How the Universe Works - S01E06 - Planets
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00:00This is an exploding star. It's called a supernova.
00:13A supernova is the greatest cataclysm in the history of the entire universe.
00:19Supernovas come in different sizes and types. All of them are so bright, they can be seen across the universe.
00:28A supernova is the most violent death of a star you can imagine.
00:34But this violent destruction of a star is also the birth of everything we see around us.
00:43Really big stars go out with a bang, called a supernova.
01:02A supernova can outshine an entire galaxy, releasing trillions of times the energy of our sun.
01:14They're so violent, if one of them exploded just a few dozen light-years away, planet Earth would be toast.
01:27A nearby supernova would really ruin our day.
01:43First of all, the sudden burst of radiation would scorch the atmosphere.
01:49The only place to go is underground.
01:54Underground, you could then withstand the blistering burst of x-rays which hit the Earth, and then it would scorch all plant life.
02:02And with the collapse of the food chain, we're talking about a possible extinction on the Earth.
02:12Supernovas are killers.
02:20But they also create the basic elements that make up our world.
02:28Our planet, our star, everything around us formed out of the debris of a dead, exploded star.
02:36Everything that makes up our bodies and the skyline came from supernovae.
02:44All of the iron, all of the silicon, all of the elements that went into these buildings.
02:49The things that make up my blood, my body, the gold in my wedding ring.
02:53Everything you see here is a supernova.
03:05But our sun won't become a supernova.
03:07It's too small.
03:21Like all stars, it's basically a giant nuclear reactor.
03:29The fusion reactor inside a star burns hydrogen, the simplest, most common element.
03:39The reaction fuses hydrogen atoms together, producing helium and energy.
03:54And when the hydrogen runs out, stars keep burning by fusing helium into carbon, then carbon into oxygen.
04:07When small stars like our sun make carbon, they begin to die.
04:13During the lifetime of a star, there's a balance between gravity pulling in and pressure pushing out.
04:18For a star that's generating energy, there's no problem.
04:22But once energy generation switches off, the pressure goes away and gravity wins.
04:30Now gravity begins to crush the center of the star.
04:39The star's outer layers are pushed outwards.
04:46They expand into a huge ball of gas called a red giant.
04:53Our sun, when it dies, four and a half to five billion years from now, it's corona will go all the way out to Mars.
05:05Everything on the planet Earth will vaporize.
05:15While the outer layers expand, in the center of the sun, gravity will have the opposite effect.
05:26It'll crush the sun's core to just a millionth of its original size, about the size of the Earth.
05:34Now it's a dense ball of oxygen and carbon called a white dwarf.
05:46In our solar system, this will be the end of the story.
05:51The gas from the dying star will gradually disperse, but the tiny white dwarf will burn for billions of years.
06:05But our solar system is unusual. It has just one star.
06:16The fact is, the vast majority of stars orbit in pairs.
06:27When one of the two stars dies and becomes a white dwarf, if it's close enough, it starts stealing material from the other star.
06:46Think of two stars rotating around each other.
06:51One star slowly sucking all the hydrogen and helium from its companion star.
06:58It's like a vampire.
07:03As the white dwarf sucks more and more fuel out of its companion star, it gets heavier and denser and less stable.
07:15Carbon and oxygen atoms are about to fuse together, and that's bad news.
07:27A white dwarf, in some sense, is like a bomb waiting to be lit.
07:34There's a huge amount of energy stored in that star, gravitational energy and nuclear energy.
07:42This white dwarf is turning into a monster, a type 1A monster.
07:48A type 1A supernova is a 20 billion billion billion megaton thermonuclear carbon bomb.
07:56It's one of the most explosive substances in the universe.
08:03Eventually, the white dwarf drains so much material from its companion, it goes into nuclear overload.
08:16The carbon and oxygen inside it start to turn into a common but dangerous element, at least to stars.
08:27You've probably seen in Star Trek the idea that there's some sort of secret technology that kills a star.
08:32Well, I mean, it's in your frying pan that you use this morning for breakfast, iron.
08:37The moment the white dwarf star starts to fuse carbon and oxygen into iron, it's doomed.
08:47Suddenly, the white dwarf explodes.
09:08The nuclear explosion of a white dwarf include, among other things, huge amounts of iron.
09:13And in fact, type 1A supernovae are vital importance to populating the universe with the kind of elements that are important to us.
09:29Type 1A supernovas blast iron trillions of miles into space.
09:36That's where most of the iron in the cosmos comes from.
09:45But what about all the elements that are heavier than iron, like gold and silver?
09:50Where do they come from?
09:53The answer, again, is other stars, single stars, bigger stars.
10:12Supernovas make everything in the universe.
10:16Everything we see, all the material in planet Earth, was created inside a supernova.
10:24Even you and I are made from dying stars.
10:30Without supernovae, we wouldn't be here.
10:33Every atom in your body was once inside a star that exploded.
10:38And the atoms in your left hand may have come from a different star than the atoms in your right hand.
10:42You are literally stardust.
10:50Almost all of the iron in our solar system came from a double star supernova that exploded more than 5 billion years ago.
11:01From our planet's molten core, to our skyscrapers, to the hemoglobin in our blood,
11:13it's all made of iron from Type 1A supernovas.
11:20But the heavier elements in our world, like gold, silver and uranium, come from another type of supernova.
11:32A single star supernova.
11:38This is our sun.
11:41A single star has to weigh much more than our sun to go supernova.
11:48And there are some monster stars out there.
11:55Some are dozens of times heavier than our sun.
12:00And some are hundreds of times more massive.
12:08The heavier the star, the faster it burns.
12:13And when these massive stars begin to age and die, the nuclear reactions inside them speed up.
12:24Giant stars burn through their nuclear fuel very, very fast.
12:28Sort of the live fast, die young.
12:30The more mass a star has, the hotter it burns inside, the faster it burns through its fuel.
12:38Unlike double star supernovas, really massive single stars create lots of elements before they explode.
12:52Once they turn hydrogen into helium, helium into carbon, and carbon into oxygen, they don't collapse into white dwarf stars.
13:10Instead, giant stars keep on burning, building up layer after layer of new elements deep in their core.
13:23Big stars don't stop after they've burned helium to carbon and oxygen.
13:28They go ahead and burn carbon to still heavier elements, and then neon and oxygen to silicon.
13:34You get this nested Russian doll spherical layer cake kind of thing.
13:40These elements are the building blocks of the universe.
13:45But they're trapped inside the giant star.
13:50Somehow, they've got to get out.
13:54Studying exploding stars has taught us how the heavy elements of the universe came to be.
14:00They were formed by nuclear reactions inside stars.
14:04But if some of those stars were not to explode, then those elements would be locked up forever.
14:14The trigger that will release the elements in the single giant star is the same element that causes the type 1a supernova to blow up.
14:24Iron.
14:27Iron eats up all the energy of the star's nuclear fusion.
14:37Without the energy from nuclear fusion pushing out, gravity begins to crush down.
14:44The big star is doomed.
14:49The last moments of a star are really phenomenal.
14:53The star might last for 10 million years on the way to becoming a supernova, but the last little bit takes place very rapidly.
15:01Once you have an iron core and once it gets out of balance, it collapses in a thousandth of a second, a millisecond, from the size of the Earth down to the size of Manhattan.
15:12It's traveling about one-third of the speed of light as it crunches down.
15:21As the star becomes unstable, the massive power of gravity causes the core to collapse.
15:28This happens with such incredible power, even the atoms inside start to crush together.
15:43As it gets smaller and denser, the core builds up more and more energy.
15:49It's something with about one and a half times the mass of the sun that has collapsed to something that's only about 15 miles across.
16:01It's got incredible density.
16:03It's a thousand trillion times the density of water.
16:08The star explodes.
16:27The blast rips through the star's outer layers and in the process makes all the elements heavier than iron.
16:43Iron becomes cobalt.
16:46Cobalt becomes nickel, and on and on to gold, platinum, and uranium.
16:59The explosion is so brief, it only makes small amounts of these heavier elements, which is why they're so rare.
17:11The supernova blasts these new elements billions of miles into space.
17:17The only method we know, the only mechanism that we have found anywhere in the universe for creating new elements is in the death throes of a star called a supernova.
17:29It seems incredible that anything could survive a supernova explosion.
17:38We now know that some of the biggest bangs in the universe leave a corpse behind.
17:46And these are some of the strangest and most deadly objects ever discovered.
17:59When a giant star goes supernova and explodes, it's not always the end.
18:06Sometimes there's a corpse.
18:16What kind of corpse depends on the size of the star.
18:26Supernovas from stars more than eight times bigger than our sun leave behind a neutron star, and it's one of the strangest objects in the universe.
18:40These things you can almost think of as sort of the zombies of the stellar world.
18:44They're very dangerous, they're very weird, and stars make them all the time.
18:48They're all around us.
18:54As a giant star goes supernova, the core is crushed from the size of a planet to the size of a city.
19:05The pressure in the core is so intense, even the atoms inside it are crushed together.
19:15When the atoms are packed that tightly and there's no space left between them, the massive energy buildup means something's got to give.
19:34The core blasts off the outer layers of the star.
19:44All that remains is a super dense neutron star.
19:50A neutron star has the mass of a star crunched into a very small volume, and that means the density is incredibly high.
19:59Well, imagine taking the Empire State Building here behind me, crushing it into the size of a grain of sand.
20:05That's the density of the entire neutron star.
20:10If you had something that dense, if you dropped it, it would fall straight through the Earth, just like a hot knife through butter.
20:20A teaspoon of neutron star would weigh 100 million tons.
20:31Imagine something as heavy as a star, but only the size of New York City, and it's spinning.
20:40Some of them may be born rotating 1,000 times a second.
20:43I mean, think about it.
20:44Something one and a half times the mass of the sun going around 1,000 times a second.
20:51Some neutron stars spin so fast, they generate huge pulses of energy.
20:59Beams of radiation blasting out of the star's north and south poles.
21:06This neutron star is called a pulsar.
21:10There's one of these things in the center of the Crab Nebula, the place where there was a supernova explosion about 1,000 years ago.
21:18And it's one of the fastest spinning of these objects.
21:23This is the actual sound a pulsar makes, recorded by radio telescope.
21:32It will flash 30 times a second for millions of years.
21:47But pulsars aren't the strangest thing a supernova can leave behind.
21:55When stars 30 times bigger than our sun explode, they produce a type of neutron star called a magnetar.
22:12Magnetars are even weirder than pulsars and generate powerful magnetic fields.
22:20Now, in the most extreme case, the magnetic field can be 10 to the 15, you know, 100 trillion times the magnetic field of the Earth.
22:33It's so strong, it would suck the iron right out of your blood from thousands of miles away.
22:41But even pulsars and magnetars aren't the most dangerous objects a supernova can leave behind.
22:50When the core of a supermassive star collapses, it doesn't just crush atoms, it crushes space and time itself.
23:02That is when a supernova creates a black hole.
23:16When stars over 100 times heavier than our sun explode, they make a supernova explosion so big, scientists call them papernovas.
23:32And it was a hypernova that almost started World War III.
23:44In 1963, the U.S. and Soviet Union agreed to ban testing nuclear weapons.
23:59To keep tabs on the Russians, the U.S. launched spy satellites.
24:07When they heard this sound coming from deep space, they suspected the worst.
24:20The United States government launched the Vela satellite, looking for nuclear detonations.
24:31And then, looking in outer space, they saw these monster explosions take place.
24:37And the military thought, oh, my God, the Russians, the Russians are testing secret atomic weapons in space.
24:44But these weren't secret atomic bomb tests, and the Russians had nothing to do with them.
24:51They began to look at where this radiation came from. It came from all over the galaxy, beyond the galaxy.
24:57Now, there's no way the Russians could shoot explosions in outer space beyond the galaxy.
25:03And then, people began to realize that we were staring something new in the face.
25:10They were super-powerful explosions of high-energy radiation called gamma-ray bursts.
25:17The question was, where did they come from?
25:23The answer was exploding hypernovas.
25:29During a regular supernova explosion, gravity crushes a star's core into a neutron star.
25:44But during a hypernova explosion, the giant star is so much bigger that gravity crushes the core into something much stranger.
25:57A black hole.
26:02And the black hole immediately begins to devour the dying star around it.
26:09The rest of the star can't all go in that little bitty hole in the middle.
26:13It starts to swirl around, and it forms an accretion disk, which is feeding the black hole at about a million Earth masses a second.
26:20And so, as you might imagine, something dramatic is going to happen here.
26:27A million Earth masses a second is too much for the black hole to consume all at once.
26:38So it spits a lot of it back out at nearly the speed of light.
26:48This creates two beams of pure energy blasting their way out of the black hole.
26:56It takes it about eight seconds to bore through the star, keeping a very tight focus, and erupt from the surface.
27:03Now, if we're standing in the opening of this jet, we'll see a gamma-ray burst.
27:12The gamma-rays produced from the black hole tear through the outer layers of the star and into space.
27:19Gamma-ray bursts are the most violent event that we know of in the universe.
27:23A giant star blows itself to pieces and forms a black hole.
27:26It's incredibly spectacular.
27:28These gamma-ray bursts are so energetic, they light up the entire universe.
27:32Any point in the universe will eventually pick up this astounding radiation coming from a gamma-ray burst.
27:39Look at how energetic they are.
27:43They are the brightest things in the known universe.
27:48To put things in perspective, a typical supernova explosion is about what the sun will put out in its entire 10-billion-year lifetime.
27:56A gamma-ray burst viewed jet-on is 100 million times more luminous than a supernova.
28:04It's a great experience for brightness, for sure.
28:12They're not only bright, they're lethal.
28:20If a gamma-ray burst were to hit the Earth, it would destroy most of the atmosphere in seconds.
28:29A gamma-ray burster is like a rifle shot.
28:35And if you're in the line of sight, watch out.
28:40Once the radiation hits you, it'll bathe the entire surface of the Earth with nitric oxides, which will wipe out the ozone layer.
28:50Blistering radiation would hit plant life, hit algae.
28:54The whole food chain would collapse.
28:57If a gamma-ray burst was close enough, it would cause mass extinctions.
29:02Gamma-ray bursts turn out to be a lot more common than we thought they would be.
29:05So it's possible that some of these have even hit the Earth in the past.
29:08That's a pretty scary scenario. It may already have happened.
29:14The question is, if it happened before, could it happen again?
29:23A gamma-ray burster is basically a supernova on steroids.
29:27You need a giant star to die violently.
29:29Now, the nearest star to us that might do that is Eta Carinae.
29:32And it's a spectacular nebula.
29:34There's all kinds of material flying off this star. It's very unstable.
29:38It may already have exploded in a gamma-ray burst.
29:42But Eta Carinae may not be the only threat.
29:46There are other dying stars out there.
29:50Believe it or not, one of them is pointed in our direction.
29:55We are staring down the gun barrel of WR-104,
30:00two dying stars that will one day undergo the gamma-ray burst.
30:05Not a question of if, a question of when.
30:10That WR-104 may have our name on it.
30:14But the good news is we probably wouldn't know about it in advance.
30:17The rocket would hit us before we had a chance to do anything.
30:20So there's no sense worrying about it anyway.
30:29The truth is, we'll never know if a star is about to go hypernova and explode.
30:38Anyway, by the time we see it, it'll already be too late.
30:43In fact, we're already exposed to rays from dying stars every second of every day.
30:57When giant stars explode,
31:01they make the biggest bangs in the universe.
31:06But what gives them so much punch?
31:12Until recently, no one knew.
31:16Scientists, when they tried to simulate a supernova explosion in a computer,
31:20had a problem.
31:23They simply could not get enough energy out of the dying star
31:27to create a supernova explosion.
31:31They simply could not get enough energy out of the dying star to create a supernova.
31:36This was a calamity in astronomy.
31:48Computer models couldn't make the simulated stars blow up.
31:53To blow up a star, you need a lot of energy.
31:57To blow up a star, you need a lot of energy.
32:01The trouble was, astronomers couldn't find it.
32:05The visible radiation that you see
32:09is a tiny fraction of the total energy emitted.
32:13Even the energy of motion of the expanding gases
32:17is only 1% of the total energy.
32:21Where was the missing 99% of the energy from the explosion?
32:25The only way scientists could get their simulations
32:29to match the real thing was to add in a mysterious particle
32:33called the neutrino.
32:37Without it, their numbers didn't add up.
32:41That was the easy bit.
32:45Their next step was to prove supernovas really do produce neutrinos.
32:51In 1987, they got lucky.
32:59168,000 years ago,
33:03a supernova exploded in a nearby galaxy
33:07called the Large Magellanic Cloud.
33:11When scientists saw the light from the blast,
33:15they called it Supernova 1987.
33:21Supernova 1987A is really important in the study of supernovae
33:25because it's the first one since the invention of the telescope.
33:29It's the one that we've been able to study
33:33right from the time of explosion through now
33:37using all the instruments that we've developed.
33:41One of those instruments was a giant neutrino detector
33:45buried deep underground.
33:49We looked at the detectors, and we said,
33:53aha, that's the proof.
33:57The discovery of neutrinos from Supernova 1987A was a tremendous thing
34:01because for many years, people had been saying
34:05that's where 99% of the energy goes, but no one had ever seen it.
34:09This is now the smoking gun that we can now prove
34:13that neutrinos carry the energy of a supernova,
34:17and that's what it is.
34:21Neutrinos are trillions of times smaller than atoms.
34:29They're created by all sorts of nuclear reactions,
34:33from nuclear power plants, bombs,
34:37to exploding stars.
34:41If you had neutrino vision, you'd see them everywhere.
34:47Neutrinos are ghost-like particles.
34:55Literally trillions of them are going through my body
34:59even as we speak.
35:03In fact, neutrinos come from the bottom of the floor right through the Earth
35:07and even hit me right through my legs.
35:11Pretty strange.
35:15But where do they get all their energy?
35:23When a core crushes down just before a supernova explosion,
35:27the atoms inside it are broken up.
35:35The core gets so hot, it turns this atomic debris into blazing neutrinos.
35:45We think that supernovae produce a stupendous sum of neutrinos
35:49when the core collapses to a neutron star.
35:53For about ten seconds, that core shines with a neutrino luminosity
35:57that is greater than all of the energy being produced
36:01in the rest of the universe at that time.
36:05In other words, it's really bright.
36:09But gravity can't hold these neutrinos in the core.
36:13They burst free in a blinding flash of light
36:17that rips the dying star apart.
36:25The discovery of neutrinos transformed the science of supernovas.
36:31But supernovas were about to reveal
36:35the most mysterious force of all,
36:39creating the destiny of the universe.
36:51Supernova explosions are so bright,
36:55we can see them across the entire universe.
36:59This has helped astronomers unlock
37:03one of the deepest mysteries of the cosmos.
37:09The universe came to life in the Big Bang 14 billion years ago.
37:19It expanded from a tiny ball of energy, smaller than an atom,
37:23to a universe billions and billions of light-years across.
37:29And it's still expanding.
37:33I've often wondered how far future people will even know the Big Bang happened,
37:37because we know the Big Bang happened
37:41from watching all the galaxies fly away from us.
37:45Someday, the galaxies will be so far away from each other,
37:49it will be impossible to see anything else in the sky.
37:53Scientists used to think the expanding universe was slowing down,
37:57but there was no way to prove it.
38:01Until they found double-star supernovas, type Ia's.
38:09They always explode when the white dwarf star
38:13reaches exactly 1.4 times the mass of our sun.
38:23And their explosions always release
38:27exactly the same amount of light.
38:31They are the perfect markers
38:35to measure distance in space.
38:39Type Ia supernovae, when we know how bright they are
38:43and how bright they look, we can tell the distance.
38:47Because the farther away they are, the less bright they'll look in the telescope.
38:51And that has allowed us to accurately measure distances
38:55not just to nearby galaxies, but to galaxies at the other end of the visible universe.
38:59Billions of light-years, and that has allowed us
39:03to make incredible discoveries.
39:07Astronomers thought they had found a way to prove
39:11the expansion rate of the universe was slowing down.
39:15What they got was a big surprise.
39:19In 1998, astronomers made a remarkable and unexpected discovery.
39:23It was recognized that the universe, which should be slowing down
39:27because gravity, after all, is attractive, and the mass of objects
39:31should cause the expansion of the universe to slow down,
39:35that the expansion is speeding up. It's accelerating.
39:41The constant light from type Ia supernovas
39:45completely changed the way astronomers understand the universe.
39:49Every science textbook on the Earth
39:53says that the universe is expanding and slowing down.
39:57Wrong. We now have to rewrite all the science textbooks on the planet Earth.
40:07But astronomers still didn't know why the universe
40:11is expanding faster and faster.
40:15They began to think it's some kind of unknown energy.
40:21They called it dark energy, but it's difficult to prove
40:25because it can't be seen or touched or detected.
40:31We really don't have a very good clue as to the physical nature
40:35and origin of dark energy.
40:39It's perhaps the number one observationally motivated problem
40:43in all of physics right now, the nature of the dark energy.
40:57From dark energy, the black holes, supernovas have revealed
41:01some of the most profound mysteries of the universe.
41:05These exploding stars
41:09give us the building blocks of the universe
41:13and show us how it's all made.
41:17It's hard to imagine, but the atoms in our bodies today
41:21were made by a supernova billions of years ago.
41:29The Bible says from dust to dust.
41:33Astronomers say from stardust to stardust.
41:37So supernovae are the key link in this cycle of life.
41:43People think of space as being something very distant and very remote.
41:47It's light years away, hugely distant from us.
41:51That's completely wrong. Supernovae are right here.
41:55We are their children. They made us, literally put us together.
41:59Without our stuff, without the supernovas, we could not exist.
42:03So when we walk around at night and we look up at the night sky
42:07and we see the stars and we feel somehow a part of them,
42:11the truth is, we are. They are our parents.
42:23Some scientists believe the age of supernovas
42:27could be ending. Smaller, slower burning stars
42:31like our sun will become more common
42:35and giant stars become more rare.
42:43Supernovas have given us galaxies, solar systems,
42:47stars and planets.
42:51They made us and everything we see.
42:55They are where destruction and creation meet.
42:59The destiny of the universe lies in the ashes
43:03of dying stars.