All language subtitles for How the Universe Works s01e02 Black Holes.eng

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 miles 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,

gamma ray bursts are second
only to the Big Bang itself.

Most of them last
only a few seconds.

And they fry
anything in their way.

They're so intense that
if there was a gamma-ray burster

in the region of our galaxy
near our solar system,

it could literally vaporize
the entire planet.

Fortunately, most gamma-ray
bursts occur outside our galaxy.

But they tell us
something important

about black holes
and how our universe works.

What we were seeing every time
a gamma-ray burst went off

was basically
the birth cry of a black hole.

By counting gamma-ray
bursts, astronomers can figure out

how many black holes
are being created.

In 2004, NASA launched
the Swift probe

to scan the universe
for gamma-ray bursts.

Five...

four...

three...

two...

one...
We have ignition.

And we have lift-off
of NASA's Swift spacecraft,

on a mission to study
and understand gamma-ray bursts

throughout the universe.

This is the most
powerful gamma-ray burst

Swift has detected so far.

The flash of light announces
the birth of a new black hole

on the other side
of the universe.

Swift can only look at
a fraction of what's out there.

Still, it detects at least
one gamma-ray burst every day.

That discovery rocked astronomy
to its foundations.

We once thought
that black holes, like unicorns,

could never be found.

We now believe that there are
perhaps billions of black holes

in the night sky.

When we look around our galaxy
and other galaxies,

it's clear that the universe
is full of powerful black holes.

Finding black holes
is one thing.

Figuring out how they work...

that's a whole different
ball game.

The only way to find out
is to visit one.

You'd have to take a spacecraft
across the vastness of space

just to get close to it.

Then you'd have to go
inside the black hole.

There, you'd find a place

where reality breaks down
and time stands still.

There are billions
of black holes in the universe.

We can detect them
with telescopes and satellites.

But we don't actually know
what they're like up-close.

It's a long way off,

but scientists
are already speculating

about a mission
to a black hole...

A one-way trip to the most
dangerous place in the universe.

Originally,

physicists were horrified
at the idea of black holes.

They wanted to banish them,

because the laws of physics,
as we know them,

seem to break down
at the instant of a black hole.

Time stops.

Gravity becomes infinite.

This is a nightmare.

Obviously, we can't send
humans anywhere near a black hole.

But a robot?
Well, sure.

A robotic probe
could transmit data back

just before
it goes over the edge.

That edge of a black hole
is called the "event horizon."

It's the edge
of time and space...

at least,
in the universe we know.

We call the event horizon
"event horizon"

quite simply because

it separates space
into two regions.

It's not a physical surface.

You might not even notice it
if you were falling through it,

but ultimately, once you're
inside of it, you're doomed.

As you approach
the event horizon,

gravity gets stronger

and very strange things
start to happen.

As you fall
into a black hole feet-first,

your feet are closer
to the black hole.

And so the gravity they feel
is stronger.

Your head is not quite as close,

and so the gravity it feels
is less.

And basically, what happens is,
you get stretched out.

Your feet are being pulled
much harder than your head,

and you're like a piece of taffy

being pulled
between two strong people.

As you get thinner
and thinner and thinner,

as you get closer
and closer and closer,

you're undergoing a process
we call "spaghettification"

because you're basically turned
into a long, thin tube of pasta.

Gravity would stretch
our robotic probe to the limit,

then rip it apart.

But imagine
if the probe was strong enough

to survive and keep going.

As it gets close to the event
horizon, everything goes crazy.

Gravity is so extreme,
it stops time.

We think of time
as being endless.

However, in a black hole,
in some sense, time stops.

This sounds like it's
nuts, but that's the way it works.

It's in the math.

It's actually woven into the
fabric of the universe itself.

If you were to watch
from a distance,

the robot probe
would seem to slow down

as it gets closer
to the black hole.

Then it would appear to stop
completely.

The whole process
might just take a brief moment.

But from the outside,

you appear to freeze
and fall ever more slowly.

You actually can never observe
an object fall

all the way
through the event horizon.

It literally freezes
at the surface

because its clock
is going infinitely slowly

compared to yours.

In reality,
the probe hasn't stopped at all.

It keeps going
and crosses the event horizon.

If the probe
points its cameras backwards,

towards the entrance
of the black hole,

it will see light
being sucked in.

If it points the camera forward,
at first it sees only black,

but as it moves toward the heart
of the black hole,

it encounters the most bizarre
place in the universe.

The black hole's immense gravity
pulls everything down

to an unimaginably small point
at its center.

Scientists call it
the "singularity."

We really just don't know

what happens
at the center of a black hole.

The densities are so great

that the laws of physics
break down, as we know them.

A singularity is a point
of infinite gravity,

where space and time
become meaningless.

Now, that is ridiculous.

A singularity is basically a
word for saying "I don't know."

It's a word for saying
"I'm clueless."

Even now,

scientists can't really answer
the question,

"What is a black hole?"

It's upsetting, a little bit,

to think that there are objects
out there

that are breaking
the laws of physics.

There must be bigger laws

that are being used
by these black holes,

that are being obeyed
by these black holes,

that we just
don't understand yet.

Okay, so,
the one thing we do understand

is that black holes are born
from dying stars.

And most are small...
around 20 miles across.

But now
scientists have discovered

that some black holes
are much bigger.

They're called
"supermassive black holes."

They're the same size
as our entire solar system.

And one of these monsters lies
at the heart of our own galaxy.

Our solar system lies
in the Milky Way galaxy.

It's made up of billions
of stars, including our sun...

...all revolving
around a mysterious region

right at the center.

Children ask the question...

if the Moon goes
around the Earth,

the Earth goes around the Sun,

then what does the Sun
go around?

It's a good question.

And astronomers ask
the same thing.

Maybe there was something
going on

at the heart of the Milky Way...

perhaps a black hole
at the very center.

But because we can't
actually see a black hole,

the best they could do
was look for telltale signs.

Using infrared telescopes,

they looked
at the middle of the galaxy

and discovered
a densely packed swarm

of millions of stars.

But they couldn't see
what was at the center.

One team has spent 15 years
looking for clues.

High above the clouds
on Mauna Kea, in Hawaii,

the giant Keck telescope
has the power

to see right through
to the center of the Milky Way.

The region
which we have to study

to prove that there's a
black hole is incredibly small.

It is absolutely the case

of looking
for a needle in a haystack,

except we know
exactly where the needle is.

Andrea Ghez
has spent countless nights

scanning
the center of the galaxy

for signs of a black hole.

To be able
to do this experiment,

one has to be able to see

the stars that are very close
to the center of the galaxy

and to position them
incredibly accurately.

And this would be equivalent

to me in Los Angeles
looking at you in New York

and seeing you be able to move
your finger like this.

As the Keck kicks into action,

a laser beam detects tiny
disturbances in the atmosphere

that would distort the image.

Motors then adjust the huge
30-foot mirror to compensate.

The image is clear enough

to track the stars
at the heart of our galaxy.

Ghez has taken thousands of
images over the last 15 years.

And what they reveal is amazing.

The stars
at the center of the galaxy

are moving
at millions of miles an hour.

The center of the galaxy
is a very extreme environment.

The speeds with which stars move

is much higher than
anywhere else in our galaxy.

And that is absolutely
the signpost of the black hole.

They look like tiny planets
racing around an invisible sun.

But they're not planets.
They're stars.

It takes a lot of gravity

to swing huge stars around
in such fast, tight orbits.

There's only one thing in the
universe with that much pull...

a supermassive black hole.

Watching these things
shows the presence

of a 4-million-times-
the-mass-of-our-sun black hole,

located right at the heart
of our galaxy.

It is a huge discovery.

Everything in our galaxy,
including our own solar system,

orbits around
a supermassive black hole.

But the Milky Way
isn't the only galaxy

with a black hole in the middle.

There are
supermassive black holes

at the heart of most galaxies
in the universe.

The Andromeda galaxy
is our closest neighbor.

It circles around
a supermassive black hole

weighing 140 million times
more than our sun.

Other galaxies,
like this one, M87,

have black holes weighing
as much as 20 billion suns.

How do black holes get so big,

and what are they doing
at the center of galaxies?

For answers, we have to go back
nearly 14 billion years

to the beginning
of the universe.

Back then,

the universe was filled with
clouds of gas from the Big Bang.

In some places,

the gas was thick enough
for millions of stars to form.

Most of these new stars
were supermassive.

They burned hot and fast

and then exploded,
creating lots of black holes.

The early universe
was a wild-and-crazy place

where huge regions of mass

were collapsing
catastrophically,

producing black holes.

And, in fact, the early universe
might have been

full of emerging black holes
everywhere.

Gravity pulled
many of them together.

All over the early universe,

they merged, creating
larger and larger black holes.

Over hundreds of millions
of years, each black hole grew,

producing stronger gravity and
pulling in more and more gas.

New stars were born from the
gas, forming primitive galaxies.

But the black hole
kept on sucking in gas,

until it could take no more,

igniting the most powerful
flamethrower in the universe.

A young galaxy
is a vast cluster of stars,

stars that formed
from clouds of gas.

At the center of the new galaxy

is a young, supermassive
black hole feeding on the gas,

getting bigger and bigger.

If you can imagine,

when a galaxy is very young
and still forming,

there's a supermassive
black hole forming at the core,

and the gas
is still falling into it

and still forming the galaxy.

Well,
near that central black hole,

things are getting very hot.

That material is heating up.

Gas is speeding
into the black hole.

But it overloads,

and there is no room
for all that excess hot gas.

It has nowhere to go but out.

It's blasted into space
in huge jets of energy.

Each jet is 20 times wider
than our solar system

and shoots
clear through the galaxy.

The supermassive black hole
has ignited a quasar.

Quasars are literally

the brightest objects
in the universe.

They're so intense, they can
outshine an entire galaxy.

This is a real photograph

of a real quasar
in the galaxy M87,

50 million light-years away.

Quasars blast away
huge quantities of gas

from the surrounding galaxy...

...the equivalent
of 10 Earths every minute.

When you heat up a gas,

it tends to expand
and it blows outward.

And it's sort of like a wind,
but on a huge scale.

And you get a black-hole wind,

gas blowing out
from the black hole.

Black holes suck gas in.
Quasars blow it out.

But eventually there's no gas
left to make stars,

and the galaxy stops growing.

So we think
that the eventual size

that a galaxy can achieve

depends on the black hole
in its center.

The two are tied together.

With no gas left to feed
on, the quasar jets shrink and die.

What's left
is a supermassive black hole

at the center of the galaxy,
with a whole lot of young stars,

just like our Milky Way
back when it was young.

Early on
in the history of the Milky Way,

when it was a young galaxy,
we were probably a quasar.

Probably every big galaxy
was a quasar when it was young.

But right now we're old enough

that the galaxy
has quieted down.

Now astronomers
are looking for quasars,

the secret
to finding more black holes

and figuring out how they work.

The Chandra observatory
is a space telescope

that can detect the powerful
x-rays quasars send out.

It's found thousands.

These remarkable images show

quasars of all shapes and sizes
firing out into space.

Each one is a signpost

for a young galaxy with
a new black hole at its center.

These quasars
will eventually calm down

as their galaxy matures
and takes its final shape.

I guess the universe
is a lot like people...

active when they're young,

a little bit quieter and more
relaxed when they get older.

We now know
that supermassive black holes

and the quasars they create
control galaxies.

Black holes are central
to understanding how galaxies form.

They're a key to understanding
how they evolve with time.

So, in fact,
rather than being obscura,

they're fundamental
to our understanding

of our galaxies
and our universe.

The only way to
find out more about black holes

is to get a good look at one.

And since an up-close visit
is, well, not a good idea,

astronomers are trying to devise
a way to take a picture

of the supermassive black hole
at the heart of our own galaxy.

To get it,

they'll need a telescope
as large as Earth itself.

There's
a supermassive black hole

at the center of the Milky Way.

It's hidden
by a dense cluster of stars

circling
the heart of the galaxy.

But soon,
we hope we'll be able to see it.

Seeing is believing.

It would be spectacular
if we can go right up there,

nose-to-nose
with the event horizon

of the black hole at the center
of the Milky Way galaxy.

And that's the Holy Grail.

A supermassive
black hole lies hidden

at the center of most galaxies.

We only know they're there

because the stars around them
are drawn in

at millions of miles per hour.

But there might still be a way

to take a picture of the
very edge of the black hole...

the event horizon.

Shep Doeleman and his team
are trying to capture an image

that shows its outline.

We're essentially looking
for the shadow,

or the silhouette,
of the black hole,

within this cloud of gas
that's swirling around it.

This technique
that we're exploiting

is the best hope I think we have

to actually image
a region of the universe

which has hitherto been
completely invisible to us.

Optical telescopes

can't see the black hole
directly.

But the glowing, super-heated
gas surrounding the black hole

sends out radio waves that can
be used to make an image.

Huge radio telescopes pick up
these signals from space.

The antenna will move
in azimuth and elevation.

This one, at the
M.I.T. Observatory near Boston,

is more than 100 feet wide.

It's big enough to detect
very faint radio emissions

from the black hole in our own
galaxy, 25,000 light-years away.

But it's not nearly big enough
to capture an image.

We need to take multiple copies
of these telescopes,

place them around the world

to create a virtual telescope
as large as the Earth itself.

Doeleman's team
will link up radio telescopes

around the globe,
from Hawaii to Chile to Africa.

When the whole network
is connected,

they'll have a virtual dish
over 10,000 miles across,

with 500 times the power
of a single telescope.

They think
it will be powerful enough

to take a picture
of the event horizon

of the supermassive black hole
at the center of the Milky Way.

They're already picking up
signals

from the dark heart
of our galaxy.

When we saw the first detection,

it was a moment where I just
looked at the computer screen

and said to myself,
"My God, we've done it.

We've actually seen something
that's so small

that it has to be coming from
right around the event horizon."

The signals are still too
weak to give a complete picture,

but Doeleman expects
the images to improve

as more telescopes come online
over the next few years.

Eventually, the outline of the
black hole itself should emerge.

But even a picture can't compare
to witnessing it for yourself.

In the distant future,
we may have the technology

to actually enter
and pass through a black hole

and maybe even
survive the journey.

Then we might finally answer
the question...

what lies
at the heart of a black hole?

Some scientists believe

we could use black holes
as a kind of portal,

with the potential
for travel across the universe.

This is still very speculative,

but the mathematics
seem to indicate

that as you fall
through a black hole

that you don't simply die...

you fall
right through a wormhole,

which is a gateway, a shortcut
through space and time.

Perhaps we could simply
rocket across the universe

through a subway system
that we call a black hole.

If black holes are
shortcuts through space and time,

it could turn one of the coolest
ideas from science fiction

into reality.

Time travel is possible,
but not very practical.

You see, the energy source,
the material that you need

to keep the throat
of a wormhole open

is something so ex otic

that we cannot produce it
in the laboratory.

But if you could,
it might be possible

to exploit the power of
black holes to visit yesterday.

Perhaps our descendants
in the future

have already mastered
this technology.

So one day,
if somebody knocks on your door

and claims to be

your great-great-great-great-
great-great granddaughter,

don't slam the door.

Black holes might even
be gateways to other universes.

On the other side
of a black hole,

there could even be...
a Big Bang.

As a black hole collapses
and matter falls into it,

perhaps the matter is blown out
the other side in a white hole.

Doesn't that sound
like the Big Bang?

If a Big Bang is just
the flip side of a black hole,

this could be
how our own universe was born.

If you look at the equations
for a black hole

and put in the parameters
of the universe...

the mass of the universe,
the size of the universe...

bingo!

You find that our universe

actually solves the equations
for a black hole.

In other words, we could be
inside an event horizon.

Perhaps we are actually living
inside a black hole.

Every black hole
might be the origin

of an entirely separate
universe.

If that's true,

there could be billions
of universes out there...

...each one
full of stars, planets, life.

Whatever we figure out later,

we know now
that black holes are everywhere.

They're bigger in size

and more critical
to the evolution of the universe

than we ever imagined.

Literally, our understanding

of the universe
that's important around us,

the universe
that's visible to telescopes,

has been profoundly affected

by our realization
that black holes are everywhere.

Once upon a time,

people thought
that black-hole physics

was too fantastic to be true.

And now they are center-stage.

We now know they dominate

the evolution
of the universe itself.

When I was a kid,

black holes basically played
a part in science fiction.

It was always
something to avoid.

Your spaceship...

you try to get around them
before you get drawn in.

But what we've learned
since then

is that black holes
play a huge role

and a huge number of roles
in the universe.

It's not an exaggeration to say

that if black holes did not
exist, we wouldn't be here.

We literally owe
our existence to black holes.

The story's not over yet.

There's still
much more to be discovered

about the mysterious objects
called black holes...

The masters of the universe.

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