All language subtitles for Universe 04.eng

I can see everything quite clearly.

It has a stark beauty all its own.

Magnificent desolation.

- Beautiful view.
- 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'd 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 prisons from
which even light itself can't escape.

But 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.

And we copy
at 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 14, 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,

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.

Twenty 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 burnt blue in 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 matters so densely
it tears a hole in the universe.

In the vicinity of a black hole,

space and time behave
in very counter-intuitive ways.

In fact, this river provides a beautiful
and surprisingly accurate analogy.

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 can imagine
I can 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 spacetime.

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

stars, and planets, and galaxies,

curve and distort
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.

And fortunately, 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 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 disk...

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 gluttonous period

that marked 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.

I mean, 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 1,000 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's 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.

I mean, imagine if there was
some giant star

that had formed close by
that 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
at 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?

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.

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 spacetime.

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 of physics in it.

This thing here,
"h-bar", is Planck's constant,

that's to do with quantum mechanics,
the subatomic world.

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, 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 sometime

"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 100 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?

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*,

of 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 is evaporated away,
about half of it is 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
spacetime 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.

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.

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.

We have a go
for engine start.

We have booster ignition,
lift-off of Columbia.

You just see fire.

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

Columbia now has burned
more than two million pounds of fuel

and weighs half
of what it did at launch.

Its huge. Chandra is about
the size of a school bus.

It's the largest telescope to ever
be launched by the space shuttle.

SRB 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 engine's
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,

then, 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, 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 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,

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

And then, the corpse of that star,

this sort of spaghetti-fied 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, it 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 dataset
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.