How the Universe Works

Imagine a universe with no stars...

a dark, endless night.

This is not some Sci-Fi nightmare.

This is our future.

There will definitely be a point in the future when, you look up,

you will no longer be able to see stars.

Things really will get darker and darker,

until there will be almost no memory of light left.

For billions of years, stars brought life to the universe.

The fact that you exist at all is because of stars.

Now, they're dying out in a star apocalypse.

The effect could be tremendous.

It can permeate throughout the universe.

What's causing the die-off,

and what happens to life when the lights go out?

Eventually, the whole entire universe

starts to get a little bit weird.

captions paid for by discovery communications

for over 4.5 billion years,

the sun has bathed our home planet with light.

Its bright, stable glow helps life flourish,

but hidden in the night sky,

other planetary systems haven't been so lucky.

Hanging right above your head every night,

we see up there these dead corpses of stars.

400 light-years from earth lies a system called SDSSJ1228.

A disk of debris orbits

the faintly glowing leftovers of a dead star.

J1228 is a dead star.

It is a core of a star that had aged,

blown off its outer layers, revealed the core...

which is about the size of the earth,

but has about half the mass of the star in it.

And we call these "white dwarfs."

May, 2018.

Astronomers investigated J1228

using the world's largest optical telescope...

the Gran Telescopio Canarias.

They discovered what appears to be a ball of iron

orbiting the white dwarf.

The lump of metal, less than 400 miles across,

could be the exposed core of a destroyed planet.

It's a clue to this system's past.

It's always a little poignant

when you see evidence of a planet around a dead star.

You know, you think back of when that star was shining,

and could there have been life in that solar system?

The J1228 system is a cosmic graveyard.

It might look different than our solar system,

but this is our future.

This discovery of a dead planet orbiting a dead star

is like looking into a crystal ball.

And is it the future of our own solar system?

Yep.

For a glimpse into your future, you know,

all you need to do is look up.

Just like J1228, our sun will die,

killing off earth in the process.

This terrifying fate will play out across the galaxy

in a star apocalypse.

Our sun is a fairly common type of star in the milky way,

and so, other stars in the milky way

will undergo the same sort of fate as the sun.

They will end up as white dwarfs.

And so, any other planets out there orbiting sun-like stars

will undergo a similar fate.

Once the stars like our sun have died out,

what's gonna happen?

Could life still survive around white dwarfs?

To understand the fate of sun-like stars,

we have to look inside them.

Buried within are clues to how they live, and why they die.

The core, the very center, that's where the action is.

That's where the star is fusing light elements

into heavier elements.

And that works like a hydrogen bomb.

It's the same thing.

If you compress hydrogen enough, it gets very hot,

and the pressure gets very high,

and if fuses into helium, and generates energy... heat.

And that's what's happening in the core of every star.

Because of their enormous mass,

stars have huge amounts of gravity.

This gravity pushes inwards, trying to collapse the star,

but fusion energy from the core stops that from happening.

It's really this sort of very balanced dance

between gravity pushing in, fusion energy pushing out.

You can think of a star as losing energy,

continuously, to the outside world/

and gravity is saying, "yes, I'm gonna take over."

But, no, the nuclear reactions inside a star

replenish the energy that's lost,

and keep the star hot and pressurized inside,

so that the pressure-gravity balance can be maintained.

This balance keeps sun-like stars alive

for up to 10 billion years,

until the star's gas tank runs dry.

It's gonna run out of fuel.

And when that happens, it's going to die.

But what is that gonna look like?

How is this gonna happen?

One hundred million years ago,

things in the J1228 system started to get ugly.

First, the star grew large... really large.

Once the center starts fusing heavier elements,

the outside will swell

into what will eventually be a red giant star.

J1228 transformed into a red giant.

Its outer layers blew off,

extending out over 40 million miles.

When stars like our sun die, it's not a quiet affair.

It's very violent, and ugly, and messy.

They turn into red giants,

and they turn themselves inside out,

and vomit all over the solar system.

When J1228 swelled into a red giant,

nearby planets were stuck in a kill zone.

The dying star engulfed them, or fried them

with temperatures of over 1,200 degrees Fahrenheit.

Atmospheres disappeared.

Oceans boiled away,

but one planet survived J1228's death throes.

Here's a case where a planet survived, in some sense,

the death of its own star, and it's still hanging around,

still hanging on, hoping for something new.

The red giant's expanding outer layers

separated from the star's core.

With no active fusion, the core collapsed into a white dwarf.

The white dwarf's dense gravity

then went to work on the one surviving planet.

The planet that might've been orbiting the normal star

can gradually spiral in toward the white dwarf,

and then, eventually, the gravity of the white dwarf pulls

on the near side of the planet more than on the far side,

and that tears it apart.

What we're seeing here is a dead star

dining on its own solar system.

That's what is in the future for the sun.

J1228 feasted on the remains of its rocky worlds,

leaving behind a disk of debris and the planetary core.

It's a glimpse of earth's future.

What happened here around this white dwarf

is gonna happen to earth.

It's gonna be stripped of its atmosphere,

its crust, and its mantle,

and the only thing that will remain will be the core.

Fried and ripped apart by a dying star...

not a good way to go.

Fortunately, for life on earth,

our own sun isn't dying just yet.

The sun is middle-aged.

It's 4.5 billion years old,

and it's going to go on for another 5 or 6 billion years.

We've got a little bit of time

before our sun pukes all over the solar system.

Our home planet may be safe for now,

but systems like J1228 show us

that sun-like stars are destined to die,

killing off any life orbiting them.

But sun-like stars aren't the only stars

dying across the cosmos.

There are others out there, and they're all doomed.

There's a wonderful rainbow of stars

out there, of all different shapes,

all different sizes, and all different colors.

We're talking down to, you know,

fractions of the mass of the sun,

up to hundreds of times the mass of the sun.

When it comes to the star apocalypse, size matters.

The bigger and brighter the star, the faster it dies.

Our universe is a vast expanse of death and destruction.

All of the stars are destined to die, but not all at once.

There's not going to be one particular point

where all the lights turn off at the same time.

It'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.

This is because stars come in different sizes.

The way a star dies has everything to do with

the amount of mass it started life with.

It carries that all the way through its lifetime.

The sun is a medium-sized star

living a stable existence for billions of years.

Giant stars are different.

They live fast, and die young.

A star like the sun, which is a medium-sized star,

it lives about 10 billion years.

The really massive stars,

they live maybe 10 million years.

Massive stars can be tens or even hundreds of times

more massive than the sun.

When it comes to life span, that's a problem.

A 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.

Massive stars can only access hydrogen fuel in their core.

The rest is trapped in the outer layers,

and can't be used as fuel.

If there's hydrogen in the core, you're good.

If there's hydrogen outside of the core, it can't be used.