the cores of massive stars, 481 00:24:50,689 --> 00:24:53,924 and even heavier elements are formed 482 00:24:53,925 --> 00:24:57,361 during the explosion event itself. 483 00:24:57,362 --> 00:25:00,231 ♪♪ 484 00:25:00,232 --> 00:25:02,032 Narrator: As the star rips apart, 485 00:25:02,033 --> 00:25:04,935 temperatures and pressures are immense. 486 00:25:04,936 --> 00:25:08,205 The elements that once made up the layers of the star 487 00:25:08,206 --> 00:25:11,575 fuse together, creating heavier elements. 488 00:25:11,576 --> 00:25:15,145 And some of these are radioactive. 489 00:25:15,146 --> 00:25:17,615 The decay of these radioactive elements 490 00:25:17,616 --> 00:25:19,116 actually produces light. 491 00:25:19,117 --> 00:25:22,386 That gives it more brightness over a longer period of time 492 00:25:22,387 --> 00:25:24,288 than it otherwise would have. 493 00:25:24,289 --> 00:25:26,891 ♪♪ 494 00:25:26,892 --> 00:25:29,426 Narrator: This cloud of brightly shining matter 495 00:25:29,427 --> 00:25:33,330 can last for months and sometimes years. 496 00:25:33,331 --> 00:25:35,733 ♪♪ 497 00:25:35,734 --> 00:25:38,869 These supernova remnants light up the universe 498 00:25:38,870 --> 00:25:41,505 like cosmic fireworks. 499 00:25:41,506 --> 00:25:43,440 ♪♪ 500 00:25:43,441 --> 00:25:45,776 These are oftentimes beautiful, 501 00:25:45,777 --> 00:25:47,778 beautiful things in the night sky, 502 00:25:47,779 --> 00:25:49,647 because they are -- you see remnants 503 00:25:49,648 --> 00:25:53,684 of everything that the supernova has generated in its explosion. 504 00:25:53,685 --> 00:25:56,220 ♪♪ 505 00:25:56,221 --> 00:25:59,823 Narrator: But these aren't just pretty light show. 506 00:25:59,824 --> 00:26:02,660 They are crucial for the evolution of galaxies 507 00:26:02,661 --> 00:26:05,796 and solar systems. 508 00:26:05,797 --> 00:26:08,098 Sutter: Necessary ingredients -- 509 00:26:08,099 --> 00:26:11,368 things like sulfur, things like phosphorous, 510 00:26:11,369 --> 00:26:14,438 things like carbon and oxygen. 511 00:26:14,439 --> 00:26:18,375 And even the elements necessary to build a rocky planet 512 00:26:18,376 --> 00:26:20,010 like the earth itself 513 00:26:20,011 --> 00:26:22,513 can only be formed inside of massive stars 514 00:26:22,514 --> 00:26:26,750 and can only be spread through supernova explosions. 515 00:26:26,751 --> 00:26:32,222 ♪♪ 516 00:26:32,223 --> 00:26:34,858 Narrator: NASA's chandra space telescope studies 517 00:26:34,859 --> 00:26:38,395 one of the most famous objects in the milky way... 518 00:26:38,396 --> 00:26:41,699 ♪♪ 519 00:26:41,700 --> 00:26:45,569 ...supernova remnant cassiopeia "a." 520 00:26:45,570 --> 00:26:47,771 ♪♪ 521 00:26:47,772 --> 00:26:51,608 Cassiopeia "a" is a relatively young supernova remnant, 522 00:26:51,609 --> 00:26:54,411 not even 400 years old. 523 00:26:54,412 --> 00:26:56,513 Narrator: Ever since its star exploded, 524 00:26:56,514 --> 00:26:59,583 cassiopeia "a" has been expanding. 525 00:26:59,584 --> 00:27:03,253 It is now 29 light years across. 526 00:27:03,254 --> 00:27:06,123 Using x-rays, the chandra space telescope 527 00:27:06,124 --> 00:27:10,294 has looked inside this massive cloud. 528 00:27:10,295 --> 00:27:13,197 New observations of cassiopeia "a" have shown us 529 00:27:13,198 --> 00:27:15,532 that the ejecta from this event 530 00:27:15,533 --> 00:27:18,869 has created tens of thousands of times 531 00:27:18,870 --> 00:27:24,174 the earth mass of really important materials. 532 00:27:24,175 --> 00:27:28,846 Filippenko: 70,000 earth masses worth of iron, 533 00:27:28,847 --> 00:27:33,150 and a whopping 1 million earth masses worth of oxygen. 534 00:27:33,151 --> 00:27:35,886 Now, these are elements that are important to life, 535 00:27:35,887 --> 00:27:37,855 to earth, to us. 536 00:27:37,856 --> 00:27:40,924 The iron in your blood, the calcium in your bones, 537 00:27:40,925 --> 00:27:44,461 these were forged in supernova explosions 538 00:27:44,462 --> 00:27:47,564 billions of years ago. 539 00:27:47,565 --> 00:27:49,400 Narrator: The new study reveals 540 00:27:49,401 --> 00:27:54,004 something even more extraordinary. 541 00:27:54,005 --> 00:27:56,740 Cassiopeia "a" also holds 542 00:27:56,741 --> 00:27:59,610 the building blocks of life. 543 00:27:59,611 --> 00:28:02,446 We see every single atom necessary for DNA 544 00:28:02,447 --> 00:28:04,982 in that one supernova remnant. 545 00:28:04,983 --> 00:28:07,651 One of the really cool things about supernovas 546 00:28:07,652 --> 00:28:11,488 is that our very existence depends on them. 547 00:28:11,489 --> 00:28:15,225 Our DNA molecules are made up of material 548 00:28:15,226 --> 00:28:18,062 that was once in the core of a massive star. 549 00:28:18,063 --> 00:28:19,329 So somewhere out there, 550 00:28:19,330 --> 00:28:21,865 some unnamed supernova eons ago, 551 00:28:21,866 --> 00:28:26,236 led to you watching me talking about supernovas. 552 00:28:26,237 --> 00:28:27,738 That's awesome. 553 00:28:27,739 --> 00:28:30,407 ♪♪ 554 00:28:30,408 --> 00:28:33,210 Narrator: Supernovas create all the elements needed 555 00:28:33,211 --> 00:28:37,081 to build everything from planets to humans. 556 00:28:37,082 --> 00:28:40,117 Dying stars give us life. 557 00:28:40,118 --> 00:28:43,921 It's a cosmic recycling process. 558 00:28:43,922 --> 00:28:49,761 But what if some stars are faking their own deaths? 559 00:29:02,140 --> 00:29:05,843 ♪♪ 560 00:29:05,844 --> 00:29:07,478 Narrator: For thousands of years, 561 00:29:07,479 --> 00:29:10,280 humans have wondered about bright, new stars 562 00:29:10,281 --> 00:29:12,316 appearing in the sky, 563 00:29:12,317 --> 00:29:16,620 and supernovas continue to surprise us. 564 00:29:16,621 --> 00:29:19,289 Our fascination with supernova has grown 565 00:29:19,290 --> 00:29:22,860 with each discovery of a new event. 566 00:29:22,861 --> 00:29:24,461 The study of supernovas 567 00:29:24,462 --> 00:29:26,830 is really going through a revolution. 568 00:29:26,831 --> 00:29:28,699 We're learning more and more. 569 00:29:28,700 --> 00:29:33,570 We're better able to find them and observe them. 570 00:29:33,571 --> 00:29:37,674 Narrator: And it turns out not all supernovas are the same. 571 00:29:37,675 --> 00:29:40,344 Some are the result of white dwarf stars 572 00:29:40,345 --> 00:29:42,179 stealing matter from a twin 573 00:29:42,180 --> 00:29:45,015 and growing so big, they explode. 574 00:29:45,016 --> 00:29:52,623 ♪♪ 575 00:29:52,624 --> 00:29:55,392 All other supernovas are massive stars 576 00:29:55,393 --> 00:29:58,562 collapsing under their own gravity. 577 00:29:58,563 --> 00:30:01,899 ♪♪ 578 00:30:01,900 --> 00:30:04,535 But just to confuse things further, 579 00:30:04,536 --> 00:30:07,471 scientists also categorize supernovas 580 00:30:07,472 --> 00:30:10,407 based on whether hydrogen is present. 581 00:30:10,408 --> 00:30:13,076 Type I are missing hydrogen. 582 00:30:13,077 --> 00:30:15,512 Type ii are not. 583 00:30:15,513 --> 00:30:18,482 So, astronomers have these categories for supernova, 584 00:30:18,483 --> 00:30:19,750 and that might make you think 585 00:30:19,751 --> 00:30:21,785 that we've got them all figured out, 586 00:30:21,786 --> 00:30:24,388 but here's a spoiler -- we don't. 587 00:30:24,389 --> 00:30:28,392 ♪♪ 588 00:30:28,393 --> 00:30:31,061 Narrator: September 2014. 589 00:30:31,062 --> 00:30:34,331 A supernova appears in the great bear constellation 590 00:30:34,332 --> 00:30:38,202 and glows brightly for 600 days. 591 00:30:38,203 --> 00:30:40,804 When scientists check the records, 592 00:30:40,805 --> 00:30:42,906 they discover a supernova was sighted 593 00:30:42,907 --> 00:30:46,977 at the exact same spot 60 years before. 594 00:30:46,978 --> 00:30:49,413 A star seemed to be dying 595 00:30:49,414 --> 00:30:53,383 over and over again. 596 00:30:53,384 --> 00:30:55,018 This particular star was something 597 00:30:55,019 --> 00:30:56,453 we had never seen before, 598 00:30:56,454 --> 00:30:59,923 and it seemed so strange, it was almost impossible. 599 00:30:59,924 --> 00:31:03,093 It actually brightened and faded about five times 600 00:31:03,094 --> 00:31:05,929 over a several-year time span. 601 00:31:05,930 --> 00:31:09,399 And each of these brightenings would have qualified 602 00:31:09,400 --> 00:31:12,970 as a supernova in terms of its total energy. 603 00:31:12,971 --> 00:31:17,007 It's the supernova that would never die. 604 00:31:17,008 --> 00:31:20,310 Thaller: So how could it happen with the same star again 605 00:31:20,311 --> 00:31:22,012 and again and again? 606 00:31:22,013 --> 00:31:26,216 This really did seem to be a zombie star. 607 00:31:26,217 --> 00:31:30,254 Narrator: How can a star have multiple deaths? 608 00:31:30,255 --> 00:31:34,958 The answer lies in its sheer size. 609 00:31:34,959 --> 00:31:37,160 We're talking about a very massive star here, 610 00:31:37,161 --> 00:31:39,930 about 100 or more times the mass of the sun, 611 00:31:39,931 --> 00:31:42,266 really the upper limit of what a star can be 612 00:31:42,267 --> 00:31:44,001 without tearing itself apart. 613 00:31:44,002 --> 00:31:46,737 ♪♪ 614 00:31:46,738 --> 00:31:48,639 Narrator: This star is so big 615 00:31:48,640 --> 00:31:52,342 that reactions in the core are off the charts. 616 00:31:52,343 --> 00:31:54,511 And these energetic reactions 617 00:31:54,512 --> 00:31:57,814 produce more than just elements. 618 00:31:57,815 --> 00:32:00,183 It can actually get so hot in the interior 619 00:32:00,184 --> 00:32:01,752 that you produce gamma rays. 620 00:32:01,753 --> 00:32:06,023 This is the most energetic form of light imaginable. 621 00:32:06,024 --> 00:32:07,991 Narrator: The gamma rays' extreme energy 622 00:32:07,992 --> 00:32:10,060 supports the dying star 623 00:32:10,061 --> 00:32:13,730 against the crushing forces of gravity pushing in, 624 00:32:13,731 --> 00:32:18,168 but it also affects the gamma rays themselves. 625 00:32:18,169 --> 00:32:21,338 Gamma rays above a certain energy can do something weird. 626 00:32:21,339 --> 00:32:24,241 They can transform themselves into matter. 627 00:32:24,242 --> 00:32:26,977 Narrator: This transformation affects the delicate balance 628 00:32:26,978 --> 00:32:31,048 between gravity and energy in the star's core. 629 00:32:31,049 --> 00:32:32,883 The core starts to collapse. 630 00:32:32,884 --> 00:32:35,886 When it collapses, it generates more energy. 631 00:32:35,887 --> 00:32:38,789 This energy leaks out of the outer layers of the star, 632 00:32:38,790 --> 00:32:42,492 and we sudden brightening of the star, a pulse. 633 00:32:42,493 --> 00:32:44,428 ♪♪ 634 00:32:44,429 --> 00:32:47,397 Filippenko: And it brightens and fades a bunch of times, 635 00:32:47,398 --> 00:32:50,267 each time releasing some material 636 00:32:50,268 --> 00:32:53,103 but not quite exploding. 637 00:32:53,104 --> 00:32:56,139 It's almost supernova levels of energy. 638 00:32:56,140 --> 00:33:00,377 That's what fooled the astronomers at first. 639 00:33:00,378 --> 00:33:03,246 Narrator: Eventually, the pulsations stop. 640 00:33:03,247 --> 00:33:07,517 The star calms down, ready to live another day. 641 00:33:07,518 --> 00:33:09,453 ♪♪ 642 00:33:09,454 --> 00:33:13,390 Astronomers still don't know if this "zombie" supernova 643 00:33:13,391 --> 00:33:15,425 has finally died. 644 00:33:15,426 --> 00:33:18,528 Filippenko: We think that we've seen this final explosion 645 00:33:18,529 --> 00:33:20,063 of the zombie supernova, 646 00:33:20,064 --> 00:33:22,566 but honestly, we're not sure yet. 647 00:33:22,567 --> 00:33:25,202 Maybe it's currently fading, but next year, 648 00:33:25,203 --> 00:33:30,073 it'll surprise us and brighten once again. 649 00:33:30,074 --> 00:33:33,710 Narrator: But this isn't the only mysterious supernova 650 00:33:33,711 --> 00:33:36,713 that has scientists scratching their heads. 651 00:33:36,714 --> 00:33:42,185 Meet supernova sn 2014c. 652 00:33:42,186 --> 00:33:45,655 Supernova 2014c was a bit of a strange one. 653 00:33:45,656 --> 00:33:49,226 It was initially classified as a type I. 654 00:33:49,227 --> 00:33:52,496 ♪♪ 655 00:33:52,497 --> 00:33:56,700 Narrator: Astronomers classify supernovas as type I or type ii, 656 00:33:56,701 --> 00:34:01,171 depending on whether they contain hydrogen. 657 00:34:01,172 --> 00:34:03,573 If you break the light up coming in from a supernova 658 00:34:03,574 --> 00:34:06,343 into its individual colors, you take its spectrum. 659 00:34:06,344 --> 00:34:09,212 If there's the signature of hydrogen in that spectrum, 660 00:34:09,213 --> 00:34:11,248 that's a type ii supernova. 661 00:34:11,249 --> 00:34:15,152 If the hydrogen is missing, that's type I. 662 00:34:15,153 --> 00:34:18,889 Narrator: When sn 2014c was first discovered, 663 00:34:18,890 --> 00:34:21,124 hydrogen was missing. 664 00:34:21,125 --> 00:34:24,528 But then later on, hydrogen suddenly appeared, 665 00:34:24,529 --> 00:34:27,497 and we realized, no, this is actually a type ii. 666 00:34:27,498 --> 00:34:29,566 It's sort of a chameleon supernova. 667 00:34:29,567 --> 00:34:33,437 It went from being type I, free of hydrogen, 668 00:34:33,438 --> 00:34:35,872 to type ii, full of hydrogen. 669 00:34:35,873 --> 00:34:37,207 How can a supernova change 670 00:34:37,208 --> 00:34:40,076 from not having hydrogen to having hydrogen? 671 00:34:40,077 --> 00:34:44,648 ♪♪ 672 00:34:44,649 --> 00:34:48,218 Narrator: The chameleon supernova baffled scientists, 673 00:34:48,219 --> 00:34:51,988 until they looked around it with the nustar X-ray telescope. 674 00:34:51,989 --> 00:34:54,458 ♪♪ 675 00:34:54,459 --> 00:34:56,693 It revealed that the star had spewed out 676 00:34:56,694 --> 00:34:59,496 a huge amount of hydrogen. 677 00:34:59,497 --> 00:35:02,232 But this wasn't during the supernova event. 678 00:35:02,233 --> 00:35:05,268 This was many decades before. 679 00:35:05,269 --> 00:35:09,139 This star is very massive and relatively unstable. 680 00:35:09,140 --> 00:35:12,642 And it underwent an explosive event about a century ago -- 681 00:35:12,643 --> 00:35:14,644 not big enough to be a supernova, 682 00:35:14,645 --> 00:35:17,113 but it expelled all the hydrogen in that star, 683 00:35:17,114 --> 00:35:20,050 so it was a type I. 684 00:35:20,051 --> 00:35:23,687 Narrator: Then the star exploded again, 685 00:35:23,688 --> 00:35:26,690 but this event was massive. 686 00:35:26,691 --> 00:35:29,726 Filippenko: The ejected gases from the supernova 687 00:35:29,727 --> 00:35:32,562 smashed into the hydrogen 688 00:35:32,563 --> 00:35:35,065 that had been previously expelled 689 00:35:35,066 --> 00:35:38,635 by the star before exploding. 690 00:35:38,636 --> 00:35:41,905 And once the ejected gases crashed in, 691 00:35:41,906 --> 00:35:45,075 well, that caused that hydrogen gas to glow. 692 00:35:45,076 --> 00:35:47,077 And then we saw hydrogen in the spectrum, 693 00:35:47,078 --> 00:35:50,514 and it became a type ii. 694 00:35:50,515 --> 00:35:53,550 Narrator: The more scientists learn about supernovas, 695 00:35:53,551 --> 00:35:56,219 the more complicated they become. 696 00:35:56,220 --> 00:36:00,957 ♪♪ 697 00:36:00,958 --> 00:36:02,325 Thaller: So, now it seems that we've seen 698 00:36:02,326 --> 00:36:04,327 every type of supernova that must be possible. 699 00:36:04,328 --> 00:36:06,830 And we've seen some very, very strange ones, 700 00:36:06,831 --> 00:36:09,666 things that are zombies or chameleons. 701 00:36:09,667 --> 00:36:13,436 But there has to be something out there that's stranger still. 702 00:36:13,437 --> 00:36:15,739 ♪♪ 703 00:36:15,740 --> 00:36:17,274 Narrator: There may be a whole zoo 704 00:36:17,275 --> 00:36:20,243 of undiscovered supernovas out there -- 705 00:36:20,244 --> 00:36:23,880 exciting, perplexing, deadly. 706 00:36:23,881 --> 00:36:26,683 And they may have been shaping the solar system, 707 00:36:26,684 --> 00:36:30,421 and earth, since the beginning of time. 708 00:36:43,301 --> 00:36:48,505 ♪♪ 709 00:36:48,506 --> 00:36:51,341 Narrator: The death of a giant star -- 710 00:36:51,342 --> 00:36:54,911 it's more than just an epic explosion. 711 00:36:54,912 --> 00:36:57,347 It unleashes a storm of elements 712 00:36:57,348 --> 00:37:00,450 that form the universe around us. 713 00:37:00,451 --> 00:37:03,587 There's a wonderful cycle of death and life in the universe. 714 00:37:03,588 --> 00:37:06,156 Individual stars are born, they live their lives, 715 00:37:06,157 --> 00:37:09,326 and they die. 716 00:37:09,327 --> 00:37:11,494 When they die, they enrich the universe 717 00:37:11,495 --> 00:37:14,531 with new atoms and new chemicals. 718 00:37:14,532 --> 00:37:18,868 Those go on to form new stars and new planets. 719 00:37:18,869 --> 00:37:21,404 Narrator: Dust blows out from the explosion, 720 00:37:21,405 --> 00:37:26,343 forming spectacular interstellar clouds -- nebulas, 721 00:37:26,344 --> 00:37:32,249 the nursery of stars, including our solar system. 722 00:37:32,250 --> 00:37:34,584 One of the biggest pieces of evidence we have 723 00:37:34,585 --> 00:37:36,686 is that supernova themselves 724 00:37:36,687 --> 00:37:41,124 produce some very rare radioactive elements, 725 00:37:41,125 --> 00:37:44,027 radioactive elements that we can still see 726 00:37:44,028 --> 00:37:46,796 embedded in the solar system today. 727 00:37:46,797 --> 00:37:51,401 It's sprinkled like radioactive salt. 728 00:37:51,402 --> 00:37:53,236 Narrator: These radioactive elements, 729 00:37:53,237 --> 00:37:57,807 found right across our planet, are only produced in supernovas, 730 00:37:57,808 --> 00:38:00,510 proof that earth and the solar system 731 00:38:00,511 --> 00:38:02,612 were created from exploding stars 732 00:38:02,613 --> 00:38:06,716 4.6 billion years ago. 733 00:38:06,717 --> 00:38:09,552 But supernovas may have affected earth 734 00:38:09,553 --> 00:38:12,856 much more recently. 735 00:38:12,857 --> 00:38:14,157 We do have some evidence 736 00:38:14,158 --> 00:38:17,193 that there was a particular supernova explosion 737 00:38:17,194 --> 00:38:21,398 that rained down on the earth about 2 1/2 million years ago 738 00:38:21,399 --> 00:38:25,502 and deposited a specific kind of iron. 739 00:38:25,503 --> 00:38:28,371 Narrator: Iron-60 is a radioactive element 740 00:38:28,372 --> 00:38:30,774 made during supernova. 741 00:38:30,775 --> 00:38:35,679 It's found in fossils from around this time. 742 00:38:35,680 --> 00:38:39,749 We see it embedded in the crust of the earth itself. 743 00:38:39,750 --> 00:38:43,620 We see pieces of evidence. 744 00:38:43,621 --> 00:38:45,889 Narrator: 2 1/2 million years ago, 745 00:38:45,890 --> 00:38:49,325 life on earth changed dramatically. 746 00:38:49,326 --> 00:38:53,830 Africa lost much of its forests to grasslands, 747 00:38:53,831 --> 00:38:57,333 various plants and animals went extinct, 748 00:38:57,334 --> 00:39:00,370 and many new species appeared. 749 00:39:00,371 --> 00:39:03,573 But how could a supernova change life on earth 750 00:39:03,574 --> 00:39:08,344 so dramatically without destroying it completely? 751 00:39:08,345 --> 00:39:11,114 ♪♪ 752 00:39:11,115 --> 00:39:12,415 When a supernova explodes, 753 00:39:12,416 --> 00:39:15,118 it produces a tremendous amount of gamma rays. 754 00:39:15,119 --> 00:39:17,353 And if that supernova is close enough to the earth, 755 00:39:17,354 --> 00:39:22,092 you could imagine it really doing damage to our atmosphere. 756 00:39:22,093 --> 00:39:24,327 Narrator: Some of the incredible amounts of energy 757 00:39:24,328 --> 00:39:26,062 found in a supernova 758 00:39:26,063 --> 00:39:30,366 leave the star in gamma-ray beams. 759 00:39:30,367 --> 00:39:33,036 If that beam were to be pointing at earth, 760 00:39:33,037 --> 00:39:35,672 then the ozone layer could be harmed. 761 00:39:35,673 --> 00:39:44,114 ♪♪ 762 00:39:44,115 --> 00:39:52,555 ♪♪ 763 00:39:52,556 --> 00:39:54,457 It affects our ozone layer, 764 00:39:54,458 --> 00:39:57,260 which affects the amount of U.V. radiation 765 00:39:57,261 --> 00:40:00,430 that can hit the surface, which can trigger mutations, 766 00:40:00,431 --> 00:40:03,233 which can trigger different forms of vegetation, 767 00:40:03,234 --> 00:40:05,835 which can kill off algae in the in the oceans. 768 00:40:05,836 --> 00:40:08,805 There's a lot of potential effects. 769 00:40:08,806 --> 00:40:12,976 Narrator: Mutations drive evolution in all forms of life, 770 00:40:12,977 --> 00:40:17,180 from the simplest to the most complex. 771 00:40:17,181 --> 00:40:19,949 So it's conceivable that, as a result 772 00:40:19,950 --> 00:40:22,986 of a relatively nearby supernova, 773 00:40:22,987 --> 00:40:25,855 the mutations led to early hominids 774 00:40:25,856 --> 00:40:28,324 and then homo sapiens. 775 00:40:28,325 --> 00:40:32,428 That actually affected the evolution of life on earth, 776 00:40:32,429 --> 00:40:34,531 and humans in particular. 777 00:40:34,532 --> 00:40:37,934 ♪♪ 778 00:40:37,935 --> 00:40:40,904 Narrator: Is it just coincidence that ancient humans 779 00:40:40,905 --> 00:40:43,807 started to appear at around this time? 780 00:40:43,808 --> 00:40:50,013 Or was our humanity sparked by a supernova? 781 00:40:50,014 --> 00:40:52,982 Supernovas seem to be an example of violent death. 782 00:40:52,983 --> 00:40:55,785 But there were so many steps in the formation 783 00:40:55,786 --> 00:40:57,987 of our solar system, the formation of you, 784 00:40:57,988 --> 00:41:00,390 that are intimately related to supernova. 785 00:41:00,391 --> 00:41:01,591 They created the chemical elements 786 00:41:01,592 --> 00:41:03,326 and maybe even drove our evolution. 787 00:41:03,327 --> 00:41:05,295 We very likely would not exist 788 00:41:05,296 --> 00:41:07,864 if it were not for exploding stars. 789 00:41:07,865 --> 00:41:11,901 Narrator: From the elements in our DNA to the solar system 790 00:41:11,902 --> 00:41:16,372 and the world we live in, supernovas have made us. 791 00:41:16,373 --> 00:41:18,208 Thaller: The reason we study astronomy at all 792 00:41:18,209 --> 00:41:21,177 is to actually answer the question as to who we are, 793 00:41:21,178 --> 00:41:23,313 where we came from, and we're going. 794 00:41:23,314 --> 00:41:25,215 And with supernovas, that's all wrapped up 795 00:41:25,216 --> 00:41:27,350 into this amazing story. 796 00:41:27,351 --> 00:41:31,054 Literally, you are the death of a star. 797 00:41:31,055 --> 00:41:33,656 Narrator: These epic explosions 798 00:41:33,657 --> 00:41:38,294 are unlocking the biggest mysteries of our existence. 799 00:41:38,295 --> 00:41:40,964 The story of supernova have become more interesting 800 00:41:40,965 --> 00:41:42,866 and more complex with every discovery. 801 00:41:42,867 --> 00:41:44,834 So as we learn more, we discover 802 00:41:44,835 --> 00:41:47,403 what it is that we don't understand yet. 803 00:41:47,404 --> 00:41:50,406 Tremblay: The cosmos is something that can seem so distant 804 00:41:50,407 --> 00:41:53,977 and so unreachable, but stars are the things, 805 00:41:53,978 --> 00:41:55,645 the brilliant light to the cosmos, 806 00:41:55,646 --> 00:42:00,016 with which we have the most strong connection. 807 00:42:00,017 --> 00:42:03,653 There are so many things to love about exploding stars. 808 00:42:03,654 --> 00:42:07,957 They are what give rise to the elements of life. 809 00:42:07,958 --> 00:42:09,959 ♪♪ 810 00:42:09,960 --> 00:42:13,463 From the most intimate to the most gigantic scales imaginable, 811 00:42:13,464 --> 00:42:17,967 supernovas are the key to all of that. 812 00:42:17,968 --> 00:42:20,203 So, thank you, supernova. 813 00:42:20,204 --> 00:42:21,471 Hats off to you. 814 00:42:21,472 --> 00:42:24,808 Now, please, stay very, very far away.