How the Universe Works - S01E04 - Stars
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00:00Stars. They're big. They're hot. And they are everywhere. Stars rule the universe.
00:12Our destiny is linked to the destiny of stars. Born in violence, dying in epic explosions,
00:24they fill the universe with stardust, the building blocks of life. Every atom in your
00:31body was produced inside the fiery core of a star. Stars are what make our universe work.
00:39All life begins here. The night sky is packed with stars.
01:08On a clear night in the country, if you're lucky, you can see maybe 3,000 stars. But
01:12that's just the tip of a vast cosmic iceberg. In our galaxy alone, there are over 100 billion
01:19stars. And in fact, there are over 100 billion galaxies in the observable universe. There
01:24are more stars than there are specks of sand on Earth.
01:31Every star is powerful, creating the basic matter for everything in the universe, including
01:40us. Most are so far away, we know little about them. But there is one star that's really
02:00close. And virtually everything we know about stars, we've learned from that neighbor.
02:06The sunlight from our sun that bathes us and warms us every day is nothing but starlight,
02:12because our sun is nothing but a star like all the rest.
02:18Seen from Earth, our sun is a blinding ball of light. But take away the glare, and one
02:26of the most powerful objects in the universe appears in our own backyard. It's a ball of
02:33superheated gas that's been lighting our solar system for 4.6 billion years and dominates
02:41all life on Earth.
02:44The sun is 93 million miles away. And that means, in actuality, it's immense. You could
02:50fit a million Earths inside the sun.
02:59It's nearly a million miles in diameter, yet our sun is tiny compared to the really big
03:04stars out there. Eta Carinae, over 5 million times larger than our sun. Betelgeuse, 300
03:23times larger than Eta Carinae. If it was our sun, it would reach as far out as Jupiter.
03:31And then there's this monster, VY Conus Majoris, the largest star ever discovered, a billion
03:41times bigger than our sun.
03:50Stars burn in different colors, from red to yellow to blue. Some live alone. Others in
04:00pairs, orbiting each other. And coming together in huge galaxies, entire cities made up of
04:12billions of stars.
04:24Each star is a one-of-a-kind. But they all start life in the same way, as clouds of dust
04:33and gas called nebulas.
04:42Many billions of miles across, they drift through space, forming spectacular shapes.
04:51The Flame Nebula.
04:57The Horsehead Nebula.
05:02The Orion Nebula.
05:04Each nebula is a star nursery where millions of new stars are being born.
05:16But this birth is hidden from view.
05:21Some of the more dramatic parts of a nebula are not the beautiful, glowing gas that you
05:25see, but the dark parts. The dark parts have areas of dense gas and dust, and that's where
05:31the real action is happening in terms of star formation.
05:37The dust clouds are so thick, regular telescopes can't see inside.
05:44There's nothing more important to us than stars. But for a long time, the way they formed
05:48was a complete mystery. We couldn't observe them. Imagine that. We could not see the first
05:53moments of a star at all.
05:56Until 2004, when NASA launched the Spitzer Space Telescope.
06:00And liftoff, seeking hidden secrets in the evolution of our universe.
06:25Spitzer is an infrared telescope. It only sees heat.
06:32Heat passes through the thick dust of the nebulas, allowing Spitzer to see new stars
06:38coming to life inside.
06:43These remarkable pictures capture the earliest moments in a star's life, as pockets of hydrogen
06:49gas begin to heat up.
06:53Any little bit of gas and dust is glowing. Areas that were entirely dark now became bright.
07:02We can actually see the very earliest parts of star formation.
07:12All you need to make a star is hydrogen, gravity, and time.
07:17Gravity pulls the dust and gas into a giant, swirling vortex.
07:24Gravity brings matter together. And when you bring matter together, and you squeeze things
07:29into smaller spaces, they necessarily heat up. It's a simple law of chemistry. You compress
07:34something, you drive the temperature up.
07:38Over hundreds of thousands of years, the cloud gets thicker and forms a giant, spinning disc
07:45bigger than our entire solar system. At its center, gravity crushes the gas into a super-dense,
07:53super-hot ball. Pressure builds until huge jets of gas burst out from the center.
08:03That really shows you how violent a process star formation is. These jets are many light
08:13years across. Something is literally accelerating material very fast across unimaginable distances.
08:24Gravity keeps the pressure on, sucking in gas and dust particles that smash into each
08:30other, generating more and more heat.
08:38Over the next half a million years, the young star gets smaller, brighter, and hotter. Temperatures
08:45at its core reach 15 million degrees.
08:53Only at that mind-boggling temperature can atoms of gas begin to fuse together, releasing
08:59massive amounts of energy.
09:20Just like that, a star is born.
09:30Stars will shine for millions, even billions, or perhaps even trillions of years.
09:59Stars produce massive amounts of heat and light over billions of years.
10:11But that takes fuel, and lots of it. Until the early 20th century, no one had any idea what this fuel was.
10:24The greatest problem facing physics at the turn of the last century was what drives the energy of stars?
10:31All you had to do was look outside and realize there was a huge gaping hole in our understanding.
10:37To solve the secret of the stars, we needed a new engine. We needed a fabulous source
10:44of energy that could drive a star for billions of years at a time.
10:51And it took a genius to discover it, Albert Einstein.
10:58His theories proved that stars could tap into the energy inside atoms.
11:08The secret of the stars is Einstein's equation E equals mc squared. In some sense, matter,
11:15which makes up our body, is concentrated energy, condensed energy, energy that has
11:22condensed into the atoms that make up our universe.
11:30Einstein showed that it's possible to release this energy by smashing atoms together.
11:38It's called fusion, the same force that powers stars.
11:45It's astonishing to realize that the physics of the very small subatomic particle physics
11:51determines the structure and nature of stars.
11:56From Einstein's theories, we learned how to release the energy inside an atom.
12:07Now science is trying to simulate a star's energy source to control the power of fusion
12:14in a lab.
12:25Inside this laboratory near Oxford, England, there's an 80,000-pound machine. Every day,
12:31Andy Kirk and his team transform it into a star on Earth.
12:38This machine is called a tokamak. It's effectively a large magnetic bottle, a cage to hold a
12:46very hot plasma. We're able to recreate the conditions within a star.
12:54Inside the tokamak, hydrogen atoms naturally repel each other.
13:02To smash hydrogen atoms together, the tokamak heats them to more than 300 million degrees.
13:15At these temperatures, the energized hydrogen atoms are moving so fast, they can't avoid
13:20smashing into each other.
13:22If you heat it up, heat is motion, and the motion of hot particles will change.
13:31It will be enough to overcome the repulsive force.
13:51When everything goes right, the result is the single best power plant in the universe,
13:58nuclear fusion.
14:10Traveling at 1,000 miles a second, the hydrogen atoms smash into each other and fuse,
14:20creating a new element, helium,
14:26a small amount of pure energy.
14:33The hydrogen gas weighs slightly more than the helium. You lost mass in the process of
14:39burning. That mass that you lost, the missing mass, turns into energy.
14:47The tokamak can only maintain fusion for a fraction of a second.
14:55But inside a real star, fusion continues for billions of years.
15:03The reason is simple, size.
15:08The engine which drives a star is gravity. That's why stars are big. Stars are huge.
15:14You need that amount of gravity in order to compress the star to create fantastic amounts
15:20of heat sufficient to ignite nuclear fusion.
15:30That is the secret of the stars. That's why stars shine.
15:38Fusion at the core of a star generates the explosive force of a billion nuclear bombs
15:45every second.
15:48A star is a gigantic hydrogen bomb. So why doesn't it simply blow apart?
15:53It's because gravity is compressing the outer layers of the star.
16:04Gravity and fusion lock horns in an epic battle.
16:09We have this constant tension between gravity, which wants to crush a star to smithereens,
16:14and also the energy released by the fusion process, which wants to blow the star apart.
16:20And that tension, that balancing act, creates a star.
16:26This power struggle plays out over the entire life of a star.
16:31Two awesome forces of nature in a dynamic standoff.
16:36As that battle rages, the star blasts out light and heat,
16:40but also something far more destructive.
16:53Each beam of starlight makes an epic journey.
17:00Light travels at 670 million miles an hour.
17:04A beam of light could travel around the Earth seven times in one second.
17:09Nothing in the universe moves faster.
17:13Yet most stars are so far away, their light takes hundreds, thousands, millions,
17:19even billions of years to reach us.
17:23So when the Hubble Space Telescope looks into the far corners of our universe,
17:28it sees light that's been traveling for billions of years.
17:34The light we see today from Eta Carinae left that star
17:39when our ancestors first farmed the land 8,000 years ago.
17:45Light from Betelgeuse has been traveling since Columbus discovered America 500 years ago.
17:53Even light from our own sun takes eight minutes to reach us.
18:04But even before light starts its journey through space,
18:08it's already been traveling for thousands of years.
18:12When the sun fuses hydrogen into helium in its core,
18:15it creates a photon of light, a particle of light.
18:20That new ray of light has a long way to go just to reach the star's surface.
18:26There's a whole star in its way, and so when the photon is created,
18:31it doesn't get very far before it immediately slams into another atom,
18:35another proton, another neutron, something.
18:38It gets absorbed and then shot off in another direction.
18:41And so it's sort of randomly moving around inside of the sun,
18:45and it has to work its way out.
18:49For the photons, it's a wild ride,
18:52smashing into atoms of gas billions of times
18:56as they struggle to escape from inside the star.
19:00What's funny about this whole process
19:02is that it takes the photon thousands and thousands of years
19:06to get from the core of the sun to the surface.
19:09And yet once it hits the surface,
19:11it's only an eight-minute trip from there to here.
19:16Photons are the source of light and heat,
19:19but they also cause something far more destructive, the solar wind.
19:26As they reach the surface,
19:28photons heat up the outer layers of the sun,
19:34sending it hurtling around the star,
19:37creating extreme turbulence and intense shock waves.
19:43It's so violent, we can actually hear it.
19:48Picked up by the orbiting SOHO satellite,
19:51this is the sound of the sun.
20:00The speeding gases also generate powerful magnetic fields.
20:05As the star rotates, the fields clash and burst through the surface.
20:14Giant magnetic loops erupt into space.
20:20Some are so large, the Earth could pass right through them
20:24with thousands of miles to spare.
20:28They are spectacular, and they are deadly,
20:31blasting a stream of electrical particles deep into space.
20:39This is the solar wind.
20:43It can damage spaceships and satellites,
20:47even put astronauts' lives in jeopardy.
20:52To discover how the magnetic loops trigger the solar wind,
20:56a team of scientists at Caltech recreate the surface of a star,
21:01right here on Earth.
21:05It's very exciting to be able to create in a laboratory
21:09the same sort of physics that are on the solar surface.
21:13We can't go there, we can't even send probes there,
21:16but we can try to study what's happening there.
21:24An airless chamber simulates the vacuum of space.
21:29An enormous electric current produces a pair of man-made magnetic loops.
21:37The main difference between the plasma loops we make in the lab
21:41and the ones on the surface of the sun is just their size.
21:44The ones we make in lab are, you know, about this big,
21:47and the ones on the surface of the sun can be many times the size of the Earth.
21:53Their experiment reveals that when magnetic loops clash in the lab,
21:58they trigger a massive burst of energy.
22:03When giant loops collide on the surface of a star,
22:07the energy released sends temperatures soaring
22:11from 10,000 to 10 million degrees.
22:16That extreme heat triggers the solar wind,
22:20and when it hits the surface of the star,
22:23the energy released sends temperatures soaring from 10,000 to 10 million degrees.
22:29That extreme heat triggers the solar wind,
22:32sending millions of tons of particles streaming out into space.
22:46The bigger the star, the more deadly the wind.
22:52If we were orbiting a star like Eta Carinae at the same distance,
22:56it would be hell on Earth, quite literally.
23:00The amount of energy blasting down on the Earth would strip away our atmosphere,
23:04boil our oceans, melt the surface.
23:10Understanding how stars work could help us protect ourselves
23:15by predicting their most destructive forces.
23:19But there's nothing we can do to protect ourselves when a star dies.
23:27In its final moments, it annihilates everything around it.
23:47From the moment of its birth, every star is destined to die.
23:53Its fuel will run out.
23:59Then gravity will win the battle with fusion,
24:02triggering a chain of events that will destroy the star.
24:17Our sun is no exception.
24:21Every second, it burns through 600 million tons of the hydrogen fuel in its core.
24:29At that rate, the hydrogen will run out in about 7 billion years.
24:41As the hydrogen gets used up, it slows down the fusion at the star's core.
24:46This gives gravity the edge.
24:49With less fusion pushing outward, gravity crushes the star in on itself.
24:55But fusion fights back, heating the star's outer layers.
25:02When you heat up a gas, it expands.
25:04And so the sun will actually expand up.
25:07Instead of being a million miles across like it is now,
25:10it'll swell up until it's about 100 million miles across.
25:16Our sun will become a red giant.
25:21Imagine a sunrise, 7 billion A.D.
25:27It's not just a little yellow disc coming up all cheerful and nice.
25:31What you would see is a huge, swollen, bloated red disc
25:35slowly reaching up over the horizon.
25:37And when the sun is fully up in the sky, it's blasting down heat on the Earth.
25:42It would be like sticking your head in an oven set to boil.
25:52Temperatures here on Earth will reach thousands of degrees.
25:58The oceans will boil, the mountains will melt,
26:01and we'll have the last nice day on the planet Earth.
26:07Then the bloated star will engulf the Earth.
26:23But the giant red star is self-destructing.
26:28Its core becomes dangerously unstable.
26:36With no hydrogen left to fuel it,
26:39the star begins burning helium and fusing it into carbon.
26:43The star is now destroying itself from the inside out,
26:47blasting violent surges of energy from its core to its surface.
26:55These energy waves blow away the star's outer layers.
27:07Slowly, it disintegrates.
27:16The star is dead.
27:20All that remains is an intensely hot, dense core.
27:25The red giant has become a white dwarf.
27:31By the time a star reaches the white dwarf stage,
27:35the fusion process has stopped.
27:38The engine has finally come to rest.
27:43Our sun will end its life as a white dwarf,
27:46no larger than the Earth, but a million times denser.
27:51A white dwarf is a pretty amazing object.
27:54It's incredibly dense.
27:56If you could take a sugar cube-sized chunk of white dwarf
27:59and put it on the surface of the Earth,
28:01it would be so dense it would fall right through the ground.
28:08At the heart of a white dwarf, astronomers believe,
28:11there's a giant crystal of pure carbon,
28:16a cosmic diamond thousands of miles across.
28:24The idea that the sun will become this sort of cool, dark lump
28:28of cinder material is kind of sad,
28:31but that really will be sort of a trillion, trillion, trillion carat diamond.
28:36Think of that, a diamond in the sky.
28:45But stars can create something much more precious than a massive diamond.
28:54When stars much bigger than our sun die,
28:57their death is much more violent.
29:00But in dying, they create the building blocks of life.
29:14Giant stars live fast, burn bright, and die hard.
29:21But from their destruction comes life.
29:26The death of massive stars creates the building blocks of the universe,
29:31the seeds of life itself.
29:39Less than 600 light years from Earth,
29:41the monster star Betelgeuse is near death.
29:45Well, in space years.
29:48It's younger than our sun, millions, not billions of years old.
29:52But the fusion at its core is far more intense.
29:57Betelgeuse is a different beast from the sun entirely.
30:00It's a red supergiant.
30:02And the reason is because Betelgeuse is more massive.
30:06It has 20 times the mass of the sun.
30:08And that means what's going on in its core
30:11is very different than what's going on in the sun's.
30:17Massive stars generate pressures and temperatures
30:21greater than anywhere else in the universe.
30:32The gravity of Betelgeuse is so powerful
30:35it can smash together bigger and bigger atoms.
30:43The core of a massive star is a kind of factory
30:46manufacturing heavier and heavier elements.
30:52Which is what also leads to the star's destruction.
30:58Once it makes the element iron, the star is doomed.
31:05In the world of science fiction, there are many ideas
31:07about what a star killer machine might be like.
31:10Strangely enough, it's as run-of-the-mill as something as iron.
31:13To a star, iron is the most dangerous element in the universe.
31:17It's poison.
31:22Iron absorbs energy.
31:26From the moment a massive star creates iron,
31:29it has only seconds to live.
31:34The star is trying to dump energy into that iron ball
31:37and trying to make it fuse, but it can't.
31:40And so that ball is robbing the star of energy.
31:43And it's that energy that is supporting the star itself.
31:46So as soon as that iron starts to be created in the core,
31:50the star has written its own death sentence.
31:53The battle between gravity, trying to crush the star,
31:56and fusion, trying to blow it apart, is over.
32:00With iron, fusion hits a dead end.
32:03Gravity always wins.
32:10The iron core collapses.
32:12The outer layers of the star slam down into it.
32:14And a huge explosion is generated.
32:21It's the single most violent event in the universe, a supernova.
32:28In just a few seconds, supernovas create more energy than our sun ever will.
32:37Within a couple seconds after beginning to make iron,
32:40a star explodes in a supernova.
32:42So think about that when you're holding one of your iron frying pans.
32:45The iron killed a star in just a few seconds.
32:48Dangerous stuff.
32:56Telescopes around the world scan the skies for supernovas.
33:02In 1987, a brilliant light appeared in a nearby galaxy,
33:06170,000 light years away.
33:12These pictures record the events following the death of a massive star
33:17as a fireball, trillions of miles wide, hurtles out into space.
33:30But there's no record of the actual moment of death
33:33when the star first ripped itself apart.
33:48The only way to know what happens inside a massive star when it explodes
33:53is to make our own supernova.
33:57What's amazing when these stars explode is that they almost turn inside out.
34:03Here in this lab in Rochester, New York,
34:06scientists are making a supernova with a giant laser.
34:13Telescopes can't see inside the dying star.
34:16With this laser, we can detect the processes that occur as the star explodes.
34:21Working with these tools is the most exciting thing I can imagine doing.
34:28This massive machine amplifies the power of a single laser beam
34:32a thousand million million times.
34:35That's enough power to supply 30 cities the size of Detroit.
34:40And all that energy will be directed toward an area the size of a pinhead.
34:46This tiny target has a star's core.
34:50The laser simulates the most violent explosion in the universe.
34:55This would not be a safe place to be when the laser was fired
34:58if a human was struck by all these laser beams
35:01and it would drill a hole right through them.
35:05Now I'm going to close access in the laser bay.
35:07The door is locked.
35:11Preparation is complete.
35:14Five, four, three, two, one.
35:26The target is vaporized by the laser.
35:32The explosion lasts just a hundred thousandth of a second,
35:36but a high-speed camera captures the shockwave expanding outwards.
35:41Some of the inner material comes out
35:44and trades places with the outer material
35:46and that turning inside out is just what happens in a stellar explosion.
35:55Material from deep inside a star's core
35:58surfs the shockwave out into space.
36:03In the extreme heat and turmoil of the explosion,
36:06heavier elements are forged.
36:12Among them, gold, silver and platinum.
36:16And because there's so little time for the elements to form,
36:19they're the rarest and most valuable in the universe.
36:24Silver, gold, everything else are created by the explosion of the star,
36:28by the immense energy released, and that's how they come to us.
36:36But even after the universe's most violent explosion,
36:39there's something left behind.
36:42We scientists used to believe that after a supernova explosion,
36:46a star would literally blow itself to bits and there'd be nothing left.
36:51Well, we were wrong.
36:52There's a corpse, a corpse of a supernova explosion,
36:56some of the most exotic matter known to science,
37:00called a neutron star.
37:02Solid nucleonic matter,
37:04the most fantastic state of matter in the universe.
37:10The super-dense core is now a neutron star.
37:18It's around 20 miles across and unbelievably heavy.
37:25It's incredibly dense.
37:27Just a cubic centimeter, just the size of a sugar cube,
37:30of neutron star material would weigh as much as all the cars
37:34in the United States of America combined.
37:40The dying star doesn't just leave the corpse of a neutron star.
37:44It blasts the new elements far out into space.
37:50These clouds contain the building blocks of the universe.
37:54Everything we know and love is built from this stardust.
37:59Only a supernova has enough energy to fuse these elements
38:04which are so essential for life.
38:07Without supernovae, there's no life.
38:10There's no you and there's no me.
38:13When massive stars die,
38:16they seed the universe with stardust.
38:21Full of elements like hydrogen,
38:24carbon, oxygen,
38:27silicon, and iron.
38:34The raw materials of a neutron star
38:37can be used to build a supernova.
38:40But it's not enough to build a supernova.
38:44It's not enough to build a neutron star.
38:48The raw materials to build new stars,
38:51solar systems, planets,
38:54and, of course, us.
38:59Everything we see around us
39:02once blasted out from the core of a star.
39:06You may wonder what stardust is.
39:09Well, your stardust.
39:11Because every atom in your body
39:14is inside the fiery core of a star.
39:17The atoms in your left hand
39:20may come from a different star from the atoms in your right hand.
39:23But you are literally a star child.
39:32Long dead stars provided the stardust
39:35to create our solar system,
39:38the planets, and everything on them.
39:45So you're made of carbon. You're made of oxygen.
39:48There's iron in your blood.
39:50All of those things had to be generated inside the core of a star.
39:53There's no other way to get them.
39:55So when you think about star stuff, look around you.
39:58Everything that you're made of, everything the world around you is made of
40:01had to come from the belly of a star that blew up a long time ago.
40:08Even the atoms in our own sun are recycled.
40:12They're third or fourth generation,
40:15leftover debris shot into space by dying stars a long time ago.
40:22Our sun is our stepmother.
40:25Our true mother died in a supernova explosion
40:28to give birth to the elements which made up our body.
40:32But how come the poets and the songwriters,
40:35how come they don't write poems to our true mother?
40:38Or perhaps they don't understand physics and the laws of stellar evolution.
40:45We live in an age of stars.
40:48But it will come to an end.
40:51There's only so much hydrogen in the universe.
40:56Trillions of years from now, it'll all be used up.
41:01And when there's no hydrogen left, there'll be no new stars.
41:06We live in a very brief period in the history of the universe
41:11when we still have stars illuminating the sky,
41:14stars creating life as we know it.
41:17But it's not going to last forever.
41:20Sooner or later, the stars will begin to blink out.
41:24First, the massive stars will burn out.
41:27Then, mid-sized stars, like our sun,
41:30leaving only the smallest.
41:33Trillions of years later, they too will fade away.
41:39Slowly, inexorably, the universe will get colder and darker
41:45until the last star burns out
41:48and the universe becomes dark once again.
41:53The age of stars will be over.
41:57Honestly, the future of the universe looks kind of grim,
42:00but you can take something positive out of that.
42:02This is the best time to be alive.
42:04This is the time where life can flourish, stars can form.
42:07We are in the golden age of the universe right now.
42:12We live in a season for life in the universe, if you will,
42:16that lasts for a few billion years.
42:18And that makes me at least appreciate the way things are right now,
42:22because they weren't always that way, and they won't always be.
42:27We live in the stage where stars glow and illuminate the night sky
42:31when stars create life as we know it.
42:34We live in the best of all stages of the universe.
42:43For now, stars will continue to shape our universe,
42:47generating the building blocks of new worlds,
42:51creating new stars, and filling the darkness with light.
43:01NASA Jet Propulsion Laboratory, California Institute of Technology