How the Universe Works - S07E02 - When Supernovas Strike
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00:00Supernovas, gigantic explosions that light up the cosmos.
00:13One of the most spectacular things in the universe is the death of a giant star.
00:18They live fast and they die young.
00:22Inside, the star's core temperature and pressures are immense.
00:28We're talking about a billion degrees in the center of one of these stars.
00:33A ticking time bomb that explodes with indescribable energy.
00:39The last minutes of a giant star's life are the most cataclysmic events that we see in the universe.
00:51Dramatic finales blazing across space.
00:56That one supernova is brighter than the hundreds of billions of stars that constitute the galaxy.
01:02How amazing is that?
01:04But these stellar deaths also hold the key to life itself.
01:10Understanding supernovas is understanding our story.
01:14We owe our existence to them.
01:26Right now, somewhere in the universe, a giant star is detonating.
01:38Creating a huge cosmic explosion called a supernova.
01:48Supernovas are a big, giant, dramatic end to a star's life.
01:59All stars die, but only the biggest go out with a bang.
02:04For a star to go supernova, we think it has to be at least eight times more massive than our sun.
02:11It's so easy to think of our sun as this incredibly gigantic thing.
02:15But our sun is absolutely tiny compared to some of the giant stars in the sky.
02:26We can see some of these giant stars with the naked eye.
02:31And the 10th brightest in the night sky is a red supergiant around 15 times the mass of the sun, Betelgeuse.
02:43Betelgeuse is so big that if you were to place it in our own solar system, it would stretch to the orbit of Jupiter.
02:52This is one of the biggest beasts in the galaxy.
02:55It's a star also that is on the verge of death.
03:01Betelgeuse is less than 10 million years old.
03:05But this huge star's days are numbered.
03:09It's ready to blow.
03:14And when it does, we'll see a region of sky brighten for 14 days until it's nearly as bright as a full moon.
03:23It is going to be one of the most spectacular shows in history.
03:30And it could happen at any moment.
03:32When I'm flying, I often stand outside in my yard in the wintertime.
03:35I look up at Orion and I see Betelgeuse.
03:37And I'm like, explode.
03:41So, what will make Betelgeuse go supernova?
03:46To understand a giant star's death, we need to understand its life.
03:53From the day it's born until the day it dies, a star's life is a constant battle.
04:02Gravity is pulling in and energy pushing out.
04:07The interior of a star is fusing countless atomic nuclei together.
04:12Atoms are ramming into each other, getting very, very close.
04:17And if they get close enough, they'll actually stick and form a larger atom.
04:22Every second, a giant star fuses 7.5 billion tons of hydrogen.
04:28That amount of energy is roughly equivalent to about 100 billion atomic bombs per second.
04:34That's a big-ass explosion.
04:38This explosive energy threatens to blow the star apart.
04:44But the star's own massive gravity keeps the lid on.
04:49Everything in the universe is a fight between the inward force of gravity and the outward force of pressure or energy.
04:57Every single star in the sky, even our own sun, is an incredibly dynamic battleground.
05:01In many ways, stars are an explosion that are actually too big to explode.
05:05Gravity holds it together.
05:09This battle between these two opposing forces determines the life and death of the star.
05:16And this is where size matters.
05:19The more massive the star, the more gravity pushes inward.
05:24The harder the star has to push outward to keep itself alive.
05:31Very massive stars are like stars on steroids.
05:35They have a lot of fuel to burn.
05:38They're so powerful that they use up their fuel at a rapid rate.
05:45Massive stars, like Betelgeuse, are giant factories fusing lighter elements into heavier ones.
05:53But the hard work doesn't start until their final years.
05:58For around 90% of their life, they fuse hydrogen into helium.
06:03But eventually, the hydrogen starts running out.
06:08In the core of a supergiant star, there's a sequence of fusion that goes from lighter elements to heavier elements.
06:14And it gets faster and faster every step of the way.
06:18The countdown to death begins.
06:22An upward push from gravity takes over, raising the temperature in the core.
06:27Helium starts fusing into carbon.
06:31There's enough helium to last about a million years.
06:34But it, too, runs out and things start speeding up.
06:40Carbon gets fused into neon. That takes about 1,000 years.
06:44Neon fusing into silicon, that takes about one year.
06:47Once it starts fusing silicon into iron, that takes one day.
06:52It gets more and more frantic. It's kind of like a cooking contest show.
06:56Whereas the clock is running down, they're trying to do more and more things and they get more and more frantic until, ding, time's up.
07:06The star is now in its death throes.
07:10Once iron production has started, the clock is ticking towards the cataclysmic end of this star.
07:20A giant ball of incredibly dense iron forms in the middle of the dying star's core.
07:27This iron sphere is several thousand miles across and unbelievably hot.
07:34It gets so hot there, the temperature almost becomes meaningless.
07:38I mean, we're talking about a billion degrees in the center of one of these stars.
07:47This extreme heat is caused by fusion reactions.
07:51More and more reactions create heavier and heavier elements.
07:55And with each step, less and less energy is produced until iron is created.
08:02When you try to fuse iron nuclei together, that takes energy. It doesn't generate energy.
08:07So once the core starts to fuse iron, it's basically stealing its own energy.
08:13The growing iron core sucks more and more energy from the star.
08:17Gravity continues pulling in, overwhelming the outward pressure from inside the star.
08:27Everything gets crushed to unimaginable degrees.
08:30All of a sudden, there's no nuclear reaction to support the star against the crush of gravity.
08:38With nothing left holding it up, the star is doomed.
08:43Gravity wins. The edges of the iron core collapse.
08:48Trillions of tons of dense iron fall inward at a quarter of the speed of light.
08:54The star has now less than one second left to live.
08:58Things start to fall apart really quickly.
09:03The core collapse is so fast that the outer layers of the star don't even have time to react.
09:08They're just hanging there.
09:09It's kind of like Wile E. Coyote when a cliff collapses underneath him and he doesn't even fall until he notices.
09:17The rest of the star collapses.
09:19A trillion, trillion, trillion tons of gas hurtle inwards following the iron.
09:26Think about the entire mass of the star that has been held up by nuclear reactions inside.
09:31All of a sudden, those nuclear reactions go away in a split second.
09:35Everything rushes into the middle.
09:39And that sets off the most dramatic explosion in the universe.
09:50The spectacular death blow can outshine all of the stars in the galaxy.
09:57But there's a problem.
09:59We still don't fully understand how a collapsing ball of iron and tons of falling gas create a giant fireball.
10:09How this collapsing core triggers a massive explosion is one of the biggest mysteries in astrophysics.
10:30A supernova, one of the most powerful eruptions in the cosmos, triggered by the collapse of a massive star.
10:39How do you go from a violent collapse to an incredibly dramatic explosion?
10:44This involves some of the most complex astrophysics known to humanity.
10:49And we don't fully understand the details of the process.
10:53We're missing something because we nearly always spot supernovas too late.
10:58What you're seeing is you're seeing the star brightening, and that's really happening after the fact.
11:02So now the magic key is not finding a supernova, but finding the moment that we call the breakout.
11:15The breakout is a giant star's death rattle.
11:18It's the moment after the core has collapsed when the star blows apart in a huge flash of visible light.
11:28But in the entire history of astronomy, this moment has only been caught twice.
11:34Once by NASA's multi-million dollar space telescope, Kepler, and once by a very lucky Argentinian amateur.
11:43I love this story. There's an amateur astronomer named Victor Busso.
11:45He has a very nice telescope in an observatory in his yard.
11:49And he was taking photographs repeatedly of the same galaxy that happened to be overhead.
11:54And he just happened to be looking at the right region of the sky,
11:57and he luckily caught the shock breakout of a supernova.
12:05The chances of catching this moment are slim.
12:09The chances of catching this moment? One in ten million.
12:14What Victor caught was the moment the shock wave reaches the surface.
12:20Victor noticed this spot appearing in his photographs.
12:24Realizing he'd captured the first flash of light from an exploding star,
12:29he alerted professional astronomers across the globe.
12:32When I heard of his discovery, I was like, no way.
12:36How could this guy, using a camera on his telescope for the very first time,
12:41pointing at a single random galaxy in the sky,
12:45have found this exploding star in the first hour of its explosion?
12:50It's almost too good to be true.
12:53Alex Filippenko and his team monitored the blast.
12:58Alex Filippenko and his team monitored the brightening light from the star.
13:04What we found when studying the light from Busso's supernova
13:08is that the object brightened very quickly for a short time
13:13when a shock wave, a supersonic wave going through the star,
13:18burst out through the surface.
13:21And when it gets right to the edge,
13:24that huge amount of energy is released as a tremendous flash.
13:28That is the moment of shock breakout.
13:33The monstrous shock wave travels at nearly 30,000 miles per hour,
13:38bursting through the surface of the star and ripping it to pieces.
13:42Fire!
13:44We see shock waves from explosions on Earth.
13:47They can travel through gas, liquid, and solid,
13:51including the layers of a collapsing star.
13:57This observation of the shock wave reaching the surface of the star
14:00was incredibly important, because Victor managed to catch a star
14:04the moment it actually went supernova.
14:06That is something that is astounding.
14:08Because Victor managed to catch a star the moment it actually went supernova.
14:12That is something that is a scientific treasure.
14:16The shock breakout is like cosmic gold dust,
14:20a flash in the pan that lasts 20 minutes,
14:25just a blink of the eye on astronomical timescales.
14:31But what sets the shock wave off?
14:33Is it just a question of bounce?
14:36A supernova shock wave can be explained with the help of a basketball.
14:41The thing about an exploding star is that the nuclear reactions go out in the core,
14:46and then the outer layers fall in at incredibly high speeds toward the inner core,
14:51and then it rebounds and bounces out.
14:54And what gives it so much energy is the structure of the star.
15:00As the dying star burns through its fuel,
15:03it creates layers of different elements,
15:06heavy iron at the core, with layers and layers of lighter elements above.
15:11So let's say there was only one layer, and there was a rebound, like dropping this ball.
15:16It doesn't bounce very high, but let's say it's organized like a star,
15:20where the heavy thing is at the bottom, the lighter thing is at the top.
15:23And let's see how this rebound goes.
15:27Now that was a rebound.
15:31The tennis ball launches off the basketball
15:34because energy from the basketball's bounce is transferred upwards.
15:39The same thing happens at a collapsing star, but with many more layers.
15:44All the different elements collapse inwards.
15:47The heavier layers hit the dense core first, passing energy to the outer core.
15:53And this creates the shockwave.
15:57But this energy isn't enough to propel the shockwave all the way out of the star.
16:03The problem is, when we looked at this in detail using computer models, it didn't work.
16:08The shockwave seemed to stall. We couldn't get the star to explode.
16:12For 50 years, we couldn't figure out what we were missing.
16:16Scientists suspect something is wrong.
16:20Scientists suspect something else is involved.
16:23Something that's almost impossible to detect.
16:26Could there be a ghost in the supernova machine?
16:43When stars as big as Betelgeuse die,
16:46their explosive deaths send shockwaves that travel trillions of miles through space.
16:52But how these shockwaves are created has puzzled scientists for decades.
16:58Time and time again, when we actually went back to our computers and our theories
17:02and looked at how supernovas should work, they just didn't.
17:05They shouldn't actually explode.
17:08In computer models, the bounce from falling gas and the collapsing core
17:13can't drive the shockwave all the way out of the star.
17:17Something crucial is missing.
17:20What we needed from inside the core of the star was a completely new source of energy.
17:25Something to actually make that final push to get the star to rip itself apart.
17:31Scientists suspect this energy comes from an enigmatic particle called a neutrino.
17:38Neutrinos are a type of fundamental physical particle that are still a little bit mysterious to us.
17:44They're almost like ghost particles. They travel through us without touching us at all.
17:52Like particles of light, photons, neutrinos carry no electrical charge.
17:58But, unlike photons, they can pass through stars, planets, and us.
18:05So, where do they come from?
18:07Scientists predict the source is the star itself.
18:13In the middle of the core of a star, you're producing something called a neutron star,
18:17an amazing super-compressed ball of matter only about 10 miles across.
18:23As the iron core of a star collapses, the atoms are crushed together.
18:28Protons and electrons are forced to combine to form neutrons.
18:33This process releases vast quantities of neutrinos.
18:41Despite being one of the most abundant particles in the universe, neutrinos are notoriously difficult to detect.
18:53But in 1987, scientists got lucky.
18:58A massive star went supernova in a nearby galaxy.
19:05In 1987, astronomers got a wonderful gift.
19:09It was the first naked-eye supernova in about 400 years.
19:15And we had lots and lots of telescopes with which to study it throughout the electromagnetic spectrum.
19:23But the 1987 A supernova set off another scientific instrument,
19:30a neutrino detector hidden deep below a mountain in Japan.
19:36There was a burst of neutrinos associated with a supernova.
19:40This was just a fantastic surprise, a wonderful added bonus.
19:45When you're trying to capture and measure elusive particles
19:50that you don't even know if you're going to get a signal or not,
19:53and you're just sitting there waiting at your detector,
19:55and then suddenly this thing just lights up, how exciting is that?
20:01This was definitive proof that supernovas emit neutrinos.
20:08Neutrinos may be ghostly, but they don't gently drift out from the collapsing core of the star.
20:14They have to burst out.
20:16The amazing thing about the inside of a supernova explosion
20:19is that it's getting dense enough to trap neutrinos.
20:23All of a sudden now there's pressure.
20:28When scientists add neutrino pressure to the computer models,
20:32the shockwave gets farther away from the core.
20:35But the supernova still doesn't explode.
20:38One more ingredient is needed.
20:41Disorder.
20:43Because stars are round,
20:46it's tempting to think that a supernova explosion too will be round.
20:52But supernova aren't perfectly symmetric.
20:57Energy from the shockwave and the neutrinos
21:00heats up the gas in chaotic, unpredictable ways.
21:04They cause hot bubbles to rise and then come back down,
21:08and rise and come back down.
21:10It's sort of a boiling motion.
21:12This imparts a lot of turbulence into the gas.
21:15Researchers add all the ingredients to a supercomputer and let it run.
21:23The result is this simulation.
21:27When the shockwave stalls on its way out of the core,
21:30it creates tiny ripples in the falling elements above.
21:34The ripples become giant, sloshing waves.
21:38Neutrinos, bursting out from the neutron star,
21:41heat the layers of elements above it,
21:44causing them to bubble and rise.
21:49Eventually, the intense heat combines with the pressure of these violent motions,
21:55driving the shockwave out like an interstellar tsunami,
22:00smashing the star to pieces.
22:09It turns out, stars do explode.
22:12Nature knows what it's doing.
22:14It was the computer models.
22:16They were too simple.
22:17Once the models became more complex,
22:19started taking into account all the dimensions of a star,
22:22the supernova models started to explode.
22:25We think of supernova as effectively simple events,
22:28very violent events, but simple.
22:30And this is just a beautiful illustration of the fact that
22:33when you dig deep down,
22:35these are really exquisitely complex and elegant fluid dynamics problems.
22:41The shockwave travels through all the layers of elements that make up the massive star.
22:47It takes hours for it to reach the outer edge and trigger the first flash of light.
22:53But this flash is just the start of the supernova.
22:57The spectacular light show is just beginning.
23:00A light show that will create elements essential for life.
23:24We see the light from supernovas all the way across the cosmos.
23:30But what we're seeing isn't the explosive first flash.
23:34That's just the opening act before the main event.
23:40Supernova are some of the most energetic events in the universe.
23:45The galaxy has hundreds of billions of stars in it,
23:48and yet the death of this one star can outshine those hundred billions of stars.
23:53One of the interesting things about supernovas is that
23:57when the star explodes, it's not at its maximum brightness immediately.
24:02It takes days and weeks.
24:11The first flash is the explosive part of a supernova,
24:15blasting tons of matter into space around the dying star.
24:20But it's this ejected debris that makes supernovas shine,
24:25often glowing brighter than the explosion itself.
24:32Heavy elements are formed inside the cores of massive stars,
24:36and even heavier elements are formed during the explosion event itself.
24:45As the star rips apart, temperatures and pressures are immense.
24:50The elements that once made up the layers of the star
24:53fuse together, creating heavier elements.
24:56And some of these are radioactive.
25:00The decay of these radioactive elements actually produces light
25:04that gives it more brightness over a longer period of time than it otherwise would have.
25:12This cloud of brightly shining matter can last for months and sometimes years.
25:19These supernova remnants light up the universe like cosmic fireworks.
25:27These are oftentimes beautiful, beautiful things in the night sky
25:32because you see remnants of everything that this supernova has generated in its explosion.
25:40But these are more than pretty light shows.
25:43They're crucial for the evolution of galaxies and solar systems.
25:49Necessary ingredients, things like sulfur, things like phosphorus,
25:55things like carbon and oxygen,
25:58and even the elements necessary to build a rocky planet like the Earth itself,
26:03can only be formed inside of massive stars
26:06and can only be spread through supernova explosions.
26:14NASA's Chandra Space Telescope studies one of the most famous objects in the Milky Way,
26:24supernova remnant Cassiopeia A.
26:30Cassiopeia A is a relatively young supernova remnant, not even 400 years old.
26:36Ever since its star exploded, Cassiopeia A,
26:40has been expanding. It's now 29 light years across.
26:46Using x-rays, the Chandra Space Telescope has looked inside this massive cloud.
26:53New observations of Cassiopeia A have shown us that the ejecta from this event
26:58has created tens of thousands of times the Earth's mass of really important materials.
27:0470,000 Earth masses worth of iron,
27:08and a whopping one million Earth masses worth of oxygen.
27:12Now, these are elements that are important to life, to Earth, to us.
27:17The iron in your blood, the calcium in your bones,
27:20these were forged in supernova explosions billions of years ago.
27:27The new study reveals that the iron in your blood,
27:31The new study reveals something even more extraordinary.
27:37Cassiopeia A also holds the building blocks of life.
27:43We see every single atom necessary for DNA in that one supernova remnant.
27:48One of the really cool things about supernovas is that our very existence depends on them.
27:53Our DNA molecules are made up of material that was once in the core of a massive star.
27:59So somewhere out there, some unnamed supernova eons ago
28:03led to you watching me talking about supernovas. That's awesome.
28:12Supernovas create all the elements needed to build everything from planets to humans.
28:18Dying stars give us life.
28:21It's a cosmic recycling process.
28:24But what if some stars are faking their own deaths?
28:41For thousands of years, supernovas have been a source of life.
28:46For thousands of years, humans have wondered about bright new stars appearing in the sky.
28:52And supernovas continue to surprise us.
28:56Our fascination with supernova has grown with each discovery of a new event.
29:03The study of supernovas is really going through a revolution.
29:07We're learning more and more. We're better able to find them and observe them.
29:12As it turns out, not all supernovas are the same.
29:16Some are the result of white dwarf stars stealing matter from a twin.
29:21And growing so big, they explode.
29:31All other supernovas are massive stars collapsing under their own gravity.
29:42But just to confuse things further, scientists also categorize supernovas based on whether hydrogen is present.
29:50Type I are missing hydrogen. Type II are not.
29:55So astronomers have these categories for supernova.
29:58And that might make you think that we've got them all figured out.
30:01But here's a spoiler. We don't.
30:05September, 2014.
30:08A supernova appears in the Great Bear constellation and glows brightly for 600 days.
30:15When scientists check the records, they discover a supernova was sighted at the exact same spot 60 years before.
30:24A star seemed to be dying over and over again.
30:29This particular star was something we had never seen before.
30:32And it seemed so strange, it was almost impossible.
30:35It actually brightened and faded about five times over a several-year time span.
30:41And each of these brightenings would have qualified as a supernova in terms of its total energy.
30:48It's the supernova that would never die.
30:52So how could it happen with the same star?
30:55This really did seem to be a zombie star.
30:59How can a star have multiple deaths?
31:02The answer lies in its sheer size.
31:07We're talking about a very massive star here, about a hundred or more times the mass of the sun.
31:12Really the upper limit of what a star can be without tearing itself apart.
31:16This star is so big that reactions in the core are off the charts.
31:21And these energetic reactions produce more than just elements.
31:26It can actually get so hot in the interior that you produce gamma rays.
31:30This is the most energetic form of light imaginable.
31:35The supernova is a supernova.
31:37And it's a supernova that's going to go off the charts.
31:40The gamma rays' extreme energy supports the dying star against the crushing forces of gravity pushing in.
31:47But it also affects the gamma rays themselves.
31:51Gamma rays above a certain energy can do something weird.
31:54They can transform themselves into matter.
31:57This transformation affects the delicate balance between gravity and energy in the star's core.
32:04The core starts to collapse.
32:06When it collapses, it generates more energy.
32:09This energy leaks out of the outer layers of the star, and we see a sudden brightening of the star, a pulse.
32:17And it brightens and fades a bunch of times, each time releasing some material,
32:23but not quite exploding the outer layers of the star.
32:28Each time releasing some material, but not quite exploding.
32:33It's almost supernova levels of energy.
32:36That's what fooled the astronomers at first.
32:40Eventually, the pulsations stop.
32:43The star calms down, ready to live another day.
32:49Astronomers still don't know if this zombie supernova has finally died.
32:55We think that we've seen this final explosion of the zombie supernova,
33:00but honestly, we're not sure yet.
33:02Maybe it's currently fading, but next year it'll surprise us and brighten once again.
33:10But this isn't the only mysterious supernova that has scientists scratching their heads.
33:16Meet Supernova SN 2014c.
33:22Supernova 2014c was a bit of a strange one.
33:26It was initially classified as a Type I.
33:32Astronomers use Type I and Type II to identify whether a supernova contains hydrogen.
33:41If you break the light up coming in from a supernova into its individual colors, you take its spectrum.
33:46If there's the signature of hydrogen in that spectrum, that's a Type II supernova.
33:51If the hydrogen is missing, that's Type I.
33:55When SN 2014c was first discovered, hydrogen was missing.
34:01But then later on, hydrogen suddenly appeared, and we realized, no, this is actually a Type II.
34:07It's sort of a chameleon supernova.
34:09It went from being Type I, free of hydrogen, to Type II, full of hydrogen.
34:15How can a supernova change from not having hydrogen to having hydrogen?
34:24The chameleon supernova baffled scientists until they looked around it with the NuSTAR X-ray telescope.
34:34It revealed that the star had spewed out a huge amount of hydrogen.
34:39But this didn't happen during the supernova event.
34:42This happened many decades before.
34:45This star is very massive and relatively unstable, and it underwent an explosive event about a century ago.
34:52Not big enough to be a supernova, but it expelled all the hydrogen in that star, so it was a Type I.
35:00Then the star exploded again, but this event was massive.
35:07The ejected gases from the supernova smashed into the hydrogen that had been previously expelled by the star before exploding.
35:19And once the ejected gases crashed in, well, that caused that hydrogen gas to glow.
35:25And then we saw hydrogen in the spectrum, and it became a Type II.
35:30The more scientists learn about supernovas, the more complicated they become.
35:40So now it seems that we've seen every type of supernova that must be possible,
35:44and we've seen some very, very strange ones, things that are zombies or chameleons.
35:49But there has to be something out there that's stranger still.
35:54There may be a whole zoo of undiscovered supernovas out there.
35:58Exciting, perplexing, deadly.
36:02And they may have been shaping the solar system and Earth since the beginning of time.
36:24The death of a giant star.
36:26It's more than just an epic explosion.
36:29It unleashes a storm of elements that form the universe around us.
36:35There's a wonderful cycle of death and life in the universe.
36:38Individual stars are born, they live their lives, and they die.
36:44When they die, they enrich the universe with new atoms and new chemicals.
36:50Those go on to form new stars and new planets.
36:54Dust blows out from the explosion, forming spectacular interstellar clouds.
37:00Nebulas. The nursery of stars, including our own solar system.
37:07One of the biggest pieces of evidence we have is that supernovae themselves
37:12produce some very rare radioactive elements,
37:16which means radioactive elements that we can still see embedded in the solar system today.
37:22It's sprinkled like radioactive salt.
37:27These radioactive elements found right across our planet are only produced in supernovas,
37:33proof that Earth and the solar system were created from exploding stars 4.6 billion years ago.
37:41But supernovas may have affected Earth much more recently.
37:47We do have some evidence that there was a particular supernova explosion
37:52that rained down on the Earth about two and a half million years ago
37:56and deposited a specific kind of iron.
38:01Iron-60 is a radioactive element made during a supernova.
38:06It's found in fossils from around this time.
38:11We see it embedded in the crust of the Earth itself. We see pieces of evidence.
38:19Two and a half million years ago, life on Earth changed dramatically.
38:24Africa lost much of its forests to grasslands.
38:28Various plants and animals went extinct, and many new species appeared.
38:36But how could a supernova change life on Earth so dramatically without destroying it completely?
38:46When a supernova explodes, it produces a tremendous amount of gamma rays.
38:50And if that supernova is close enough to the Earth, you could imagine it really doing damage to our atmosphere.
38:57Some of the incredible amounts of energy found in a supernova leave the star in gamma ray beams.
39:05If that beam were to be pointing at Earth, then the ozone layer could be harmed.
39:11Explosion
39:27It affects our ozone layer, which affects the amount of UV radiation that can hit the surface,
39:33which can trigger mutations, which can trigger different forms of vegetation,
39:38which can kill off algae in the oceans. There's a lot of potential effects.
39:44Mutations drive evolution in all forms of life, from the simplest to the most complex.
39:52So it's conceivable that as a result of a relatively nearby supernova,
39:57the mutations led to early hominids and then homo sapiens.
40:03That actually affected the evolution of life on Earth and humans in particular.
40:13Is it just coincidence that ancient humans started to appear at around this time?
40:18Or was our humanity sparked by a supernova?
40:25Supernovas seem to be an example of violent death,
40:28but there were so many steps in the formation of our solar system, the formation of you,
40:33that are intimately related to supernova.
40:35They created the chemical elements and maybe even drove our evolution.
40:38We very likely would not exist if it were not for exploding stars.
40:43From the elements in our DNA to the solar system and the world we live in, supernovas have made us.
40:51The reason we study astronomy at all is to actually answer the question as to who we are,
40:56where we came from and where we're going.
40:58And with supernovas, that's all wrapped up into this amazing story.
41:02Literally, you are the death of a star.
41:07These epic explosions are unlocking the biggest mysteries of our existence.
41:13The story of supernova have become more interesting and more complex with every discovery.
41:18So as we learn more, we discover what it is that we don't understand yet.
41:22The cosmos is something that can seem so distant and so unreachable.
41:27But stars are the things, the brilliant light to the cosmos with which we have the most strong connection.
41:35There are so many things to love about exploding stars.
41:38They are what give rise to the elements of life.
41:45From the most intimate to the most gigantic scales imaginable, supernovas are the key to all of that.
41:53So thank you, supernova. Hats off to you.
41:56Now please stay very, very far away.