Original subtitles

Neil Armstrong: I can see everything quite clear! Y.

It has a stark beauty all its own.

♪ See me when I float like a dove

♪ skies above...

B uzz a ld ri n: Magnificent desolation.

- Beautiful view. - Armstro n g: Isn't that something?

♪ Take me away ♪

Brian Cox: The milky way seems a tranquil place...

Hundreds of billions of stars serenely spinning through the cosmos.

But journey in wards 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 in visible 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 I

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 gra vita tional 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.

Eileen Collins: 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.

Cox: In the summer of 7999,

NASA's flagship mission for x -ra y astronomy

was released from the shuttle cargo bay.

Collins: There is nothing as beautiful

as chandra sailing off on its way to work.

Cox: 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 74, 2073,

after 74 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—ra ys, 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 "I

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'tjust

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...

E ver smaller, e ver 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'fi

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 in visible 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.

Man: Engine start.

One, zero. Lift-off.

The delta rocket carrying a gamma ray telescope,

searching for unseen physics in the stars of the galaxies.

Cox: Just over a decade ago,

a completely unexpected disco very 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 7,000 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?

Cox: 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 I

some passing just a few billion miles from the event horizon,

a hair's breadth on galactic scales.

These fl ybys could have fatal consequences.

Some of these stars will likely have planets in orbit,

planets that may stray too close to the beast,

A math 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.

Inexorabl y, 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.

5 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.

Ha wking'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 "I.

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.

Grant tremblay: 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 do wn.

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

David kaiser: 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.

Woman: Just a few minutes away

from the 26th flight of the shuttle, Columbia,

with a crew of five.

Kimberly arcan d: I think a night launch is particularly exciting.

Woman: We have a go for engine start.

We have booster ignition, lift-off of co lu m bia.

Arcan d: You just see fire.

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

Man: Colu m bia 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.

Man: 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—ra y 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.

Kaiser: 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 re wing 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.

Arcan d: 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.

Tremblay: 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.

Arcan d: There's this one pretty famous image that chandra took

called the chandra deep field-south, and it's the deepest x—ra y 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.