All language subtitles for Universe-004

NEIL ARMSTRONG: I can see
everything quite clearly.

It has a stark beauty all its own.

EXPLOSION

MUSIC: Neptune
by Foals

BUZZ ALDRIN: Magnificent desolation.

Beautiful! Beautiful!
Isn't that something?

The Milky Way seems
a tranquil place.

Hundreds of billions of stars

serenely spinning
through the cosmos.

But journey inwards
through the gas and dust

that shrouds the galactic core...

..and you see a curious sight.

Stars orbiting seemingly
empty space.

Something dark and ancient
lives here.

A hole in the fabric
of the universe.

Every one of those points
of light in the night sky

is a strange and fascinating place.

Magnificent suns with countless
planets orbiting around them.

Alien worlds beyond imagination.

But the strangest and most
fascinating places out there by far

are dark and unseen.

An invisible monster is lurking
in the centre of the Milky Way.

A monster that drains the colour
from the universe.

With the power to destroy worlds.

And stop time.

We've named the monster
Sagittarius A*

and we believe it to be
a black hole.

Sagittarius A* has played
a major role in the evolution

of our galaxy
and may even have influenced

the formation of stars
and planets like ours.

But there is so much more, because
black holes like Sagittarius A*

present the most profound
intellectual challenge.

They are part of nature
just like you and me,

so we should be able
to understand them,

but they are holes in the fabric
of the universe.

They are gravitational prisms
from which even light itself

can't escape.

And in trying to understand them,
physicists have been led

to completely reassess our most
basic understanding of reality.

But there are answers
hiding in the void

for those brave enough to seek them.

EXPLOSION

STEPHEN HAWKING: It is said
that fact is sometimes

stranger than fiction,
and nowhere is that more true

than in the case of black holes.

Black holes are stranger
than anything dreamed up

by science fiction writer,

but they are firmly matters
of science fact.

EILEEN COLLINS: And we copy.
Go for deploy.

You look out and this thing
is so big,

you certainly know that it's moving
over the head of the shuttle.

In the summer of 1999,
Nasa's flagship mission

for X-ray astronomy was released
from the shuttle cargo bay.

There is nothing as beautiful
as Chandra sailing off

on its way to work.

High above the Earth,
Chandra scanned the sky...

..hunting for some of the hottest
regions in the universe.

Exploding stars
and clusters of galaxies.

But on September 14th, 2013,

after 14 years, Chandra chanced
on something else entirely.

The telescope gazed into the
constellation of Sagittarius,

hoping to observe a large cloud
of hot gas.

Instead, it recorded a flash of
X-rays just a few pixels across...

..coming from the apparently
empty space in the galactic core.

Something had got very hot
for a very short period of time.

It's thought that the flash
seen by Chandra

may have been an asteroid
tens of kilometres across.

RUMBLING

Ripped apart and burning up
in a fireball

300 times brighter than the Sun.

The culprit?

Sagittarius A*.

The asteroid's destruction
was our galaxy's black hole

signalling its presence
to the world.

20 years ago, we didn't know for
sure that there is a black hole

at the centre of our galaxy,
but by measuring bursts of radiation

and observing in detail
the orbits of stars

close to the galactic centre,

we now know that Sagittarius A*
definitely exists

and we've been able
to measure its mass.

It is around four million times
the mass of our sun,

which makes it
a supermassive black hole,

one of the strangest and most
powerful objects in the universe.

And we've begun to suspect
that Sagittarius A*

isn't just some strange thing
that sits tens of thousands

of light years from Earth
at the centre of the galaxy.

It has played a crucial role
in the evolution of the Milky Way

and the whole story began with
the death of one massive star.

Soon after the dawn of time...

..the cosmos was home
to colossal stars...

..hundreds of times more massive
than the Sun.

Stars that burned blue
with intense heat.

But the brightest stars
are the shortest lived.

One lived a particularly
fast and furious life...

..burning through its nuclear fuel
in just a few million years.

And with nothing left in the tank,

gravity took over.

The star collapsed...

..ever smaller...

..ever denser...

..until it seemingly disappeared.

The remnants of the star,

now smaller than an atom,

lost from the universe.

All that's left is a ghost.

A black hole.

The genesis of Sagittarius A*
wasn't some bizarre one-off event.

It's possible that almost
all early stars

became black holes when they died.

Black holes are simply what happens
when gravity goes unchecked,

compacting matter so densely

it tears a hole in the universe.

In the vicinity of a black hole,
space and time behave

in very counterintuitive ways.

And in fact, this river
provides a beautiful

and surprisingly accurate analogy.

You see, close to a black hole,
you can think of space itself

as flowing towards the black hole.

Now, here, the flow is not too fast,

and so you could imagine
I could jump into that river,

I can swim faster
than the river of space,

and so I can escape
out into the galaxy.

But as you get closer
to the black hole,

the river of space flows faster
and faster and faster.

A collapsed star is so small
and yet so massive

that close to it, the gravitational
forces become overwhelming.

There is no limit to the speed at
which the river of space can flow.

There's a place where the river
becomes a waterfall,

where no matter how fast I swim,
I could never escape upstream,

and that's what happens
in the vicinity of a black hole.

The river of space flows at and
then faster than the speed of light.

Light itself can't move
fast enough to escape.

And that's what Sagittarius A* is.

It's a waterfall in the fabric
of the universe.

From the moment
the black hole formed,

the seed of Sagittarius A*
had a heart of pure darkness.

The interior forever hidden
from view.

Shielded from the rest of the
universe by a boundary in space.

The event horizon.

The ultimate point of no return.

As we approach the event horizon,

we get our first glimpse of
the true weirdness of black holes.

Einstein taught us that space
and time are not what they seem.

They are merged together
into a kind of a fabric -

- the fabric of the universe.
It's called space time.

And Einstein also taught us that
the presence of massive objects -

stars and planets and galaxies -
curved and distorts

the fabric of the universe.

And that's what we feel
as the force of gravity.

But that distortion is not only
in space, it's also in time.

As you go closer and closer
to a massive object,

the rate that time passes
slows down.

So if I look towards a black hole,

I see time passing slower
and slower and slower

until, on the event horizon,

time stops.

Sagittarius A* was born
a waterfall

in the fabric of the universe...

..where space flows faster
than light

and time grinds to a halt.

But our black hole was still
just a baby...

..dwarfed by the stars around it.

It was nothing like the monster
it would become.

Sagittarius A* today

is four million times the mass
of the Sun.

There has never been a star
that massive.

So it must have formed by the
collapse of something much smaller

and then it must have grown
over the lifetime of the Milky Way

by eating stuff.

Unfortunately, there has been a lot
of stuff around for it to eat.

The young black hole's
inexorable gravitational pull

meant there was no escape for
anything that strayed too close.

Sagittarius A* began to grow...

..pulling on nearby stars...

..before ripping them to shreds
and feasting on the hot plasma.

The black hole gaining more mass...

..and more gravitational power.

But we don't think there were
enough stars nearby

for the black hole to grow
supermassive

on a diet of stars alone.

Instead, it developed a taste
for more massive prey.

When another black hole passed
close to Sagittarius A*,

they became locked
in a gravitational embrace...

..spiralling towards each other,
approaching half the speed of light.

Before colliding.

Sagittarius A* cannibalised
its cousin...

..creating ripples in the fabric
of the universe itself.

More meals were to follow.

Black holes, stars, gas clouds -

whatever ventured too deep
into its lair.

And as our black hole's power
and influence grew...

..its surroundings
were changing, too.

Around the galactic core,

hundreds of billions of stars
were in orbit...

..slowly spinning around
their common centre of mass...

..evolving into the familiar
spiralling disc...

..the majestic Milky Way...

..with Sagittarius A* at its core.

Sagittarius A* became what we now
call a supermassive black hole,

many tens or even hundreds of
thousands of times more massive

than any star in the universe.

And Sagittarius A* is not unique.

We now think that virtually
every large galaxy

has a supermassive black hole
at its heart.

Chandra has looked beyond
the Milky Way

and observed countless supermassive
black holes lurking at the hearts

of the myriad galaxies
that litter the cosmos.

These monsters aren't obscure
quirks of nature.

They are fundamental features of it.

And far from being bit players,

we're starting to realise
that black holes

have the power and reach to sculpt
the galaxies around them.

The centre of our young galaxy
was rich in gas and dust.

More offerings to feast on.

This was a gluttons period

that marks a new era for the Milky
Way's supermassive black hole.

When the invisible monster
became sculptor of the galaxy.

Creation and destruction often
go hand-in-hand in the universe

and black holes are no exception.

Sagittarius A* is certainly not
only an agent of destruction

because the material that falls
inwards towards the black hole

doesn't all vanish
across the event horizon.

A lot of it goes into orbit
around the black hole.

And that region
is tremendously violent.

There are magnetic fields
that swirl around

and become twisted and distorted,
and they can throw material out

along the magnetic poles
of the black hole,

making jets that sweep
through the galaxy.

It's only recently that
we've grasped the true scale

of Sagittarius A*'s eruptions.

Engine start.

One, zero!

Lift off.

The Delta rocket carrying
a gamma-ray telescope

searching for unseen physics
in the stars of the galaxies.

Just over a decade ago, a completely
unexpected discovery was made,

likened to finding a brand-new
continent here on Earth.

The Fermi Space Telescope
was built to detect gamma-rays,

the most energetic radiation
in the universe.

As Fermi orbited the Earth,
it constructed a map of the sky...

..and saw, emerging from the plane
of the Milky Way...

..two colossal bubbles of material,

each 25,000 light years across.

These bubbles are superheated gas.

If our eyes were sensitive
to the wavelengths of light

emitted by those bubbles,
they would span half the sky

as seen from here on Earth.

And they point back
to the centre of the galaxy.

It looks like their origin
is Sagittarius A*.

Think about that.

Sagittarius A* is big
but not big on a galactic scale.

It would fit comfortably
inside the orbit of Mercury

in our solar system.

Though our black hole is only
a fraction of the size

of the galaxy around it...

..it had become sculptor
of the Milky Way.

Every few million years,

the dense ring of material
circling our black hole...

..was accelerated by twisting
magnetic fields...

..into fiery jets
of superheated matter.

Jets so powerful they stripped
the atmospheres

from any planets in their path.

And radiation rendered
every Earth-like world

within a thousand light years
uninhabitable.

But such was the scale of
Sagittarius A*'s outbursts

that far, far out in the galaxy...

..destruction...

..turned to creation.

If you're looking for reasons why
life not only began here on Earth

but was able to prosper for the
almost four billion years it took

for it to evolve into the complex
living world that we see today,

then it might seem
a bit of a stretch

to point to a supermassive black
hole at the centre of our galaxy

and say that's one
of the reasons why.

But we're now beginning to suspect
that those great outpourings

of energy from Sagittarius A*
played a crucial role

in making this region of the galaxy
one in which life can flourish...

..because the hot gas ejected
by Sagittarius A*

had a calming effect on the galaxy.

Now, you might think that a hot
gas cloud would produce more stars,

but, in fact, the opposite is true,

because hot means that everything
is moving around very fast

and that makes it more difficult for
gravity to grab hold of everything

and collapse it to form stars.

So Sagittarius A* reduced
the number of stars

that formed in this region
of the galaxy.

And that's a good thing.

Imagine if there was some giant
star that had formed close by

the exploded in a supernova
explosion.

That would not be a good thing
if you're an amoeba

and you have designs one day
on evolving into Einstein.

So, Sagittarius A* turned what
is potentially a violent region

of our galaxy into a peaceful one.

The warm gases pushed out
by Sagittarius A*

slowed the rate of star formation.

And, around one small yellow star
in a quiet region

at the unfashionable end of the
outer spiral arms of the galaxy...

..four billion years of stability

made all the difference.

Now, of course, there are many
things that are necessary

for life to exist on a planet.

The list is unimaginably vast,
but I think it is interesting

that on that list there is the
presence of this strange object,

a black hole, Sagittarius A*,

tens of thousands
of light years away.

The centre of our galaxy.

Having cleared out much
of the gas, dust and stars

that once lay close by...

..there was little left to feast on.

Our black hole fell silent.

The enormous bubbles
spotted by Fermi...

..echoes of a glorious past.

Today, Sagittarius A*
is a sleeping giant...

..a brooding beast...

..operating on a slow simmer.

Sagittarius A*'s journey
from violent destroyer

to sculptor of the galaxy to the
sleeping giant that we see today

has been pieced together over the
last 20 years by observational data

from telescopes
such as Chandra and Fermi.

But there's a very big
difference indeed

between knowing how a black hole
interacts with its environment,

how it sculpts a galaxy,

and what it actually is
at a deep level.

What is it really like inside?

STEPHEN HAWKING: Black holes
challenge the most basic principle

about the
predictability of the universe

and the certainty of history.

Nothing can get out of a black hole,

or so it was thought.

It's by looking into the future
that we're beginning to explore

the deep mystery of black holes.

Dozens of stars orbit
around Sagittarius A*.

Some passing just a few billion
miles from the event horizon.

A hair's breadth on galactic
scales.

These flybys
could have fatal consequences.

Some of these stars will likely
have planets in orbit.

Planets that may stray too close
to the beast.

A moth to a flame.

Pulled from its parent star
towards the abyss.

If the planet survives its
journey inwards...

..and we could stand on its surface

and look out into the
universe beyond...

..we would see space and time
becoming increasingly distorted.

But eventually, tidal gravitational
forces become too strong.

Inexorably, the singularity awaits.

The end of time,

where all paths terminate.

Over trillions of years,
all the stars around Sagittarius A*

will gradually fade and die.

On more and more alien worlds,
the dawn will fail to come.

But our supermassive monster
will go on,

its secrets sealed away inside.

Seemingly forever.

We predict that one day black holes
will be all that remains

in the universe. The final Dark Age.

BIRD CAWS

If nothing can ever escape
from black holes, if Sagittarius A*

really is an eternal prison,
then this is the end

of the story of the universe.

Darkness littered with holes
in space time.

But we don't think this
is the end of the story.

We now believe that even
black holes die.

And their deaths come at the hands
of what might seem

an inconsequential detail discovered
almost five decades ago.

In 1975, Stephen Hawking
published a remarkable paper

in which he showed that black holes
are not completely black.

They glow faintly.
They have a temperature.

And here's his beautiful equation
for the temperature of a black hole.

And you can see that there's
something deep going on

because this has got all the physics
in it. With this thing here,

h-bar, it's Planck's constant and
that's to do with quantum mechanics,

a subatomic world.
C is the speed of light.

G is the strength of gravity.

This kB here is
Boltzmann's constant,

that's to do with temperature
and thermodynamics.

And this M here is the mass
of the black hole.

It's even got circles
because it's got a Pi in it.

Hawking's conclusion proved
to be irrefutable,

and the implications are huge.

If something has a temperature,
then it radiates.

That's why if you put your hand
near something that's hot,

you can feel it. And so
over timescales that are billions

and billions and billions and
billions of times longer

than the current age of
the universe,

Sagittarius A* will
eventually evaporate away.

Very gradually, the Hawking
radiation

will erode Sagittarius A*.

Smaller and smaller.

Until many trillions and trillions
of years into the future...

..in a final burst of light...

..our black hole will die.

And then there will be darkness.

For all eternity.

Now, you may say,
quite legitimately,

"Well, why do we care?

"Why does it matter if
black holes evaporate away

"some time in the far, far future
of the universe?

"There'll be nobody around to
see it."

But the discovery that black holes
evaporate raises what I think

is the most profound question in the
history of physics, certainly

over the last hundred years,
and that's no exaggeration.

See, what happens if I set
fire to this piece of paper?

With Stephen Hawking's equation
written on it, I cause it

to evaporate away.
Do I destroy everything?

Do I remove every piece
of information, including

the equation from the universe
when it burns away?

Well, the answer is no.

If I could collect every ash,
every molecule of gas that burns off

into the atmosphere, then in
principle I could reconstruct

the piece of paper and everything
it contains.

Every piece of information on
this piece of paper,

including Stephen Hawking's
equation.

But can that be true
for black holes?

The ultimate gravitational prisons?
These objects in the sky

from which even light itself
can't escape?

When they evaporate away,
do they return the information

about everything that ever
fell in back to the universe?

STEPHEN HAWKING: Black holes ain't
as black as they are painted.

They are not the eternal
prisons they were once thought.

Things can get out of a black hole,

both to the outside and possibly
to another universe.

So, if you feel you are in a
black hole, don't give up.

There's a way out.

If information somehow escapes
from Sagittarius A*

as it evaporates away,

the implication is profound.

Black holes aren't tombs.

They're gateways.

We now believe that anything
that falls into Sagittarius A*

will live on.

Not as a physical object,

but as information.

Escaping from the heart of darkness.

Encoded in the Hawking radiation
in the far future.

The memory of all those worlds
that fell into Sagittarius A*

over the entire history
of the Milky Way galaxy is somehow

written in the ashes of the
universe in the far future.

But the real treasure lies
in the explanation

of how the information gets out
from those eternal prisons.

Now, what I'm going to tell you is
going to sound absolutely bizarre.

It's going to sound like science
fiction, but here goes.

When the black hole has evaporated
away, about half of it has gone,

the interior becomes, in some sense,
the same place

as the distant Hawking radiation
that was emitted aeons ago

that's out there in the far reaches
of the universe.

It seems that space time wormholes
open up between the interior

of the black hole and those distant
parts of the universe,

and it's that that allows us to
read the information inside.

Now, that is supposed to sound
weird, and I should say that nobody

really agrees on the physical
picture of what's happening.

But what everybody agrees on is this
- the black holes

are telling us that our intuitive
picture of reality

of space and time is wrong.

The idea that this place
is close to this place

and that time ticks along is wrong.

There is a deeper picture of reality

in which space and time
do not exist.

Our attempt to answer a
seemingly simple question

about the fate of objects that
fall into black holes has led us

to a profound and quite
unsettling conclusion.

Space and time, concepts so
foundational to how we experience

the world, are not fundamental
properties of nature.

They emerge from a deeper reality

in which neither exist.

The thing about black holes

is that nobody
really understands them.

So don't worry if you don't
understand what I'm talking about

because I don't understand
what I'm talking about,

and nobody else does either.

We're still a long way from fully
comprehending the secrets

of black holes...

..but we are beginning
to lift the veil.

Far from being a mere cosmic
aberration,

Sagittarius A* is a part
of our history and of our future.

Our black hole not only
made us who we are today,

it's our teacher,

slowly revealing the deepest
mysteries of the universe.

Secrets sealed away for so long

inside a place beyond forever.

The moral of the story is this.

Understanding the book
of nature is hard,

and so the more of nature
we observe, the more chance we have

of finishing the book.

Now, the strangest objects in nature
by far are black holes,

and so I suppose it's not surprising
that by peering over the horizon

and into the darkness, we have
caught a glimpse of something

deeply hidden - the underlying
structure of reality itself.

So if we want to understand
the meaning of it all,

we can't restrict ourselves
to the intellectually safe confines

of our planet.

We have to look out there
to the universe beyond.

# Baby, you understand me now

# If sometimes you see that I'm mad

# But I'm just a soul
whose intentions are good

# Oh, Lord, please don't let me be
misunderstood... #

So of the seemingly endless zoo
of objects in our universe,

from clouds of gas to planets
to stars, galaxies, what have you,

black holes are probably one
of the most fundamentally important

singular class of objects
that we can study.

A place where the laws of physics
literally break down,

and we have theories, but we can't
really know what's happening.

So black holes present
this remarkable invitation

to physicists, mathematicians,
astronomers.

One of the best tools we have to
study these exotic phenomena

is the Chandra telescope.

Chandra's kind of like a black
hole hunter, finding them

near and far throughout the galaxy
and the universe.

Just a few minutes away from the
26th flight of the Shuttle Columbia

with a crew of five.

I think a night launch
is particularly exciting.

You have a go for start.

We have booster ignition
and liftoff of Columbia.

You just see fire.

It lights up the night sky
in the most beautiful way.

Columbia now has burned
more than 2 million pounds of fuel

and weighs half of what it
did at launch.

It's huge. Chandra is about the size
of a school bus.

It's the largest telescope to ever
be launched by the Space Shuttle.

SRV separation is confirmed.

You're stressed about the astronauts
on board that are literally risking

their lives to help us get
a better view of the universe.

When the main engines cut off, we're
in zero G.

We separate the tank
and we're orbiting the Earth.

And when we're sure that everyone
is ready at mission control

and I go ahead and pull the switch
marked deploy,

and you're looking at the deploy
of the Chandra X-ray Observatory.

Chandra is an X-ray telescope,

which means that it can see the most
energetic light

coming at us from the universe.

The telescope has to be
outside the Earth's atmosphere

because the Earth's atmosphere,

thankfully for us,
blocks out X-rays.

Otherwise, if...
We'd just get fried.

The Chandra satellite, by rising
above the atmosphere,

has a much clearer view.

Why is that so interesting for
studying things like black holes?

Black holes can excite matter
in their vicinity

to very high energies.

They can get atoms and parts
of atoms whipping around

and by revving up those particles
to very, very high energies,

they will radiate

so we can gather enormous amounts
of information

about the immediate vicinity
of a black hole.

When we look at Sagittarius A*
today,

it's quiet and not doing very much.

But when we look at other
supermassive black holes

in the universe, they're active.

So you can take Chandra and watch
a black hole have a small snack,

maybe like a human might have a
little biscuit in the afternoon,

and it's something like an asteroid

and there will be a small sort of
X-ray signature from that event.

But you can also see a black hole
have a really, really big snack,

and Chandra's may be able to witness
that as well.

Chandra has witnessed the
destruction of a star

by a black hole itself, right?

So this poor star wanders
in to the black hole

that it rips the star apart,
it shears it, right?

And then the corpse of that star,

this sort of spaghettified matter
that starts spiralling around

the event horizon lights up
in X-rays.

So to be witness to that, to observe
the destruction of a star,

you know, in time,
was just extraordinary.

It's just unbelievable.

There's this one pretty famous image
that Chandra took called

the Chandra Deep Field South,

and it's the deepest X-ray image
ever.

In that one data set,
there's thousands of black holes,

like maybe 5,000 of them,
if not more.

And it just kind of helps show you
that they're all over the place

and there's so much more
to discover.

Next time...

..we journey back
to the cosmic dark ages,

exploring a time before
the Big Bang...

..to answer the ultimate question.

How did the universe come to be?

Journey through the universe
with the Open University

and learn more about stars, planets
and galaxies with this free poster.

Order your poster by calling...

..or go to...

..and follow the links
to the Open University.

# I'm just a soul whose intentions
are good

# Oh, Lord, please don't let me be
me misunderstood

# Don't let me be misunderstood

# I try so hard, so please,
don't let me be misunderstood... #