How the Universe Works

The universe is home to real monsters.

We can't see them, but we know they're out there.

You really can't get anything bigger or stronger or scarier

than a black hole.

Black holes consume planets and stars...

anything that gets too close.

Black holes give physicists no end of headaches,

'cause they break all the rules.

But they rule the universe.

They are center-stage.

We now know they dominate

the evolution of the universe itself.

Black holes are the most mysterious objects

in our universe.

Their gravity is absolute.

Nothing can escape.

They can suck in whole galaxies.

Black holes used to be science fiction.

Now we know they're real.

When I was a PhD student,

people used to giggle when you'd hear about black holes.

They're like unicorns, mythical creatures.

We called this the "giggle factor."

People would say, "Beam me up, Scotty."

Well, no one is laughing anymore.

So, they're not science fiction.

Even though we've never landed in one,

we have enough evidence to know that they're really out there.

This image might not look like much to you and me,

but to a scientist, it's proof that black holes exist.

It's an actual movie of a black hole devouring a star

in the constellation of Aquila.

Black holes are messy eaters.

The red spots you see are gas

that's being spit out of the hole, into space.

Eventually, over the next million years,

this star will be eaten alive and disappear.

A black hole is pretty much the end point of everything.

It's the end point of a star. It's the end point of matter.

It's the end point of energy. It's the end point of gravity.

I mean, that's really it. That's the top of the scale.

Although they have the power to destroy

like nothing else in the universe,

black holes also help build galaxies...

a vital part of the great cosmic machine.

Some astronomers think

they could even be gateways to parallel universes.

We are now entering the golden age of research

in black-hole physics.

They could be the key

to understanding the birth of the universe,

its formation, and then its death.

Black holes really represent,

in one sense, the frontier of modern astronomy.

And they're changing our ideas about how galaxies form

and, indeed, how the universe works.

Their power comes

from one of the primary forces in nature... gravity.

I teach astronomy.

And we teach our students

that the fundamental principle of gravity is, "gravity sucks."

Gravity keeps our feet on the ground

and our planet orbiting around the Sun.

But in a black hole, the force of gravity is off the charts...

so strong, it sucks in anything nearby.

It can even bend the light from distant stars.

And if that light gets too close,

the black hole swallows it.

Think of it like this.

Imagine a black hole as a waterfall.

Gravity is the river flowing toward the falls,

and a beam of light... the kayak.

Upriver from the waterfall, the current is weak.

The kayaker can paddle against it and get away.

But closer to the waterfall, the current is stronger,

and the kayaker struggles to escape.

The edge of the waterfall is like the edge of a black hole.

No matter how strong the kayaker is, he's going down.

It's the same in space.

The way black holes are really devastating

is because when you get close to them,

the gravity gets super-strong.

So strong that they eat light.

That's why black holes are black.

A black hole is like a roach motel.

Everything checks in. Nothing checks out.

Anything that gets too close is doomed...

planets, stars, even whole solar systems.

And don't think this is some faraway phenomenon.

Black holes are on the loose

right here in our own cosmic neighborhood.

We now know there are wandering nomads

throughout the Milky Way galaxy...

vagabonds throughout the galaxy,

where black holes can come up right behind you

and perhaps gobble you up, and they won't even burp.

If one ever comes close, watch out.

If a black hole found its way into our solar system,

it would rip us apart.

Any kind of black hole

that could pass through the solar system

would be pulling on all the planets

harder than the Sun does.

And so it's just gonna totally disrupt

the gravitational balance of the solar system.

The black hole would literally tear planets from their orbits

and smash them into each other.

It's just an epic disaster. It's a bull in a china shop.

If it got close enough to, say, Jupiter,

it could actually pull the moons of Jupiter

away from the planet itself.

It would just be flinging planets left and right

everywhere as it whipped through the solar system,

leaving disaster in its wake.

If a black hole approached Earth,

all that gravity would rip asteroids from their orbits

and hurl them toward our planet.

The Earth's surface would become an inferno.

It would be the beginning of the end.

First, it would swallow up the atmosphere,

then the planet itself.

Destroying an entire solar system

is nothing to a black hole.

But it's more than just a big, empty, sucking piece of space.

It's incredibly heavy.

To get an idea just how heavy and dense a black hole is,

imagine the Earth.

Now start to crush it...

...and keep crushing until it's packed so tight

even the atoms themselves collapse.

When the Earth crushes down to just 2 inches across,

that's the density of a black hole.

It would be the size of a golf ball,

yet weigh the same as the Earth, with the same amount of gravity.

What can make something that small,

that dense, and that powerful?

We don't have external forces, large pistons in the universe,

to create black holes.

So the only way the real black holes of the universe form

is if gravity can do the job itself.

There is only one place in the universe

that generates that much gravity.

And it's inside the largest stars.

When massive stars 10 times heavier than our sun die,

gravity crushes them,

creating a huge explosion, a supernova.

But some stars are even bigger than that.

These supermassive stars weigh 100 times more than our sun

and have 100 times more gravity.

When one of these stars dies,

it sets off the biggest explosion in the universe...

A hypernova.

This is the birth of a black hole.

Our universe is full of stars.

At the end of their lives, some die quietly.

Others go out in spectacular explosions.

And some give birth to black holes.

If you have a star,

a supermassive star that's 100 times the mass of the Sun,

at the end of its life, the core runs out of fuel.

There's nothing left to hold it up,

and the core collapses down into a black hole.

When that happens, the enormous gravity

generated at the heart of supermassive stars runs wild.

This is the dying star V.Y. Canis Majoris.

It's more than a billion kilometers across.

Like all stars, it's a giant nuclear-fusion reactor,

pumping energy outward.

At the same time, the star's extreme gravity crushes inward.

For a few million years,

fusion and gravity are locked in standoff.

But when the star runs out of fuel,

fusion stops and the stalemate ends.

Gravity wins.

In a millisecond,

the core shrinks to a fraction of its original size

and a baby black hole is born.

Immediately,

it starts to cannibalize what's left of the star.

As matter swirls into the black hole, it gets incredibly hot.

And there are magnetic forces and frictional forces,

and it's just a witch's brew, a nightmare,

what's going on right above the surface of the black hole.

The new black hole in the middle

keeps feeding on the body of the star around it.

It eats the gas so fast, it chokes and coughs,

blasting out huge beams of energy.

They basically eat their way out from the star.

This happens in milliseconds.

It happens before the rest of the star even knows

the core is gone.

And so basically, the star is dead before it hits the ground.

Finally, the star explodes.

In one second, it blasts out 100 times more energy

than our sun will produce over its entire life.

What's left is a new black hole and two jets of energy

hurtling through the universe at the speed of light.

These jets are called "gamma-ray bursts."

They're incredibly energetic events.

In terms of raw energy and power,