All language subtitles for How.The.Universe.Works.S09E11.Journey.To.A.Black.Hole.1080p.AMZN.WEB-DL.DDP2.0.H.264-alfaHD_track4_[eng]

NARRATOR: We're on a journey
to the heart

of the supermassive
black hole, M87 star.

Our mission, to investigate
one of the most mysterious places

in the universe.

PAUL: M87 is a great target
for us to visit,

because one, it's close,

and two, it's active,
it's feeding.

Supermassive black holes
are the engines

(SWOOSHING)
that power the universe.

Supermassive black holes
are a key factor

in the birth, life,
and eventual death of galaxies.

And the more we study them,
the more puzzling they become.

They're the master key
to most of the unsolved mysteries
in Physics.

The physics inside
a supermassive black hole

are beyond weird.

They are the final frontier
of our understanding.

Your imagination can run wild.

Maybe it's even the source
of other universes.

There's only one way to find out,

to go where no one has gone before

and journey to the heart

of M87 star.

(BOOMING)

We speed across M87...

..a gigantic galaxy 55 million
light-years from Earth.

At its heart
lies a supermassive black hole...

..M87 star.

(RADIO CHATTER)
It is the first and only black hole

ever photographed.

We want to find out
how M87 star grew so large,

what lies inside,
and how it controls the galaxy.

5,000 light-years out
from the supermassive black hole,

we get our first sign
of the danger ahead.

We see giant holes
carved out of the galaxy...

..starless voids
thousands of light-years wide.

As we approach, we can see

that wreckage littered
around the vicinity.

It's like entering the lair
of the dragon

and seeing the bones
of all the explorers

who came before you.

What cataclysmic force
tore these giant cavities

in the galactic gas clouds?

As we fly next to a brilliant shaft
of energy...

..thousands of light-years
from M87 star,

we get a clue.

It's a deadly stream of radiation
shooting out across the galaxy,

a jet.

This jet looks like a searchlight
or a beam from a lighthouse.

You're seeing
this monumental thing.

It's screaming out
of the black hole,

blasting out radiation.

(SONIC BEEP)

When I first saw a photo of a jet,
I was like, 'Whoa!'

Am I like, misreading the scale
of this image?

Cos there was this crazy Star Trek
like beam just coming out.

(SWOOSH)

In 1918, American astronomer
Heber Curtis

described the jets
as a curious straight ray.

A century later, observatory images
reveal they pulsate with energy.

PAUL: The images show knots
and clumps in these jets.

They show that
it's just not smooth and nice,

that there's been a history
of violence inside this jet.

This violent energy pushes
the knots along the beams.

The knots reveal
the speed of the jets.

(WHOOSHING)

It's like looking
at a fast-moving train.

Rail cars of the same colour
blur into one continuous image.

But different-coloured cars
stand out against the others.

It's the same with the knots
moving along the jets.

So we can figure out
how fast the jets are really moving

by looking at knots of material
coming out

from near the black hole.

When astronomers measured
the speed of two knots,

they got a big surprise.

One is moving at 2.4 times
the speed of light,

and the other is moving
over six times faster than light.

How could this possibly be?

As weird as the physics
around a black hole is,

that's not actually happening,
nor is it allowed to happen.

Nothing can actually go faster
than the speed of light,

so obviously,
we're missing something here.

The knots may seem
to break the speed of light,

but the universe
is just playing with us.

It's really just a consequence
of the fact

that a lot of this jet
is pointed toward us,

pointed partially
toward the observer on Earth.

That, in a sense,
is a sort of optical illusion

that tricks you into thinking
it's moving faster.

It's a simple trick of the light,

a bit like the way a spoon

in a glass of water looks bent
and distorted.

The impossibly fast speed of the jet

is just an illusion of perspective.

From our perspective,
it looks like the whole thing

is moving towards us
faster than light.

But really, it's just cruising
along very, very fast.

The jets aren't breaking the laws
of Physics.

They're pushing up against it.

They're going at 99.999995%
(SONIC HUMMING)

the speed of light.

Imagine the energies necessary

to accelerate this entire jet
to that speed.

So what could produce
enough energy to blast jets

across the galaxy at close
to the speed of light?

There is a clue far ahead.

The jets shoot out from a tiny,
brightly glowing object.

This is where things go nuts.
This is the centre of the action.

This is where the real stuff
happens.

A ring of superhot gas

and dust whirls around
the supermassive black hole.

It's called the accretion disk,

and it shines a billion times
brighter than the sun.

If you had a ringside seat
next to M87 star,

you would probably be fried
very, very fast.

(RUMBLING)

But if you were some magical being
and could survive anything,

and if you had,
you know, million SPF sunscreen

and really, really great sunglasses,
what you would see

is this enormously bright
vortex of gas

swirling this dark void.

This bright vortex spins around
the supermassive black hole,

at over two million miles an hour.

So there's a tremendous amount
of friction

as material moving slower and faster
rubs against each other.

That's what's heating the disk up,

and that's what's causing it
to glow.

Temperatures reach billions of degrees,

making this one of the hottest

and most electrically charged
environments in the whole universe.

This intense energy
lights up not just the disk

but also illuminates our path
across the galaxy.

So these super-massive black holes,

they're some
of the brightest objects.

They can outshine the light
of all the stars in an entire galaxy

by a factor of a thousand or more.

Such intense light clusters
were first detected

when we started to explore space
with radio telescopes in the 1960s.

PAUL: Decades ago,
astronomers began to see

these incredibly bright sources
in the deep sky

and they knew they were far away
and they knew they were bright.

It made them the brightest things
in the universe

and astronomers had no idea
what they were.

It wasn't until years
and years later

that we found that
these bright sources

were powered by giant black holes.

Scientists think
that the intense energy

of the accretion disk
is the source of the jets.

The hot, swirling gas and dust
produces powerful magnetic fields.

As the disk spins,

it twists up the magnetic fields
at the poles of the black hole.

Energy builds.

Finally, the magnetic fields
can't contain the energy any longer.

They snap and blast
the jets out into the galaxy.

Even many light-ears away
on the ship,

we can see
this violent release of energy.

It's like the universe's
biggest fireworks display.

Two jets streaking
out of M87 star's poles...

..one shooting away
into the distance,

the other racing past our ship.

We're at a safe distance.
Other things are not.

So when these jets shoot outward
from the supermassive black hole,

they don't shoot outward
into nothing.

If a jet hits a gas cloud,
it annihilates it.

It just punches a hole
right through it.

It's like a train
going down a snowy track, right?

The gas is like the snow

and the jets are like this freight
train ploughing across it.

But here, a freight train travelling
at close to the speed of light...

..smashing into clouds of gas...

..lighting our way to M87 star...

..as we follow the trail
of destruction.

There is evidence of similar
destruction across the universe.

In the Cygnus A galaxy,
supermassive black hole jets

have caused damage
on a colossal scale.

In many ways, Cygnus A
is like a cosmic shooting gallery.

You see this crime scene,
this beautiful mess.

HAKEEM: So when this jet comes
out of the nucleus of Cygnus A,

it's gonna encounter gas clouds.

At that point, shockwaves set up,

and this jet just rips
right through this material,

sending shock waves
in every direction,

creating absolute chaos.

It's hard to believe
how much devastation
these jets can cause,

they're punching a hole in the gas
100,000 light-years wide.

I mean, that's...that's the scale
of an entire galaxy.

In 2020, more carnage was discovered

in a galaxy 390 million light
years away.

The Ophiuchus galaxy cluster
is a collection

of a huge number of galaxies
all orbiting each other,

held together by their own gravity
and when astronomers looked at it,

they saw something
they didn't understand.

It looked like a wall of gas there.

At first, we didn't know the cause.

Now,
we know it was a powerful jet...

..hitting a huge cloud of gas.

The super-massive black hole
in the galaxy

in the centre of this cluster
is blasting out material

that has carved a cavity well over
a million light years across.

This is a vast hole in the gas.

Shockwaves from the jet hit the gas,
triggering a monstrous explosion,

which carved out a cosmic void

15 times the size
of the Milky Way.

The wind from this black hole
has swept up that material

like a snowplough pushing snow.

That's what's causing that wall
that the astronomers saw

and the amount of energy this takes
is huge.

It's 800 billion, billion times,

the sun's energy that it will emit

over its entire
12-billion-year lifetime.

As we head towards the centre
of the M87 galaxy,

we enter hostile territory.

The closer to the supermassive
black hole we travel,

the more dangerous it gets.

As we approach the central core
of M87, we start to feel it.

But all this energy,
all this ferociousness,

is powered by that black hole.

Intense winds start
to buffet the ship.

They push away vital gas,
quenching star birth.

Could these winds
end up killing the galaxy

and M87 star itself?

NARRATOR: We're on a mission
to explore

the supermassive black hole
M87 star.

First, we have to cross
the M87 galaxy.

It's 120,000 light-years across,

and it looks like a giant puffball.

M87 is an absolute monster.

It's a giant, elliptical galaxy,

and that means that, as you go
from the edges to the interior,

you see a higher and higher
density of stars.

This vast galaxy contains
several trillion stars.

What's strange is that almost
all of them are the same colour.

So as you see, you are...
Your sky is covered

with countless red points of light
everywhere you look.

Most of these points of light
are small,

long living-stars called red dwarfs.

So what happened
to the different-coloured stars

that we see in other galaxies?

When you create lots of stars,
you make lots of blue and red stars.

But the blue ones
don't last very long.
They explode and are gone.

The red ones,
the ones that are lower mass,

those are the ones that live
for many, many billions of years.

M87 hasn't made stars in so long
that its stars are mostly red.

We call galaxies
with mainly red stars,

red and dead.

So the only stars
that are left in these red

and dead galaxies are billions
of year-old populations.

And since
it's not making new stars,

err, the clock is ticking on M87.

Essentially,
it's a dead galaxy walking.

The M87 galaxy hasn't made
any new stars for billions of years.

Something had to make that happen.

Something had to deplete or heat up

or push away the gas
in those galaxies

that would otherwise go
into forming stars.

We think that black holes

in the centres of galaxies
are the ultimate answer to this.

So how did M87 star kill off

star formation billions
of years ago?

As we cruise towards
the supermassive black hole,

we get a clue from the strong winds
buffeting the ship.

So these winds can be
incredibly powerful

and really, really fast, right?

You think a hurricane
on Earth is bad?

You should see some of these winds.

Space wind is very different
from wind on Earth.

Earth winds are moving air.

When the Sun heats a surface
on our planet,

the air above warms and rises.

Cool air below fills the space
left by the rising warm air,

creating winds.

In space, winds were made up of gas
and superheated plasma.

The power that generates
the winds lies ahead

the bright accretion disk
surrounding M87 star.

Because it's so incredibly hot,

it liberates
an enormous amount of light,

and that light can drive a wind,

and so black holes can power winds.

They power winds with light itself.

And the more material that's falling
into that accretion disk,

the bigger and hotter it gets,

and the more powerful the wind
is that the black hole blows.

We understand that light
from the accretion disk

creates the winds,
but that is about all we know.

We don't know
that much about the wind.

Is it expanding in all directions
like a sphere?

Or is it aimed in jets, very narrow

and only moving
in two different directions?

Measuring the effect of the winds
isn't as easy as you might think.

It's not like going outside
on a windy day
and doing one of these.

You have to infer
what's going on with the winds

by studying the light emanating
from this object.

We wanted to find out
if black hole winds

expand like a bubble
or travel in narrow streams.

So we studied how iron dust
from the accretion disk

blocks the light driving the wind.

Astronomers found the answer
when they looked

in the X-ray light spectrum.

And what they detected
was iron absorbing those X-rays

in every direction they looked
around the black hole.

That's only possible
if the black hole

is blowing out a wind
in every direction,

which means that
it is definitely blowing out

a spherical wind, which is expanding
into that galaxy.

And so these black holes
can almost literally inflate

this growing sphere bubble of gas

that's outward flowing (CRACKLING)
from the heart of the galaxy.

These winds push out

throughout the entire galaxy of M87,

transporting heat

and energy throughout
the entire volume of the galaxy.

What we found is that
it's expanding away

from the black hole at a quarter
of the speed of light,

40,000 miles per second.

(SWOOSHING)

And for the M87 galaxy,
that is bad news,

because hot, powerful winds

kill off star birth.
(WHOOSHING)

The winds can push away the gas

that would have normally
formed stars

so they can effectively quench
star formation in a galaxy,

causing it to gradually die.

And, it gets worse.

In order for a galaxy
to produce stars,

it needs lots of gas and dust,

and that gas and dust
needs to be incredibly cold.

Hot winds from the black hole
heat up gas clouds

so they can't collapse into stars.

As M87 star has grown,

it has slowly shut down
star formation.

As the black hole
in the centre of the galaxy grows,

it has stronger and stronger winds,

and this means it's gonna drive out
more and more matter.

And that's what makes it a galaxy

that can no longer support
star formation.

So a supermassive black hole
can determine

the star formation happening
in the galaxy.

It can help to regulate
the amount of gas in the galaxy

and therefore the number of stars
that are formed in a galaxy.

Although, M87 star is tiny compared
to the vast galaxy around it,

it still controls its host.

When you compare it to the size
of the galaxy it's sitting in,

it's like comparing a grape
to the size of the Earth.

So to think that something
so relatively small compared
to the galaxy

could have such a profound effect

over effectively
all of cosmic history,

is just this
remarkable illustration

of how energetic
a black hole can be.

In the relationship between
a supermassive black hole

and the material surrounding it,
the black hole is in charge.

But not all super massive
black holes kill off star formation.

The Phoenix Cluster
contains a super-massive black hole

but produces enough cold gas
to form 500 stars a year.

This is a place where we normally
expect to only see hot gas.

Here's the mystery:
Why is all of this cold gas

so far out in the galaxy?

Observations revealed that jets
shooting out

of the super-massive black hole
inflate giant gas bubbles

82,000 light years
through the galaxy.

When the team superimpose
a map of the cold gas

over a map of the hot bubbles,
they line up.

There's something about
those hot bubbles

that are allowing this cold gas

to be created kind of trooped
on top of it.

When the jets move out
and inflate the bubbles,

they drag behind a wake
of slightly cooler gas.

This colder gas
starts to form more stars.

So the black hole
can redistribute gas

and it can heat up gas
and it can also cool down gas.

And so that way
it can regulate the environment

inside of the galaxy.

Although, M87 star calls the shots,

its past, present, and future

are inextricably linked
to its host galaxy.

The view from our ship
is endless space,

calm and unchanging.

But the M87 galaxy
has a violent past...

..a history of cannibalism,

death, and destruction.

(BEEPS)

We've travelled
thousands of light-years

across the M87 galaxy,

but its supermassive black hole
is still far in the distance.

From our current position,
M87 star may look small,

but it's 6.5 billion times
the mass of the sun.

So how did it get so big?

One big mystery that
we're still trying to understand

is what controls
how big the giant black holes

at the centres of galaxies become.

And we know that
it's tightly correlated

with things like
how big the galaxy is.

Bigger galaxies
have bigger black holes.

To understand how M87 star
became so big,

we have to investigate the history
of its galaxy.

We need to discover
how M87 star's host galaxy

grew so large.

M87 is huge.

It's a big galaxy
with a big black hole.

GRANT: It's really, really big.

It's what we call
brightest cluster galaxy,

and these so-called brightest
cluster galaxies

are amongst the most massive
galaxies in the known universe.

Usually, a galaxy with the mass
of M87 is much smaller,

but M87 is puffed up hugely.
Why?

One lead comes from the layout
of M87's stars.

As we travel through the galaxy,

we see that the stars spread out

over an area 100 times larger
than expected.

So, what scattered the stars?

Galaxies aren't static,
every galaxy is moving,

and sometimes galaxies
get very close

and can interact with each other.

Interact is a polite way

of describing something
extremely brutal.

Galaxies are colliding
with other galaxies,

they're cannibalising
smaller galaxies

or tearing each other apart.

Sometimes they're like drive-bys,

and they'll warp
each other's structures.

Sometimes the galaxies have
head-on collisions and merge.

Merging pulls in new gas
and stars...

..so galaxies grow larger.

Galactic cannibalism is common.

Maybe the M87 galaxy
ate its neighbours.

But how can we find out?

We could try to identify stars

that came
from the consumed galaxies...

..but that's not straightforward.

When you're trying to map out
a distant galaxy,

it turns out using their stars
is a really hard thing to do.

They smear in with the foreground
and the background.

It's very difficult
to see any evidence

that that galaxy merger
ever happened.
It's all smoothed out.

It's kind of like throwing
a bucket of water into a pond.

And then asking
after the waves go away

to separate
which molecules of water

came from the pail of water
versus which were in the pond.

All you see
is just mixed pile of water,

uh, and it's similar to that
with the stars in a galaxy.

So how can you spot water
from the bucket in the pond water?

We need to detect signs
of disruption,

like ripples or distinct streaks
of sand and mud

thrown up by the disturbance.

When galaxies merge, they may also
leave a leftover that stands out...

..like a planetary nebula.

Planetary nebulae
are these bright beacons
that you can pick out

and map out the galaxy
with great precision.

A planetary nebula forms
when a dying,

mid-sized star blows off
its outer layers

after running out of fuel.

These outer layers of gas expand,
forming a nebula,

often in the shape of a ring
or bubble.

And you see this beautiful,
glowing blue-green blob

coming away from the star,
these are so much bigger
than stars.

You can pick them out very easily.

One team went planetary nebula
hunting in the M87 galaxy.

As they mapped the galaxy,

they picked out 300 distinct
glowing points.

The points are blue-green,

confirming they're planetary nebulas.

Planetary nebulae are great.

They really stand out like needles
in a planetary haystack.

The nebula's movements are distinct
from the stars in M87.

This shows they formed in a smaller,
younger galaxy, not M87.

Because we see these planetary nebulae,

something must have happened
in this old, dead galaxy.

What was it? A galaxy collision.

The discovery
of the planetary nebulas

shows that at some point
in the last billion years,

M87 ate a smaller galaxy.

This galaxy strayed too close
to the much larger M87.

M87's powerful gravity
snared the smaller galaxy

and dragged it closer and closer.

You could see
this galaxy getting bigger

and bigger and bigger in the sky,
and it wouldn't stay the same shape.

As the galaxy got closer,
it would begin to distort,

and your galaxy
would distort, as well,

until the sky was filled
with rivers of stars.

M87 pulled in the small galaxy
and swallowed it whole.

Can you think of anything
more dramatic

than the collision of two galaxies?

A violent history
of mergers explains

how the M87 galaxy grew so large.

Each event brought in
many millions of stars.

The collisions also unleashed
enormous gravitational forces...

..scattering the stars
like confetti.

After a collision like this,

the stars are probably
ten to 100 times

more spread out
than they were before.

Some collisions threw stars around.

Others changed the shape
of the entire galaxy.

If that galaxy merger
is violent enough,

it injects so much energy
into the galaxy

that the stars basically
all move away from the centre,

and it makes the galaxy
much more puffy.

Gradually transforming it
into the smooth, featureless,

elliptical shape.

Most galaxies
have a supermassive black hole
at their centre,

including those galaxies
eaten by M87.

So, what happened
to those black holes?

Did they merge with M87 star,
increasing its size?

M87, the fact that
it's an elliptical galaxy

also supports the fact that
it's had multiple supermassive
black hole mergers,

which is how M87 star could have
gained its sizeable mass.

Compared to its violent history,

the M87 galaxy
is now relatively calm.

We think that in the past,

M87 star grew by gobbling up
other supermassive black holes

brought in by collisions
with other galaxies.

But we don't really know,

because physics suggests
that supermassive black holes

can never merge.

Instead, they lock together
in a cosmic dance for eternity.

As we travel closer
to the supermassive black hole,

we pass the remnants
of smaller galaxies

eaten over the last
10 billion years.

They reveal how the M87 galaxy
got so vast.

Most of these consumed galaxies

probably had a supermassive
black hole of their own.

If M87 got so large
by eating galaxies,

did M87 star get supermassive

by consuming other
supermassive black holes?

So when galaxies merge,

all their stars
and nebulae mix together,

and then also there supermassive
black holes

eventually find each other
and find their way

down to the centre
of the newly merged galaxy.

Just like dropping
two stones into a pond,

they'll both reach the bottom,
they'll both move toward the centre,

and they will start to move
ever closer together.

But do the supermassive black holes
actually collide?

We've witnessed
the merging of smaller,

stellar mass black holes,

and we've seen supermassive
black holes get close together,

but we've never observed them merge.

When galaxies merge, their central,

supermassive black holes
should merge.

The first step
in the merger process,

they're sinking toward the centre
of this newly formed galaxy.

As they plunge
towards the galactic centre,

the supermassive black holes
plough through fields of stars

and clouds of gas.

They don't just run
into each other,

they inspiral toward each other,

so they're gonna
scatter stars everywhere,

and the closer they get,

the more rapidly
they will orbit each other.

So things get even more
and more chaotic and crazy.

In all the chaos,
something strange happens.

The supermassive black holes
stop moving closer to each other.

This is a problem, and we call
this the final parsec problem.

So what's going on?
Why do they stall?

The final parsec problem happens
when two supermassive black holes

run out of material
to help them to merge.

If there's not enough stars or gas

that the black holes
can interact with,

it takes longer than the age
of the universe

for them to lose enough energy
to merge.

And so the black holes
effectively stall

at this final parsec of separation.

The two supermassive black holes
lock together

in an eternal cosmic dance...

..close but forever apart.

But some supermassive black holes
must have merged.

It's highly likely that
many of the galaxies M87 swallowed

had supermassive black holes.

And yet, on our trip,

we haven't seen
lots of supermassive black holes,

just one, M87 star.

So mergers take place, but how?

In 2019, we got a clue

from a galaxy called NGC 6240.

This particular galaxy

looks like the aftermath
of a massive galactic collision.

There are lumps
and clumps of stars,

random groups at random directions
and random velocities.

It's all mixed up,
which is what we think

galaxies look like
after a massive merger.

The merger aftermath reveals
a more complex series of events

than a two-galaxy collision.

What we find in the centre
of this galaxy isn't two,

but three giant black holes,

which suggests that
there have been three galaxies

colliding in recent history.

So when this new galaxy
starts to merge

with the galaxy
that hosts the stalled pair,

it brings in its own third
supermassive black hole.

Now this supermassive black hole
perturbs the system,

and it makes what's at the centre
highly unstable.

The gravity of this third
supermassive black hole

steals orbital energy
from the stalled pair,

pushing them closer together.

It's almost a thief that comes in

and takes away
some of that rotational energy

from this binary black hole system.

As the two supermassive black holes
lose orbital energy,

they finally come together.

The likeliest thing to happen
is that the least massive

supermassive black hole is ejected.

And the remaining
two merge very quickly.

The high-speed merger
will last just milliseconds,

but it will trigger...
(WHOOSHING) (SONIC BOOM)

a gigantic explosion.

When these giant black holes merge,

more energy is released
in this process

than our entire galaxy will emit

over the course of billions
of years.

Perhaps, M87 star merged

with other supermassive black holes
in the same way.

A third black hole, helping it

to overcome the final parsec
problem.

It's possible that mergers
with other supermassive black holes

allowed M87
to reach its sizeable mass

of six in a half billion
solar masses.

Supermassive black holes
meet their match

when they square off
against each other.

The fallout is cataclysmic,

and as we get closer to M87 star,

our mission becomes more dangerous.

We enter the gravitational kill zone

surrounding the supermassive black hole.

We know the dangers.

Any unwitting stars
that get too close

are stretched, shredded,

and torn apart,
creating one of the biggest

and brightest light shows
in the universe.

But their death may solve
one of the mysteries

of supermassive black holes.

How fast they spin.

It's difficult to calculate just
how fast a featureless black object

hidden by a bright disc rotates.

You need a lot of patience
and a little bit of luck.

Astronomy is sometimes
a pretty opportunistic science.

You have to be looking
at the right place
at the right time

to figure out something new that
we've never seen before.

Recently, astronomers caught a break

when they spotted
an extremely bright flare

in galaxy PGC 043234.

It was hard to miss.

The flare was 100 billion times
brighter than the sun.

And the energy output
was absolutely ridiculous.

If this happened in the centre
of our galaxy,

it would have been so bright,
we could see it during the daytime.

A routine search for supernovas,

violent deaths of giant stars
detected the intense flash.

ASAS-SN is this network
of telescopes

designed to look for brief,

high-energy events
all around the sky,

and primarily supernova.

They saw a bright flash,

and they thought,
'Oh, yay, another supernova.'

If you see
a bright flash of light

coming from a galaxy,
that's kind of your first thought.

But it didn't look like
a supernova at all.

It didn't act like (BOOM)
a supernova flash would.

It didn't have
the right characteristics.

It wasn't behaving
like a typical supernova.

It had to be something else.

So they send out an alert
to the astronomical community,

saying, 'Hey,
there's something cool happening

in this region of space.'

Once an event is flagged as real,

then what happens
is other telescopes

turn their attention to that event.

The data revealed something strange.

After the initial flash,

there are still smaller flashes
that repeat,

and if you're gonna kill a star
in a supernova,

there's nothing left
to repeat like that.

(EXPLODES)

Intriguingly, it flashed on and off
about once every 130 seconds.

The flashes continued for 450 days.

When astronomers
looked at this galaxy in detail,

they saw that this event happened
right at the centre,

and there's a black hole there
with about one million times

the sun's mass, and that was...

"That's it, man.
That's the smoking gun."

What they observed
was an extremely rare phenomenon,

a tidal disruption event.

Catching one live as it happens
is an astronomer's dream.

This was our first time
catching a black hole

in the act of feeding on a star.

In galaxy PGC 043234,

a star wandered too close
to a supermassive black hole.

As this unfortunate star
got close to the black hole,

the black hole is spinning,

and the gravity around
this monster black hole
is so strong

that it could pull the star apart.

The side of the star
closer to the black hole

is feeling a much, much stronger

gravitational pull
toward the black hole

than the far side of the star
because it's farther away.

And what this does is
it stretches the star.

So it got ripped to shreds,
it got shredded.

It got pulled out and stretched
and whipped around the black hole.

And this stretches the star
into some giant long arm,

and that swirls around
and is trapped

as it orbits the black hole.

The accretion disk
snares the shredded star.

And what this means is that,

that accretion disk
is gonna increase

its output of radiation,
in particular,
high-energy radiation.

As the star embeds
in the accretion disk,

a massive flare of radiation erupts,
lighting up the universe.

After this initial burst,

the spinning star debris sends out
a continuous stream of light.

Our telescopes only pick up
this radiation

on each rotation of the disk.

It's like seeing the beam
from a lighthouse every 130 seconds.

The flashes are the final pulses
of a dying star...

..and those flashes
reveal both the width

and the rotation speed
of the supermassive black hole.

We learned that
the central massive black hole

is about 300 times wider
than the Earth,

but it's rotating
every two minutes.

It's rotating
at half the speed of light.

(WHOOSHING) That's over
300 million miles an hour.

We don't yet know
how fast M87 star is spinning,

but we do know the accretion disk

rotates it over two million miles
an hour.

This glowing ring,
hundreds of light-years wide,

now lies directly ahead of our ship.

It is one of the most awe-inspiring
and deadly places in the universe,

and we are heading straight for it.

NARRATOR: After our long trek
across the galaxy,

we finally face the mighty
supermassive black hole

at its centre, M87 star.

A dazzling glare confronts us.

This is the accretion disk,

a ring of hot gas and dust spinning
at over two million miles an hour.

M87 star's accretion disk
is so bright,

the Event Horizon Telescope
photographed it from Earth

55 million light-years away.

I remember where I was
when that image was released.

I was with my colleagues
at the Centre for Astrophysics,

and we were all watching
the press conference live

and just absolutely slack-jawed
when that image hit the screen.

HAKEEM: I was sitting in the airport
when I saw this black hole image,

about to take a flight to New York.

I got so excited

that I actually walked away
from my backpack sitting there.

Seeing that picture, it really
doesn't leave room for doubt.

Black holes are real.

The Event Horizon Telescope photo

is the first picture ever taken
of a black hole.

The image revealed M87 star
spins in a clockwise direction,

and it's 23.6 billion miles wide.

That's around three million Earths
lined up in a row.

The photo also confirmed
M87 star's membership

in a very exclusive club,

The 1% of supermassive black holes
that actively feed.

The image
from the Event Horizon Telescope

tells us that M87 is indeed

actively growing and accreting
and eating material around it.

It shows gas swirling
around that black hole

on its way to being swallowed.

But do all supermassive
black holes consume material

in the same way
that M87 star does?

Is it possible,
different black holes
have different table manners?

Well, it turns out
that's really true.

Some are more delicate eaters.

In 2018, we discovered
a supermassive black hole

250 million light-years from Earth
that eats on a schedule.

Now we have this case
of a black hole

that looks like
it's feeding three times a day.

It's having
three square meals a day.

Intense bursts of energy pulse out
from galaxy GSN 069.

We see X-ray flares and bursts

coming from the centre
of this galaxy,

repeating every nine hours,

and each burst is associated
with a new feeding event.

This supermassive black hole
not only eats on a schedule,

it has a very healthy appetite.

Each one of these meals
that this black hole is consuming

is the equivalent of four
of our moons in a single bite.

So what exactly is this supermassive
black hole consuming?

The most likely contender is a star.

We think that
the star has been ripped apart

and spread throughout
an accretion disk,

and then slowly
over the course of hours,

an instability builds up,
and some material falls in.

When the infalling material
from the star

hit the supermassive black hole,
it triggered a burst of X-rays.

Then, the system stabilised...
until it sparked up again...

..creating a nine-hour cycle
of bursts of energy.

Then, in 2020, new observations
spawned a different theory.

The star wasn't caught
on the accretion disk.

The supermassive black hole
had instead pulled it into orbit.

Its orbit takes it near
that black hole every nine hours,

and every time
it encounters the black hole,

some of its material
gets sipped off.

Eventually, the GSN 069
supermassive black hole

will lose its meal ticket.

But it's luckier than many
other supermassive black holes.

Sometimes black holes
just take a little nibble

on the surrounding material
and just give a little burp

of radiation in response.

A black hole burp
generates strong shockwaves

that radiate out
across the universe.

We detected two of these
energy outbursts

in galaxy J1354+1327,

located 800 million
light-years away.

The huge burps suggested
that the supermassive black hole

at the core of this galaxy
was snacking.

It ate a bunch of material one time

that caused a burst of energy
flowing outward.

Then it feasted again,
and that caused another burp.

What caused
these separate outbursts?

The belching black hole galaxy
has a smaller companion galaxy.

A gas stream links the two galaxies,

supplying an intermittent,
on-off food supply.

There's actually
a smaller satellite galaxy

going around the bigger galaxy,
the black hole in the middle

is pulling streams of material off
this little galaxy.

Clumps of material
from the companion galaxy

move toward the centre of J1354.

Once there, the supermassive
black hole grabs them.

Some gas streaming
from the neighbouring galaxy

reaches the centre
of the bigger galaxy

when the black hole feeds
and then ejects a jet.

When supermassive
black holes like the one

in J1354 receive
an irregular supply of food,

a cycle is established,

a routine that scientists
call feast...

..burp, (SONIC WHOOSH)
nap.

The supermassive black hole
we're headed towards, M87 star,

doesn't do burp and nap.

It feasts all the time.

Stars come in and get ripped apart,

maybe once every
10,000 or 100,000 years.

Whereas M87 has been shining
brightly for millions of years.

It clearly has a supply of gas
other than ripped apart stars

that's feeding the accretion disk.

This helps explain how M87 star
grew to 6.5 billion solar masses.

But what about the future?

Will this supermassive black hole
continue to feast...

..or will it starve?

To find out,
we have to move even closer...

..across the accretion disk,

to discover just how M87 star
satisfies its insatiable appetite.

Our ship passes over
the accretion disk of M87 star,

a blazing ring of gas and dust
hundreds of light-years across.

This is the supermassive
black hole's grocery store.

Black holes are known for sucking
in everything.

But is that really true?

Black holes don't really suck.
It's a popular misconception.

They don't just pull anything in.

In fact, if the sun just instantly
turned into a black hole today,

the Earth would happily continue
on in its orbit,

because all that gravity cares about
is how massive

and how far away something is.

Supermassive black holes
like M87 star

are a lot more massive
than a regular sun-sized black hole.

This means their gravity is greater

and extends much farther
out into the galaxy,

allowing supermassive black holes
to attract dust,

gas clouds, and stars
from billions of miles away.

But they don't gulp down
everything they pull in.

HAKEEM: The way black holes
eat matter

isn't as straightforward
as you might imagine.

Earth gains mass every day

from objects falling to it
from space.

So you might imagine that matter

falling onto a black hole is
like meteorites falling onto Earth.

They can come in from any direction
and land anywhere.

(BOOM)

That's not the case around
a supermassive black hole.

The most efficient way
for a black hole to consume matter

is for it to grow
an accretion disk.

Accretion disks grow
when gas and dust dragged in

by the supermassive
black hole's gravity

spirals inward
and piles up in a ring.

The ring starts to spin
from the combination of gravity,

and the momentum of the gas
and dust.

The spinning material
flattens into a disc.

The material
doesn't fall straight in.

It orbits its way in,

and so it gets accelerated
to incredibly fast speeds.

Sometimes, the matter ends up
inside the black hole.

Sometimes,
the matter ends up getting
kicked away from the black hole.

As we travelled through M87,

we witnessed jets and winds
(SONIC WHOOSHING)

from the supermassive black hole

blast this material
out into the galaxy.

But there may be other things
that stop food

from entering a black hole.

The black hole at the centre
of our Milky Way galaxy,

what we call Sagittarius A star,

appears to be swallowing material
or eating at an incredibly low rate.

To discover what's stopping
Sagittarius A star,

or Sag A star for short,
from feeding,

scientists studied infra-red light

moving out from the supermassive
black hole.

To do that, they needed to fly high
in Earth's atmosphere.

The problem is,
water vapour in our atmosphere

prevents the infra-red light
from space

from getting down to the ground.

SOFIA is an infra-red telescope
built into the side of an airplane.

As bizarre as that is,
it's a very stable platform.

SOFIA can look at these objects
emitting infra-red in space

and get really good observations
of them.

SOFIA focuses
on the structure of the gas

in the strong magnetic fields
at the centre of the Milky Way.

This high-resolution
telescope can track

the finest grains of dust.

When all the dust grains in a cloud
are aligned by a magnetic field,

they scatter the light
coming at them in a certain way,

and we call this polarised light.

The dust grains can actually
map out the magnetic field

embedded in that dust cloud.

The telescope picked out the grains
arranged in a spiral pattern

and revealed the direction
the grains were moving.

This movement reveals
why Sag A star is starving.

The magnetic field
is channelling them

into orbit around the black hole
instead of allowing them to fall in.

So it's literally keeping
those dust grains

away from the black hole.

The magnetic fields
also pushed clouds of gas,

Sag A star's food source,

away from the supermassive
black hole.

This is the situation now,
but that's not necessarily

the way things
are always going to be.

Because magnetic fields
can switch directions.

There's other junk
out there, dust and gas

and other stars,
that as they get close,

they can change the magnetic field,

and that might allow that dust
to fall into the black hole.

Magnetic fields changing direction
offers hope for Sag A star.

And magnetic fields
could help M87 star feed.

Our mission continues,
following this material

plunging down
into the supermassive black hole.

We set a course
towards the event horizon.

The boundary between the known
and the unknown universe,

where the laws of physics,
no longer apply.

Our ship crosses the accretion disk.

Ahead, the absolute darkness

of the supermassive black hole,
M87 star.

According to black hole legend,

this is where we meet our end,
torn to shreds by gravity.

We have so much wonderful
imagery of what would happen

if you fell into a black hole
from science fiction.

One idea that has caught
popular attention

is the notion you get spaghettified
when you fall into a black hole.

This is me.
This is a black hole...

..which is pulling stronger
on my feet than on my head.

And if this black hole
is a little bit heavier

than our sun.

This difference in pull is so strong

that I would actually
get spaghettified, torn apart.

(SWOOSHING)

So will M87 star spaghettify us?

The answer depends
on the black hole's mass

and volume ratio.

A stellar mass black hole
with the mass

of 14 suns is just 26 miles across.

That's about the size
of Oklahoma City.

Such an enormous mass
in a small volume

creates a very sharp increase
in gravitational tidal forces

as you approach the black hole.

With a small black hole,
the strength of gravity

changes so rapidly with distance
that your feet could be pulled

a million times harder
than your head.

But with supermassive black holes,
that doesn't happen.

The mass of a stellar mass
black hole

is concentrated in a small area.

A supermassive black hole's mass
spreads much wider

over an area
a billion times larger...

..so its gravity increases gently
as you get closer.

This means approaching
a supermassive black hole

feels more like walking down a slope
rather than jumping off a cliff,

so it won't rip you to shreds.

Supermassive black holes
have a bad reputation.

That bad reputation firmly
belongs to stellar mass black holes

that rips things to shreds.

The nice thing
about supermassive black holes

is these so-called tidal forces
are much weaker,

so I would actually be just fine
and be able to take in

this really bizarre scenery
around the black hole,

with light from distant objects
being bent out of shape.

So we can approach M87 star safely.

Once there, we are faced
with an awe-inspiring sight.

The supermassive black hole
distorts the light around it.

Far away from the black hole,
that warping isn't very strong,

but the closer the light
gets to the black hole,

the more severely its path
is distorted,

and the starlight
around the black hole

becomes really bizarre.

They get stretched into, into rings
and arcs.

We can even see things hidden
behind the supermassive black hole.

I would see, for example,

the galaxy behind here looking
completely warped out of shape,

because light is bent
around the black hole.

Black holes can even bend light
so it comes from my face,

goes around and comes back
on the other side.

So I could, in principle,
use a black hole,

you know, as a mirror
when shaving.

PAUL: To really understand
what's happening

around a black hole,
we need to understand gravity,

and the language of gravity
is the language of space-time.

Space-time binds
the whole universe together.

If we could put on
special space-time glasses,

we'd see stars, planets,

and galaxies floating
on a grid of space-time.

These objects have mass,

and mass distorts
and curves space-time.

Imagine a trapeze artist
with a flat net underneath them.

When they fall
from the trapeze onto that net,

the net distorts, it forms a dimple
right where that trapeze artist is.

The trapeze artist
is like a black hole.

The net is like the fabric
of space and time

distorting because of
the mass in it.

This distortion
of the space-time net

by objects with mass
is called gravity.

The more massive you are,
the more gravity you have,

because the more you bend
and stretch space-time.

So one trapeze artists
may bend the net a little bit,

but a hundred trapeze artists
will bend that net a lot,

and good luck
trying to walk across it.

M87 star's immense gravity
bends space,

forcing light to travel
along the curves.

But what does it do to the other
half of the equation, time?

Einstein realised
that time actually runs slower

near a black hole
than back on Earth.

It's a process
called gravitational time dilation.

Viewed from a distance,

our ship appears
to move in slow motion.

But what do we see
on board the craft

as we approach M87 star?

You would perceive time
to proceed on normally.

You'd look at your watch,
and one hand

is going around
the dial just like normal.

But to an outside observer,

that apparent one minute
on your watch could take millions

to even billions of years.

If I'm having a Zoom conversation
with mommy back home,

even though I'm feeling
I'm speaking normally,

she would hear me go,
(SLOWLY) "Hi, mommy!"

And this is not
some sort of illusion.

My time really is going slower.
So when I come home,

she'd be like, 'Hey, Max, you look
so good, you look so youthful,'

and I would actually have aged less
because time ran slower over there.

On our final approach into M87 star,

we reach a crucial milestone.

We are now
at the innermost stable orbit.

We go any further,
we're not getting out ever.

You have two choices.

You either escape to safety
or you fall into the black hole.

Well, that's easy.

We detach the probe
to approach the black hole alone.

You can think
of the event horizon as being
the surface of a black hole,

but that's a bit
of a misconception.

There's not actually
anything there.

That's just the distance
from the centre,

where the escape velocity
is the speed of light.

Because nothing can travel
faster than light,

nothing can escape a black hole.

Think of the event horizon
as a waterfall.

If you imagine the flow of water
over a waterfall,

if you're a fish,
you could swim up close
to that edge

and still escape
but if you go too far,

you hit the point of no return,
and you're going over.

At the event horizon,
the water moves faster

than the fish can swim
or our probe can orbit,

so the waterfall, or gravity,
carries them over

and into the black hole.

But what about the light
around them?

Imagine that fish that's going over

the waterfall
is carrying a flashlight.

Say it's an alien fish.

At a black hole, if that fish
goes over that event horizon,

not only does the fish
and the flashlight get sucked in,

but the light of the flashlight
get sucked in.

There's nothing
that can turn around.

Light, matter, cows, elephants
that passes through
the event horizon

can never come back out,
it is a one-way ticket.

A one-way ticket
through the event horizon.

Back on the ship, though,
we don't see the probe

entered the supermassive black hole.

Instead, from our perspective,

the probe just gets slower
and slower and slower and slower.

Until it appears that time
simply stops for the probe,

frozen by the enormous gravity
of M87 star.

The probe appears stuck,
glued to the surface.

But that's just our perspective.

In reality, the probe has already
crossed the event horizon

and is inside the black hole.

If only it was that simple.

The two major theories that explain
how the universe works

don't work at the event horizon.

General relativity says,
the probe enters the black hole...

..but quantum mechanics
throws up some major hurdles.

According to some ideas
rooted in quantum mechanics,

there may be something
called a firewall,

a wall of quantum energies
that prevents material

from actually reaching
through the event horizon.

Our probe is approaching
the event horizon of M87 star,

but there's a problem.

The two major theories that explain
how the universe works

don't agree about what happens next.

One says the probe passes
through unscathed.

The other theory says,
that's impossible.

It suggests the probe
hits an impenetrable barrier

called a firewall.

How can the same event
have two different outcomes?

There's a really interesting puzzle
right now,

which is where general relativity
and quantum mechanics meet,

and it's called
the Black Hole Information Paradox.

What we have is a very
schizophrenic situation in Physics,

where we have two theories
that just don't get along.

Einstein's theory of gravity
explains all the big stuff.

Quantum field theory
explains all the small stuff.

So which one is right
and which one is wrong?

This is the mystery.

General relativity says, in theory,

crossing the event horizon
is no big deal.

If you're passing through
the event horizon,

you wouldn't notice
anything different.

You can, in fact,
cross the event horizon

of a black hole like M87 star
in your spaceship,

without even knowing that you have,
nothing would change,

you'd just peacefully drift inside.

According to general relativity,

our probe crosses the event horizon
and enters the black hole.

Quantum mechanics
sees it differently.

When it looks at the probe,
it doesn't see a robotic spacecraft.

It sees information.

Everything at a quantum mechanical
level has information.

You can think of things
like a particle having a charge.

Particles have spin,
angular momentum,

and that information,
as far as we understand,

can't be destroyed.

What do we mean by "destroyed"?

Well, think of burning a book.

The words are information.

As each page burns,
the words disappear.

The information is gone,
but not really.

If you could track every
single thing that was happening,

track each smoke particle,

put everything back together again,
in principle,

that information is still there.

Because information
can't be destroyed,

the probe's information,
even if mangled,

should be inside
the supermassive black hole.

If the information
that fell into a black hole

just stayed locked inside
of a black hole, that'd be fine.

That doesn't violate any physics.

But Stephen Hawking
threw a wrench in the works

when he theorised that, over time,
black holes evaporate,

slowly shrinking
particle by particle,

emitting heat
known as Hawking radiation.

Hawking radiation itself
doesn't carry any information out,

and Hawking radiation
eventually destroys a black hole.

Eventually, the black hole
evaporates and disappears.

As the black hole vanishes, so too,
does information about the probe.

This is a big problem
for quantum mechanics.

Can black holes really
destroy information even though

quantum physics
suggests you cannot?

So, is the foundation
of quantum mechanics wrong?

This is the Quantum Information
Paradox.

To try to prevent
this impossible situation,

scientists came up
with a workaround...

..something that prevents
the probe's information

from ever entering the black hole,
the firewall.

Quantum mechanics says that
there is this quantum fuzz

causing there to be
ridiculously high temperatures

literally burning you up
as soon as you enter.

If the firewall
incinerates the probe,

then its information will stay
in the ashes of the ship,

just like the words
from the burning book.

So, which theory is right?

Does the probe
safely enter the black hole?

Or does the probe burn up?

I've spent an afternoon
at Caltech arguing

with people, if anything
falls into a black hole or not,

and the answer is,
we don't really know.

To find an answer,
scientists have come up

with some crazy ideas.

One, called quantum entanglement,

suggests that the probe
is both inside

and outside the black hole,

its information carried by particles
constantly popping up

on either side of the event horizon.

And Stephen Hawking,
whose original idea

that black holes lose information
through heat,

also came up with a solution.

He suggested that black holes
have soft hair.

Traditional black hole science says,
they're bald.

By which we mean
that they have no features
at all except their mass,

and their charge and their spin
that you can measure from outside.

Hawking's updated theory
says that black hole hair

is made from ghostly
quantum particles,

which store information.

Thermal radiation
from the evaporating black hole

carries this information away
from the event horizon.

If Hawking is right,
the probe's information

will eventually escape
into the universe.

The concept of black hole hair

would solve the Black Hole
Information Paradox...

...if it exists, but we don't know
if black holes have hair

or if they're, you know, bald.

Until we can unite quantum mechanics

and general relativity
at the event horizon,

the Information Paradox
will remain a problem

for physicists.

It's one of the most
embarrassing problems in Physics,

which is still unsolved.

I hope one of you who watches this

will become a physicist
and solve it for us,

because Physics is far from done.

The failure to solve
the Black Hole Information Paradox

throws up a major obstacle

to our understanding
of how our universe works.

This is the point
where physics hits a wall.

While a search
for a solution continues,

let's assume our probe dodges

its way past
the Information Paradox.

It sails across the event horizon

towards one of the most
violent places in the universe,

the core of M87 star.

It's called the singularity,
and there are no rules.

Nothing makes sense,
and nothing escapes.

Our probe
has crossed the event horizon.

It's on a one-way trip

to the heart of the supermassive
black hole M87 star.

Anything that crosses
the event horizon

is not coming out,
it's like Vegas.

What goes in a black hole
stays in a black hole.

The probe leaves the physics
we understand

and enters the world of Physics
we do not.

This probe is now moving faster
than light

or being carried by space itself
faster than light.

Once you cross the event horizon
of a black hole,

your future lies on the singularity
in the centre of the black hole,

there's no escaping the fact

that you will eventually join
the singularity.

The space inside of a black hole
- is like a 3
- D spinning vortex.

The space in there
is always moving.

This is the nightmare version
of the Carousel ride.

The whirling probe
hurtles downwards,

until it hits an even more bizarre
region of the black hole...

..the inner event horizon.

You thought the firewall was bad,

but that's peanuts compared
to the inner event horizon.

Theoretical physicist
Andrew Hamilton

believes that all light
and matter that's fallen

into a black hole piles up

in a tremendous collision
at this location.

The inner event horizon
would be infinitely violent,

cos it's like the meeting point
between two universes.

This meeting point is like water
falling and smashing into spray,

shooting back up from the rocks
at the base of the falls.

Inside the supermassive black hole,

space races in and crashes
into rebounding space

at the inner event horizon.

This would be a place
of infinite energy.

It's a place where infalling
material, into the black hole,

meets outflowing material.

Everything falling into M87 star
smashes together

in a monumental release of energy.

This energy has got to go somewhere.

It's possible that this inner
event horizon is so energetic

that brand-new universes
could be born in this space.

But the question is,
how do you actually sort of birth

a new baby universe?

The energy created
at the inner event horizon

could compress down
into one tiny speck,

which suddenly ignites...

..sparking baby universes
into life...

..in their very own Big Bangs.

We know that, a long time ago,
our own universe was very small,

very hot, and very dense.

It's possible that
it could have been born

in the inner event horizon
of a spinning black hole.

This is such a tantalising
and very hypothetical idea,

but if it's correct,

it gives us insights into
the origins of our universe itself.

Do we have strong evidence
that black holes

create baby universes?
No.

Do we have strong evidence
that they don't? No.

If the probe survives
the inner event horizon,

it then heads towards the strangest
place in the universe...

..the core of a supermassive
black hole.

The singularity.

As the probe gets closer
and closer to the singularity,

the probe gets further and
further away from known physics.

We don't know
what the probe will encounter

when it reaches the singularity.

We don't know what it will find.

We don't know
what it will experience.

We don't know.

In other words,
there's a lot we don't know.

Like what exactly
is the singularity?

It's a hard question to answer.

Traditional science says
it's an infinitely tiny point,

but that's not the case
with M87 star.

What's interesting is that
if your black hole is spinning,

the singularity is not a point,
but it's, in fact, a ring.

Physics says the singularity
is infinitely dense.

A point of space
and time that is, it's collapsed
as far as it will go,

it basically has infinite density
in zero size.

For many scientists,
that's a big problem.

I do not like singularities.

I feel that they sound
really un-physical.

The word singularity sounds
so intimidating and scientific,

but it's honestly just
our physicists' code word for,

"Err, we have no clue
what we're talking about."

Where else in nature
do we find infinities?

We're talking about a region
that would have infinite density

and infinitely small volume,
basically zero volume.

How could that exist?
I just don't see it.

We just don't know. And frankly,
we will never know for sure.

Perhaps, the probe breaks up
and joins material

consumed by M87 star
over billions of years.

Compressed down, not just to atoms,
but to a sea of energy...

..absorbed into a ring
of zero volume and infinite density.

Or there could be
another possibility.

Maybe the singularity
doesn't destroy the probe at all.

Maybe the probe travels
straight on through

and passes into another universe.

Our voyage to the heart of M87 star
has been a wild ride.

We crossed the event horizon
and fell towards the singularity...

..the core of the supermassive
black hole.

Is this the end of our journey
or just the beginning?

It could be that the singularity

isn't the end point
of the probe's journey.

It could be that
the probe passes through

the singularity
and enters into a new universe.

Our probe has another option,

an escape route out of M87 star.

In our universe,
we have black holes,

objects where,
if you enter, you can't escape.

It's also theoretically possible
for there to be white holes,

objects that you can't enter,
you can only escape from.

A white hole is basically
a black hole running backwards.

Some physicists have theorised
that white holes may link

to the singularities of black holes,

connected by something
called a wormhole.

There have been
interesting papers written

suggesting that you could have
a wormhole where

something that falls
into a black hole here

comes out of a white hole
somewhere else.

It sounds like a great way

for the probe to escape
certain death, theoretically.

A wormhole is the bridge
in space-time
between those two things.

It's easy to create in mathematics.

It very well might not exist
in real life

and will almost certainly live out
on our entire civilisation

and never know about it.

That's because constructing a bridge

between a black hole and
a white hole creates a few issues.

A, we don't know
how to build them, for sure.

B, they might be unstable
and collapse on

themselves,
unless you invent...

have some new, weird sort of matter
that can support them.

HAKEEM: The problem is that
it's hard to maintain
this bridge open.

It's not likely
that they would ever have

any practical use
cos they're just not stable.

But if M87 star does have a stable
wormhole linked to its singularity,

where might our probe end up?

It could be that
this probe's journey

doesn't end at the singularity,

and all the information
that it carries with it

could be deposited in some
distant corner of our own universe.

Or perhaps in a different universe.
(SONIC WHOOSHING)

One idea that sounded
like science fiction

decades ago is actually
now considered potential reality,

and that's the idea
of parallel universes.

If parallel universes exist,
then some surmise

that a black hole
could be a gateway

to a parallel universe.

The concept of parallel universes
comes from inflation theory,

the model we use to explain
the first moments of our universe.

The most mainstream
and accepted theory

for how our Big Bang happened
is inflation.

A process whereby
a tiny bit of space

just keeps doubling, doubling,
doubling, doubling

and giving us this.

And the universe expanded so much

you could have created bubbles
in a way.

It's almost like,
trying to boil water

and you turn your burner
on really high.

You start to create these bubbles
and these bubbles

could be these own island universes

that are foaming up
in this endless multiverse.

If there are parallel universes,

who knows which one our probe
may end up in.

This universe may be
just like our own,

or it might be something
completely different.

We'll never get to find out
unless we follow in after it.

It could all work out just fine,

and that probe
just sails on through

and gets to explore new adventures.

We don't know.
Only the probe knows.

Supermassive black holes
are some of the strangest

and most fascinating objects
in the universe.

Ever since
Einstein's Theory of Relativity

predicted black holes a century ago,

we've been trying to understand
how they work.

The photograph of M87 star
confirmed many theories,

but there is still much to learn
about the birth, life,

and death
of these remarkable objects...

..and even more
to leave us fascinated.

This is the ultimate unknown.
This is the real Wild West.

This is the frontier
of human knowledge.

I care about
supermassive black holes

first and foremost
because they are awesome.

They stimulate my childhood
imagination and fascination.

Supermassive black holes offer us

a truly unique window
into how the laws of Physics work,

especially the laws of gravity
in extreme regimes far beyond

anything that we can
possibly imagine here on Earth.

Supermassive black holes lurk at the heart

of almost every large galaxy
that we know of.

So in some way, we're just sort
of all along for the ride

with the supermassive black holes.

If I could make a request
for one special favour

I would get before I die...

..what I would like to do
is to get to just spend a few hours

orbiting the monster black hole
in the middle of the galaxy.
What a way to go, heh.

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