The universe's stars are dying off faster than new ones are being born. Using the latest technology, experts investigate the secrets of the last stars of the cosmos and what this stellar apocalypse means for life on Earth.
Thanks for watching. Follow for more videos.
#cosmosspacescience
#howtheuniverseworks
#season8
#episode4
#cosmology
#astronomy
#spacescience
#space
#nasa
#spacetime
#deathofuniverse
#deathoflaststar
#darkuniverse
#universewithoutstars
#stellarapocalypse
#deathofstar
Thanks for watching. Follow for more videos.
#cosmosspacescience
#howtheuniverseworks
#season8
#episode4
#cosmology
#astronomy
#spacescience
#space
#nasa
#spacetime
#deathofuniverse
#deathoflaststar
#darkuniverse
#universewithoutstars
#stellarapocalypse
#deathofstar
Category
📚
LearningTranscript
00:00Imagine a universe with no stars.
00:09A dark, endless night.
00:13This is not some sci-fi nightmare.
00:18This is our future.
00:21There will definitely be a point in the future when you look up, you will no longer be able to see stars.
00:26Things really will get darker and darker until there will be almost no memory of light left.
00:33For billions of years, stars brought life to the universe.
00:39The fact that you exist at all is because of stars.
00:45Now, they're dying out in a star apocalypse.
00:50The effect could be tremendous. It can permeate throughout the universe.
00:56What's causing the die-off?
00:58And what happens to life when the lights go out?
01:04Eventually, the whole entire universe starts to get a little bit weird.
01:08For over four and a half billion years, the sun has bathed our home planet with light.
01:29Its bright, stable glow helps life flourish.
01:36But hidden in the night sky, other planetary systems haven't been so lucky.
01:43Hanging right above your head every night, we see up there these dead corpses of stars.
01:49400 light years from Earth lies a system called SDSS-J1228.
01:57A disk of debris orbits the faintly glowing leftovers of a dead star.
02:04J1228 is a dead star.
02:06It is the core of a star that had aged, blown off its outer layers, revealed the core,
02:12which is about the size of the Earth, but has about half the mass of the star in it.
02:16And we call these white dwarfs.
02:25May, 2018.
02:28Astronomers investigated J1228 using the world's largest optical telescope,
02:34the Grand Telescopio Canarias.
02:36They discovered what appears to be a ball of iron orbiting the white dwarf.
02:44The lump of metal, less than 400 miles across, could be the exposed core of a destroyed planet.
02:53It's a clue to this system's past.
02:57It's always a little poignant when you see evidence of a planet around a dead star.
03:01You know, you think back when that star was shining, and could there have been life in that solar system?
03:06The J1228 system is a cosmic graveyard.
03:11It might look different than our solar system, but this is our future.
03:18This discovery of a dead planet orbiting a dead star is like looking into a crystal ball.
03:24And is it the future of our own solar system?
03:28Yep.
03:29For a glimpse into your future, you know, all you need to do is look up.
03:37Just like J1228, our sun will die.
03:42Killing off Earth in the process.
03:46This terrifying fate will play out across the galaxy in a star apocalypse.
03:52Our sun is a fairly common type of star in the Milky Way.
03:57And so other stars in the Milky Way will undergo the same sort of fate as the sun, and will end up as white dwarfs.
04:03And so any other planets out there orbiting sun-like stars will undergo a similar fate.
04:11Once the stars like our sun have died out, what's going to happen?
04:14Could life still survive around white dwarfs?
04:16To understand the fate of sun-like stars, we have to look inside them.
04:23Buried within are clues to how they live and why they die.
04:28The core, the very center, that's where the action is.
04:31That's where the star is fusing light elements into heavier elements.
04:36And that works like a hydrogen bomb.
04:38It's the same thing.
04:40If you compress hydrogen enough, it gets very hot.
04:43And the pressure gets very high.
04:45And it fuses into helium and generates energy, heat.
04:49And that's what's happening in the core of every star.
04:51Because of their enormous mass, stars have huge amounts of gravity.
04:57This gravity pushes inwards, trying to collapse the star.
05:02But fusion energy from the core stops that from happening.
05:08It's really this sort of very balanced dance between gravity pushing in, fusion energy pushing out.
05:14You can think of a star as losing energy continuously to the outside world.
05:21And gravity is saying, yes, I'm going to take over.
05:23But no, the nuclear reactions inside a star replenish the energy that's lost
05:30and keep the star hot and pressurized inside so that the pressure-gravity balance can be maintained.
05:38This balance keeps sun-like stars alive for up to 10 billion years until the star's gas tank runs dry.
05:51It's going to run out of fuel.
05:53And when that happens, it's going to die.
05:56But what is that going to look like?
05:57How is this going to happen?
06:01100 million years ago, things in the J-1228 system started to get ugly.
06:08First, the star grew large.
06:12Really large.
06:14Once the center starts fusing heavier elements, the outside will swell into what will eventually be a red giant star.
06:23J-1228 transformed into a red giant.
06:28Its outer layers blew off, extending out over 40 million miles.
06:32When stars like our sun die, it's not a quiet affair.
06:38It's very violent and ugly and messy.
06:41They turn into red giants and they turn themselves inside out and vomit all over the solar system.
06:47When J-1228 swelled into a red giant, nearby planets were stuck in a kill zone.
06:58The dying star engulfed them, or fried them with temperatures of over 1,200 degrees Fahrenheit.
07:06Atnospheres disappeared.
07:08Oceans boiled away.
07:10But one planet survived J-1228's death throes.
07:15Here's a case where a planet survived, in some sense, the death of its own star and is still hanging around.
07:23Still hanging on, hoping for something new.
07:26The red giant's expanding outer layers separated from the star's core.
07:34With no active fusion, the core collapsed into a white dwarf.
07:41The white dwarf's dense gravity then went to work on the one surviving planet.
07:47A planet that might have been orbiting the normal star can gradually spiral in toward the white dwarf.
07:56And then eventually, the gravity of the white dwarf pulls on the near side of the planet more than on the far side.
08:02And that tears it apart.
08:04What we're seeing here is a dead star dining on its own solar system.
08:12That's what is in the future for the sun.
08:17J-1228 feasted on the remains of its rocky worlds, leaving behind a disk of debris and the planetary core.
08:29It's a glimpse of Earth's future.
08:33What happened here around this white dwarf is going to happen to Earth.
08:37It's going to be stripped of its atmosphere, its crust, and its mantle.
08:42And the only thing that will remain will be the core.
08:44Fried and ripped apart by a dying star.
08:49Not a good way to go.
08:52Fortunately, for life on Earth, our own sun isn't dying just yet.
08:58The sun is middle-aged.
09:00It's four and a half billion years old, and it's going to go on for another five or six billion years.
09:05We've got a little bit of time before our sun pukes all over the solar system.
09:09Our home planet may be safe for now, but systems like J-1228 show us that sun-like stars are destined to die.
09:20Killing off any life orbiting them.
09:24But sun-like stars aren't the only stars dying across the cosmos.
09:30There are others out there, and they're all doomed.
09:34There's a wonderful rainbow of stars out there of all different shapes, all different sizes, and all different colors.
09:43We're talking down to, you know, fractions of the mass of the sun, up to hundreds of times the mass of the sun.
09:50When it comes to the star apocalypse, size matters.
09:54The bigger and brighter the star, the faster it dies.
09:57Our universe is a vast expanse of death and destruction.
10:21All of the stars are destined to die, but not all at once.
10:31There's not going to be one particular point where all the lights turn off at the same time.
10:35It's more like a power outage where different grids go off at different times until, like, there's the one last light bulb that'll just go off.
10:45This is because stars come in different sizes.
10:51The way a star dies has everything to do with the amount of mass it's started life with.
10:56It carries that all the way through its lifetime.
10:59The sun is a medium-sized star, living a stable existence for billions of years.
11:07Giant stars are different.
11:10They live fast and die young.
11:12A star like the sun, which is a medium-sized star, it lives about 10 billion years.
11:20The really massive stars, they live maybe 10 million years.
11:25Massive stars can be tens or even hundreds of times more massive than the sun.
11:31When it comes to lifespan, that's a problem.
11:34A massive star has more fuel to burn in a nuclear sense, so you might naively think that it lasts longer, but it's the exact opposite.
11:46Massive stars can only access hydrogen fuel in their core.
11:51The rest is trapped in the outer layers and can't be used as fuel.
11:56If there's hydrogen in the core, you're good.
12:00If there's hydrogen outside of the core, you can't be used.
12:03If it's not in your fuel tank, it's not doing you any good.
12:08Massive stars also have more gravity than smaller stars.
12:12So, they have to burn their hydrogen fuel faster to prevent the star from collapsing.
12:21They burn their candle on both ends.
12:24Because of their incredible mass, their fusion reactions in the core happen at an incredible rate.
12:30Giant stars are kind of fast and furious.
12:33They are bright, they live their life, and they die very quickly.
12:37When a giant star's fuel runs out, the core collapses catastrophically under the overwhelming force of gravity.
12:48And then, boom, supernova.
12:58The death of a giant star triggers one of the biggest bangs in the universe.
13:03The blast would instantly vaporize nearby planets.
13:15But, these star deaths are also critical for life.
13:20When massive stars die, they release heavy elements they've been making through the course of their lives.
13:26And sometimes they even make new ones.
13:28And it's these heavier elements that are essential for life.
13:33We owe our existence to stars that formed billions of years ago.
13:42In May of 2018, we spotted evidence of ancient stars creating the stuff of life.
13:49We picked up an infrared light signal from a distant galaxy named MACS 1149-JD1.
14:00The signal was ionized oxygen.
14:06It's been traveling for 13.3 billion years.
14:10So the oxygen formed when the universe was very young.
14:14Just 500 million years after the Big Bang.
14:20This oxygen formed in the hearts of massive stars.
14:25The presence of oxygen tells us that there needed to be massive stars in the early universe.
14:31In order to synthesize hydrogen and helium into heavier elements like oxygen.
14:36And then explode to eject that oxygen back into the interstellar and intergalactic medium.
14:45Extreme pressure in the cores of the stars produces oxygen.
14:49Supernova blasts spread these elements across the universe, helping to create new generations of stars.
15:04And, most importantly, us.
15:07If there is one single fact that you should care about in all of science, and this is my favorite fact,
15:15is that you and I are a consequence of star death.
15:22Before you can have life, you need to have the kind of elements out of which life forms.
15:27You need carbon.
15:28You need nitrogen.
15:29You need oxygen.
15:30You need the elements that are the backbone to the biology that makes us possible.
15:35Where did those elements come from?
15:38Well, they came from stars.
15:39They came from stars that formed in the early universe before even the sun existed.
15:44The huge size of massive stars quickly signs their death warrants.
15:50Their explosive ends help create new stars.
15:53And even life.
15:56The fact that you exist at all is because of stars.
16:00But, probing galaxies across the universe, we've discovered something else.
16:08The star apocalypse isn't just killing stars.
16:12It's stopping them from ever being born.
16:16Star formation is dying, and in fact it's dying rather quickly.
16:20The universe right before our eyes is becoming a darker place.
16:23It's running out of fuel, and eventually no more stars will be made at all.
16:29Life on Earth follows a series of regular patterns.
16:54Day after day, the sun rises and sets.
17:03And stars light up the darkness of the night sky.
17:07The reason I got into astronomy to begin with was because I grew up in a rural part of the country,
17:12and the sky was beautiful and dark.
17:14You go outside at night, and you look up, and you can see thousands of stars.
17:18But it won't be that way forever.
17:202016, a network of telescopes across the world measured the energy output of over 200,000 galaxies.
17:34They discovered that in the past 2 billion years, the universe has lost half its brightness.
17:42The night sky is getting darker as stars flicker out of existence.
17:47About 10 billion years ago, the universe kind of hit its peak, and lots of stars were shining.
17:56It was an incredibly bright place.
17:58But in the last couple billion years, it's really, overall, become a less bright place.
18:04The darkening universe isn't just a sign that stars are dying.
18:08It seems there's a problem with star birth, as well.
18:15When we look into the universe's past, what we find is that long ago, stars were forming at a much higher rate.
18:22Right now, what we see is that really, stars are dying off faster than they're being born.
18:26A Milky Way-type galaxy today produces about 7 stars per year.
18:33However, 11 billion years ago, a galaxy like our own would have produced 10 times more stars.
18:38In the early universe, old stars died, and new ones formed in their place from the material left over.
18:48It was the cycle that kept the cosmos bright.
18:52Not anymore.
18:53It kind of sucks for us.
18:57We like a bright universe.
18:59We like all this energy and life that's vibrating through the universe.
19:03But that's just not always going to be the case.
19:07The universe is already winding down.
19:12One of the biggest mysteries in galaxy evolution is figuring out how galaxies stop forming their stars.
19:18We really don't know the answer yet, and it's really important for us to figure out why.
19:24Because, in the end, stars really equal life.
19:30To find out what is shutting off the stars, we study galaxy clusters.
19:39These giant regions of space contain hundreds of galaxies bound together by gravity.
19:45Slowly, the clusters pull new galaxies into them, causing something strange to happen.
19:55What we see happening when a galaxy falls into a cluster is that its star formation is quenched.
20:01It's shut off.
20:03The cause of this quenching effect has baffled scientists for decades.
20:08Then, in October of 2018, an international team of astronomers investigated this long-standing mystery.
20:20They tracked variations in quenching across 14 galaxy clusters and found a possible explanation.
20:28The ability a galaxy has to make new stars is related to the larger environment it finds itself in.
20:35In clusters of galaxies, where many galaxies are orbiting around each other,
20:40we see interactions that strip gas and dust away from galaxies.
20:44The stuff that makes up stars literally just thrown off into space.
20:48Stars form from dense parcels of cold gas, something galaxies are filled with.
20:58But, when a galaxy is dragged into a cluster, everything changes.
21:03Clusters of galaxies contain a lot of hot gas,
21:07whereas you need cold gas inside of a galaxy in order to form stars.
21:10And when a galaxy is moving through this hot gas,
21:14then the cold gas inside is stripped away.
21:18If this new study is right,
21:21and galaxy clusters are stripping away star-forming gas,
21:25new starlight will become rare.
21:29Looking over the history of the universe,
21:32and how much gas was out there and how much is still left,
21:35I think it's fair to say that most of the stars that will ever be made
21:39already have been made.
21:41They've already been born.
21:44Thanks to the shortage of star-forming gas,
21:47stars won't just be dying in the universe.
21:51They'll go extinct.
21:53And the first to go will be the largest.
21:57As the universe runs out of gas,
21:59and fewer of these stars are being made,
22:01eventually, sometime in the future,
22:03all the high mass and even medium mass stars like the sun,
22:06they'll be gone.
22:08What does that mean for life?
22:09Some of the brightest stars will disappear forever,
22:17begging the question,
22:19can life survive the monsters the dead stars leave behind?
22:24The long-term fate of the universe is not a pretty sight.
22:30Some very interesting creatures can start to appear.
22:33In the star apocalypse,
22:52the first stars to fade away will be the brightest.
22:55The giant stars followed by the mid-sized suns.
23:02The universe will become unrecognizable.
23:07The far future will be a very dim universe,
23:10especially for creatures like us.
23:11If there's no more gas,
23:14no more new stars,
23:15it gets dark.
23:17Scared of the dark?
23:19You will be.
23:21Because a hundred billion years from now,
23:24in the shadows of this new universe,
23:27monsters will come out to play.
23:30Now we find ourselves in the era of stars and starlight.
23:34What comes after you could think of as the era
23:36of the dead corpses of old stars?
23:38We already see the corpses of dead stars
23:43scattered throughout the cosmos.
23:46Black holes,
23:49pulsars,
23:50white dwarves.
23:52What happens when more stars die out
23:55and the dead take over?
23:58Can life survive?
24:00It's actually possible that life in the universe will survive.
24:03But we're going to have to get more creative.
24:05January, 2019.
24:10The Gaia satellite studied 15,000 white dwarves
24:14within 300 light years of Earth.
24:18These are the corpses of sunlight stars.
24:22White dwarves are the remnants,
24:24the cores of stars like the sun after they die.
24:27There's no more fusion going on inside of a white dwarf,
24:30so it's just kind of sitting there cooling off.
24:32But it turns out there's a slight reprieve.
24:37The white dwarf corpses usually cool off and dim
24:41over tens of billions of years.
24:44Gaia's data showed something different,
24:48something we've never seen before.
24:51Some of the older dead stars aren't dimming at all.
24:54We used to think that white dwarves could really only dim over time.
25:00After all, there's no source of fusion,
25:02no source of energy in their interiors.
25:04But new studies with the Gaia satellite
25:07have shown that there must be some other energy source
25:10keeping those older white dwarves shining bright.
25:13Something is giving these white dwarf corpses a spark,
25:20bringing them back from the dead as zombies.
25:24The leading contender is that the insides of white dwarves
25:28actually crystallize.
25:30Up to six billion years after dying,
25:35the hot carbon and oxygen matter inside the white dwarf
25:39cools and crystallizes, becoming solid,
25:43giving the dead star a lifeline.
25:46This actually releases energy.
25:49As the star cools,
25:51it winds up releasing a little bit more energy than otherwise would.
25:54This unusual heat source
25:56could warm up a nearby frozen planet,
26:00giving life a second chance.
26:03There will be some extra energy available from these objects.
26:07So this is the time that we have to cuddle up close to the zombies.
26:12Crystallization can rejuvenate old white dwarves.
26:17And the process could even provide
26:19a spectacular setting for an orbiting planet.
26:22We have a special name
26:25for cooled down crystallized carbon and oxygen.
26:28We call them diamonds.
26:30The long-term fate of our universe
26:32will be sprinkled with all these glittering diamonds.
26:37A zombie that comes to life
26:39and shines like a diamond
26:41might be pretty to look at,
26:43but it's still no guarantee
26:44that life could survive here.
26:47You can kind of think of these white dwarves
26:52as maybe making a little more energy for the universe,
26:55but even that's going to eventually run out.
26:58The whole thing becomes a gigantic crystal.
27:01And again,
27:02it's just going to start cooling and fading away.
27:04The zombie fizzles out into a dark cinder,
27:09giving off almost no light at all.
27:13But there's another monster lurking in the cosmos.
27:16When a star that's much more massive than the sun dies,
27:23it explodes violently.
27:25And during that explosion,
27:27the core collapses
27:28and becomes an incredibly dense small object,
27:31one of the most wonderful real monsters in the universe.
27:35This is a pulsar.
27:39PSR B0329 plus 54.
27:443,000 light years away from us.
27:47The pulsar has the mass of the sun,
27:50but it's just 12 miles across.
27:53Its rapid spin generates beams of radiation from its poles,
27:58bringing the zombie to life.
28:00Now, we've discovered an alien world
28:04orbiting this zombie star.
28:08In 2017, a new planet was discovered around a pulsar.
28:13They're about twice the mass of the Earth,
28:16and that's really incredible.
28:18The pulsar planet sounds intriguing,
28:21but the prospects for life aren't good.
28:25Orbiting a pulsar would be a brutal environment for life.
28:30It's highly unlikely that there's life
28:32because the radiation from the system
28:34would be overwhelming
28:35and likely blow away the atmosphere.
28:40As for sustaining life in the universe,
28:43none of these options is what you'd call a safe bet.
28:49These are momentary reprieves from the inevitable.
28:53No matter what you do,
28:54eventually you're going to run out of these gimmies.
28:57You're going to run out of the get-out-of-jail-free cards.
29:00Inevitably, everything is going to cool and fade away.
29:07This might be game over for stars,
29:09and even for life.
29:12But there is still a glimmer of hope
29:15hidden in the cosmos.
29:18A star that isn't dying.
29:20It appears blessed with eternal life,
29:24and its color is red.
29:27Red dwarfs.
29:28We are literally surrounded by them,
29:31but they are largely invisible to us.
29:33Illuminating every corner of our night sky
29:49is the light of stars.
29:53But what we see with the naked eye
29:56doesn't tell the whole story.
29:58The stars that you're seeing
30:01are mainly stars like the sun
30:03or even more massive
30:04and even hotter than the sun.
30:06They're bright.
30:06You can see them from a distance.
30:08But amazingly,
30:09the most common form of star,
30:11by far,
30:13are the red dwarf stars.
30:14They're up there right now in the sky,
30:16but they're just too small
30:17and too faint to see.
30:20Red dwarfs are up to 10 times smaller than the sun,
30:23and they burn less brightly.
30:26Right now,
30:27hidden in the night sky,
30:29over three quarters of the stars in our galaxy
30:31are red dwarfs.
30:35And while the larger stars are dying out,
30:38we've never seen a red dwarf die,
30:41making them the best bet for life to survive
30:44the star apocalypse.
30:46When the most massive stars
30:49eventually go out
30:51and are not replaced,
30:53what will be left
30:54are much, much dimmer stars
30:56like red dwarf stars.
30:58We've seen star death across the universe.
31:02So why not red dwarfs?
31:04Turns out,
31:06their size gives them a crucial advantage
31:08over larger stars.
31:10The more massive a star is,
31:12the hotter it burns.
31:13A red dwarf star burns at a lower temperature,
31:15so it doesn't burn through its fuel
31:17quite as quickly as a mid-mass star does.
31:20These are like the economy cars of the universe.
31:23They're just sipping on their nuclear fuel,
31:25and they can coast along.
31:28Not only that,
31:30despite being smaller,
31:31they have access to more fuel.
31:35Our mid-sized sun is split into three layers.
31:39A core,
31:40a radiation zone,
31:41and a convective layer.
31:43The radiation zone prevents hydrogen in the top layer
31:47from ever becoming available for the core to burn.
31:50So,
31:51the sun can only access about 10% of its total hydrogen fuel.
31:57Once the hydrogen in our sun's core runs out,
32:02its days are numbered.
32:04In some ways,
32:05these mid-sized stars end up starving themselves.
32:08The smaller red dwarfs are different.
32:12They can access all the hydrogen they want.
32:14In low-mass stars,
32:17outside of the core,
32:18this outer layer is fully convective.
32:21What that means is,
32:23stuff near the core rises to the surface,
32:25and then drops back down all the way to the core.
32:28And that means,
32:29if you have hydrogen somewhere outside of the core,
32:32eventually,
32:32it's going to make its way down there,
32:34and it can be used for fuel.
32:36The red dwarf has access to everything
32:38at the all-you-can-eat buffet.
32:39It can grab stuff from the distant regions
32:42at the surface of the star,
32:43and bring it all the way down the gullet
32:46to the heart of the star.
32:49This all-you-can-eat hydrogen buffet
32:51extends the lifespan of red dwarfs
32:54to incredible lengths.
32:56The universe is over 13 billion years old,
33:00but any red dwarf that age is a toddler.
33:05A red dwarf,
33:06even if it was born at the very beginning of the universe
33:09when red dwarfs could first form,
33:11even today,
33:12it's just a tiny fraction of its lifespan.
33:15They can last for trillions of years,
33:17thousands of times the current age of the universe.
33:2113 billion years old,
33:22that seems like a long time,
33:24but a small red dwarf,
33:26it's barely out of diapers.
33:30Red dwarf stars will not die out
33:33for 10 trillion years or more.
33:36And we're discovering
33:38they have another trump card
33:40that's good news for life.
33:46February 2017,
33:49NASA announced the discovery
33:50of a system in the Aquarius constellation
33:53called TRAPPIST-1,
33:54where seven Earth-sized planets orbit a red dwarf star.
34:01It turns out that red dwarfs, apparently,
34:05are really good at making planets,
34:07including planets that are roughly the size of the Earth.
34:11That's really cool,
34:13because these stars last a long time.
34:16If they have planets orbiting them with life,
34:18they could outlast our solar system
34:20by trillions of years.
34:24Sounds promising,
34:25but red dwarfs have an ugly side.
34:30In October 2018,
34:33astronomers turned the Hubble Space Telescope
34:35to a series of young red dwarf stars
34:38in the Tucana Horologium Association.
34:41They witnessed these infants
34:44throwing daily stellar tantrums.
34:48Even though they're the smallest stars,
34:50they actually have some of the strongest flares
34:52and storms on them.
34:54Red dwarfs can emit flares
34:5610,000 times more powerful than the sun.
35:00These flares would cook any nearby planets.
35:04When a red dwarf star forms,
35:07they're rotating very rapidly,
35:09and this creates a lot of magnetic activity,
35:11which creates flares and mass ejections.
35:15For life to exist,
35:17it would have to wait
35:18for infant red dwarfs to grow up.
35:22As a red dwarf gets older,
35:25there's drag between the magnetic fields in space
35:28as it rotates,
35:29and that has the effect of slowing down
35:31its rate of rotation,
35:32and so this means the activity settles down.
35:34So maybe later in the life of a red dwarf star,
35:38they can support planets with life.
35:43Red dwarf stars will dominate the future universe
35:47and may give life a chance to survive.
35:51These small red stars are extremely long-lived,
35:55but no star is immortal.
35:58Even though they're really going through
36:00their nuclear fuel very slowly,
36:03there's just not enough fuel to last forever.
36:07These little stars will die out eventually.
36:11Unlike their larger, stellar siblings,
36:14they'll go quietly.
36:16But actually just gets hotter,
36:18and the color of a star depends on its temperature.
36:21So as the red dwarf gets hotter,
36:23it turns bluer.
36:24So sometime in the very distant future,
36:27some of these red dwarfs
36:28are actually going to become blue dwarfs.
36:31The universe isn't old enough
36:33for blue dwarfs to exist yet.
36:36But trillions of years from now,
36:38a dim blue glow
36:40will complete the star apocalypse.
36:42There will be a last star,
36:47one last red dwarf,
36:49maybe now turning blue as it warms up.
36:52But it too will eventually cool off,
36:55fade away.
36:56And there will be no more stars in the universe.
36:59It is inevitable.
37:03In this dark, starless universe,
37:05prospects for life seem impossible.
37:09But will something else
37:11take the place of stars?
37:14As we get to the end of the universe,
37:16things get really cold,
37:18but they also get really weird.
37:19Trillions of years from now,
37:37the star apocalypse
37:39will leave the universe
37:40empty and dark.
37:43A never-ending night.
37:46The universe at this time
37:48is nothing like the universe of today.
37:50There's no light
37:51and it's really cold
37:53and very lonely.
37:56When all of the stars die
37:58and the light goes away,
37:59anything that relies on the heat
38:01and the processes from these stars
38:03will start to die.
38:06Once all the lights go out,
38:08the only things that will remain
38:10will be the leftovers.
38:12With stars as we know them long gone,
38:15could something else spark into existence?
38:18In this cosmic wasteland?
38:20You'd think that's it,
38:22no more star formation.
38:23But the universe still has
38:25a few tricks up its sleeve.
38:27Over the history of the universe,
38:29generations of stars have lived and died.
38:33They released heavy metal elements
38:34into the universe,
38:36building materials
38:37for a new kind of star.
38:39And stars born from these new materials
38:42can do things
38:43their ancestors could not.
38:46As you enrich the universe,
38:49as more and more metals
38:51get produced over time,
38:52you can lower the temperature
38:55needed for fusion reactions
38:58in a star.
38:59With lower temperatures
39:01needed for fusion,
39:02stars have become
39:04smaller and smaller.
39:06Currently, the smallest possible star
39:09is a little under 10%
39:10the sun's mass,
39:11but eventually it may be possible
39:13to form stars
39:14that have around 4%
39:15the sun's mass.
39:18Hundreds of trillions
39:19of years in the future,
39:21a new star
39:22may dominate
39:23the universe.
39:25Built from scraps
39:26left over
39:27from generations
39:28of dead stars.
39:31A star so small
39:32that it burns
39:33cold
39:34instead of hot.
39:35One of the weirdest
39:38types of stars
39:39that scientists hypothesize
39:40might exist
39:41in the far future
39:42is the frozen star.
39:46You can start
39:46forming stars
39:47that are very,
39:48very small
39:49and very cold,
39:51where nuclear fusion
39:53is happening
39:54in the core,
39:55but the surfaces
39:56are cold.
39:57These small,
40:02cold objects
40:03will be thousands
40:03of times dimmer
40:05than the faintest star
40:06we see today.
40:08So cold,
40:10the temperatures
40:11on the surface
40:12could reach
40:12just 32 degrees Fahrenheit,
40:15and ice clouds
40:16may form
40:17in the star's atmosphere.
40:20They are so much
40:21cooler than stars now,
40:23they could actually
40:24have ice,
40:25water ice,
40:27on their surface,
40:28even though
40:28they are technically
40:30stars.
40:31It's literal
40:33water ice
40:34covering the surface
40:35of a star.
40:36The same ice
40:37that you can use
40:38for ice skating
40:39or ice racing
40:40or curling,
40:42you could do
40:42all of this
40:43on the surface
40:44of a star
40:45in the far future.
40:47It's hard to predict
40:49if life could arise
40:50on planets
40:51orbiting
40:51frozen stars.
40:55We won't know,
40:57until one appears.
40:59And that won't be
41:01for a very
41:02long time.
41:05The universe
41:06is far too young
41:07for even the first
41:08one of these things
41:09to even be a glimmer
41:10of an idea.
41:11So if you want to wait,
41:13you know,
41:13a quadrillion years,
41:14eh, we can find out.
41:16Stars
41:17helped create us,
41:19building and spreading
41:20the ingredients
41:21for life to develop.
41:22But the coming star
41:24apocalypse
41:25may mean
41:26the end of life.
41:27Just
41:28not for a while.
41:31Small red stars
41:33will continue
41:34to illuminate
41:35the darkness.
41:36Safe havens
41:37for life to survive
41:38and even flourish.
41:41As for us
41:42on Earth,
41:43we should be
41:43most thankful
41:44for one star.
41:46because
41:47without it,
41:48we simply
41:49wouldn't exist.
41:51I really want you
41:51to never experience
41:53a sunny day again
41:53and not think about this.
41:55The sun someday
41:56will burn out
41:57and so will
41:58all of the other stars.
42:00We are in this
42:01wonderful era
42:02of light
42:03and warmth
42:03coming out of the sky
42:04and everything
42:06is going to go dark.
42:07Absolutely everything,
42:09everywhere in the universe.
42:11So for the time being,
42:13you know,
42:13enjoy the light.
42:14Step outside,
42:15enjoy the sun
42:16and think about
42:17how lucky we are
42:18to live in this time.
42:19the sun
42:47in the universe.