How the Universe Works

26,000 light-years from Earth,

shrouded in cosmic dust and gas

is a mysterious region of space...

the center of the Milky Way.

The center of the Milky Way galaxy is one of the strangest,

most exotic and violent places in our galaxy.

Gas streaming everywhere,

radiation blasting out,

stars moving willy-nilly.

And at the very heart is the mysterious black hole,

4 million times the mass of the sun.

Now we're exploring the center of the Milky Way

like never before,

uncovering powerful forces that affect us all.

Everything that happens at the center of the Milky Way galaxy

really is connected to what's going on

in the rest of the Milky Way.

Understanding the center of our galaxy

unlock secrets of our past, present and future.

captions paid for by discovery communications

March 2019.

We focus the XMM-Newton space telescope

on a region of space around Sagittarius A-star,

the supermassive black hole at the heart of our galaxy.

We spot two huge columns of gas glowing in X-ray light.

The columns seem to be coming from Sagittarius A-star.

We see giant fountains of gas

extending outward from the central region

as though it's like a wind or a giant expulsion event.

The fountains of gas extend 500 light-years above

and below the supermassive black hole.

That's over a million times the distance

from the sun to Neptune.

It looks like this material

is actually leaving the vicinity of the black hole,

like it's burping out these giant, hot X-ray chimneys.

So why is Sagittarius A-star burping out hot gas?

Typically, around a black hole, you have an accretion disk

funneling material into the black hole,

but all of it doesn't end up in the black hole.

There is a little bit of gas

falling onto it right now, even as I'm speaking, right?

As gas falls toward the supermassive black hole,

it becomes super heated.

It liberates an enormous amount of energy

and that energy has to go somewhere.

As gas spirals towards the black hole,

some of the material accelerates to near the speed of light.

It blasts out from the accretion disk...

...creating chimneys of superheated gas

that seem to connect

to two of the largest structures in the galaxy...

the Milky Way's Fermi bubbles.

A few years ago, we noticed that, in fact,

there are these giant bubbles coming out of the very heart

of the Milky Way galaxy.

In each direction,

there's a bubble 25,000 light-years long.

But the gas-filled bubbles

dwarf the chimneys of superheated gas.

Scientists wonder if another more powerful force

blew the bubbles.

So what could have created all of this superheated gas

that actually blew these tremendously large bubbles?

Supermassive black holes in other galaxies

might offer clues.

Black holes at the centers of galaxies

go through different phases.

So they can be either active or they can be calm.

Sometimes black holes at the centers of galaxies

go through an active phase.

And when that happens,

the black hole is actively feeding on material around it,

which means it's growing

and it also gives off huge jets of radiation.

Calm supermassive black holes

release a trickle of hot gas.

But when lots of material falls on them,

they can shoot out jets up to millions of light-years long.

At the current time,

Sagittarius A-star is what we call quiescent.

It's quiet.

There is some material swirling around it,

but really not very much.

But we don't think that's always been the case.

The centers of galaxies are busy places.

There are stars there. There's gas there.

There's dust there,

and sometimes these things fall into that black hole.

6 million years ago,

Sagittarius A-star may have had a feeding frenzy...

...eating too much

and blasting out the remains in huge jets.

Those jets plow through the galaxy

initially at near the speed of light.

And as they do so, they can wreak havoc

or sculpt the evolution of the galaxy

that they're propagating through.

Sagittarius A-star's jets

blasted gas out of the galaxy,

creating the scars we see as the Fermi bubbles.

Now, whatever caused those jets seems to have turned off.

It's not happening anymore

and we're seeing sort of the leftovers of them.

But this is clearly a sign

that sometime in the past few million years,

the black hole in the center of our galaxy,

Sagittarius A-star, was actively feeding on material around it.

Material was falling into it and blasting out this stuff.

The jets left destruction in their wake.

They may have also affected the growth of our entire galaxy.

These structures at the center of our galaxy are important

because they can either shut off star formation

or they can trigger star formation.

As those jets propagate through the galaxy,

they pile up gas

and that gas can be then triggered into star formation.

But these jets can also impart so much heat or energy feedback

into the environment that they prevent star formation.

So black holes in many ways conduct an orchestra,

instructing or dictating when stars can and cannot form.

In the center of the Milky Way,

star-formation rates seem low.

The jets could be responsible.

But in 2017, the Alma telescope discovered

that change is coming.

So Alma's actually been able to peer in

to the heart of our galaxy

and see that near all this destruction,

there might actually be a new generation of stars forming.

Today, our calm supermassive black hole

could be helping star formation in the core.

But the Fermi bubbles could be evidence of a time

when Sagittarius A-star shut down star formation.

Could the supermassive black hole

roar back to life in the future?

Sagittarius A-star could roar back to life

by just dumping some gas onto it.

And there's a lot of gas at the center of our galaxy

and it could wander into the proximity

of Sagittarius A-star

and ultimately fall onto the event horizon

and that would light it up.

If Sagittarius A-star eats enough gas...

...it could shut down star formation in the galaxy

for millions of years.

It could also give off X-rays and gamma rays

that may hit the Earth.

Thankfully, our central supermassive black hole

is pretty quiet and massive feeding events,

massive energy events are very, very rare.

We don't necessarily have much to worry about.

Sagittarius A-star has reshaped our galaxy.

If we want to survive in the universe,

we need to know more about this monster black hole.

The Event Horizon Telescope is on a mission to do just that.

Question is can it succeed?

The center of the Milky Way

is home to a supermassive black hole,

Sagittarius A-star.

At least we think it is.

We've never seen the supermassive

black hole directly.

But we have seen stars racing around the core.

The speeds of the stars

zipping around the center of our Milky Way galaxy

indicate that there's something very massive

and very compact there,

indeed, 4 million times as massive as our Sun

in a volume smaller than that of our solar system.

It's got to be a black hole basically.

By measuring the orbits of stars

in our galaxy center...

...we estimate that Sagittarius A-star

is over a hundred times wider than our sun.

But despite its size, the black hole is hidden.

One of the immediate challenges

of actually observing black holes

is the fact that they don't emit light and so you can't see them.

Right? So we've never actually seen a black hole.

We've only seen the stuff around a black hole

or we have seen the effects that that black hole

imparts on its ambient surroundings.

That's where the Event Horizon Telescope came in.

Its goal was to photograph Sagittarius A-star,

not the black hole itself, but its shadow.

Around it is this a gas that is moving around the black hole

that's super heated to millions of degrees.

And what the Event Horizon Telescope

is trying to see is the shadow of a black hole.

Light from the hot gas around Sagittarius A-star

frames the giant shadow.

It could be up to 93 million miles across.

Problem is Sagittarius A-star is so far away

that the supermassive black hole is still incredibly hard to see.

Sagittarius A-star is big,

but it's 26,000 light-years away.

A single light-year is 6 trillion miles.

So this is a long, long walk.

And even though it's big,