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 by vitac... www.vitac.com
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,
that distance shrinks its apparent size
to just a tiny little dot on the sky.
To see the tiny dot,
we need a telescope the size of the Earth.
How do you possibly do that?
You can't build that telescope, right?
Well, there's a trick.
You actually get a few different telescopes
and you spread them out over the surface of the Earth.
And when we had all of these sites together,
we wind up being able to take an image of something
that is really, really impossibly small.
To gather enough light to see a target this small,
the team take long-exposure images
of Sagittarius A-star's shadow...
...but there's a problem.
The accretion disk moves too much for us
to capture a clear image.
When you're taking a long exposure of a person,
right, you need them to be really,
really still, right?
Because if they're moving around a lot,
they're going to blur the image out.
And that kind of thing is happening
when we observe Sagittarius A-star
because it is unwilling to sit still for us.
It is booming and banging and flashing
on the timescale of literally hours.
As glowing material orbits the black hole
at 30% the speed of light,
Sagittarius A-star's shadow blurs.
Future developments may allow us
to see Sagittarius A-star clearly.
For now, we can't capture an accurate image
of our galaxy's supermassive black hole.
But the hunt to see a supermassive black hole
wasn't over.
The Event Horizon Telescope turned to another galaxy
54 million light-years away... M87.
M87 is an absolute beast of a galaxy.
It's the so-called brightest cluster galaxy.
These are among the largest galaxies in the universe.
And M87 is home
to another supermassive black hole...
the giant M87 star.
M87 star is so massive that the gravitational region
that's interesting is actually easier to image
than the black hole in our own galaxy.
M87 star is over a thousand times more massive
than Sagittarius A-star
and has a far larger accretion disk.
When photographing a black hole, size matters,
because big accretion disks project more stable light,
so images of them don't blur as much.
In April of 2019,
the event horizon team unveiled their image.
We have seen what we thought was unseeable.
We have seen and taken a picture of a black hole.
I've been working on this project
for almost six years now, and so, this is something
we've been looking forward to for a really long time.
Capturing this image took decades of work
by hundreds of scientists all over the world.
I was really stunned.
Suddenly, when you say that's the real thing, that's amazing.
It really affected me.
This is something 6 1/2 billion times
the mass of the Sun,
55 million light-years away and we're looking at it.
So when you look at the image, it's totally fine.
You're totally forgiven for thinking,
"ah, it looks a little blurry."
But I cannot reiterate enough
how profound this image actually is.
We are seeing just a hair's width away from a discontinuity
in the fabric of space-time itself.
Actually seeing so close to an actual event horizon,
a discontinuity in the fabric of space-time,
never seemed possible.
This image of the heart of a distant galaxy
helps us understand supermassive black holes like never before.
When we observe supermassive black holes
in other galaxies, including the one in m87,
we're able to learn more about the big picture
of how these massive black holes form and evolve over time.
And that in turn, helps us understand
how our Milky Way galaxy
and its super massive black hole has formed.
By studying, not just making images of black holes,
but making videos of black holes,
and seeing as that gas is spinning around it,
we can try to map around a black hole more precisely
and learn about its dynamics.
An image of Sagittarius A-star
remains out of reach,
but in 2018, it shows a deadly side to its character.
The supermassive black hole's accretion disk
releases huge, powerful flares,
and they could be pointed right at us.
In 2018, astronomers were studying a special star
orbiting our galaxy's supermassive black hole.
The star passes close to Sagittarius A-star...
every 16 years.
It's called S2, and by studying this star's fly-by,
we hope to learn more about Sagittarius A-star.
We think that S2 may be the very closest star
to the supermassive black hole in the center of our galaxy.
At closest approach to sag A-star,
S2 comes within 17 light hours or so of the surface.
The supermassive black hole's powerful gravity
accelerates the star to 17 million miles an hour.
That's fast enough to travel from New York to L.A.
In half a second,
but it's not the star's speed that excites scientists.
This is a great star, because it's on an elliptical orbit
that takes it fairly far from the black hole,
but every few years,
it passes right above the supermassive black hole.
As we tracked S2's swing around Sagittarius A-star,
we detected powerful bursts of infrared light
coming from the direction of the supermassive black hole.
There's a blob of gas
that is orbiting very close to the black hole,
and it was flaring as it went around.
There were three separate flares of light
that they were able to detect.
The flares didn't come directly
from the supermassive black hole,
they came from the material around it.
The flares that were discovered are thought to originate
from magnetic storms
in this very, very hot turbulent gas around the black hole.
The extreme heat in the accretion disk
strips electrons from atoms of gas.
The stripped electrons and hot gas form a plasma,
which creates powerful magnetic fields
when accelerated to high speeds.
Because some super massive black holes
have these superheated,
rapidly spinning vortices of gas swirling around them,
you get these very, very powerful,
very tightly wound magnetic fields.
And there's energy stored in that magnetic field.
It's like a bunch of piano wires all tangled up.
And if these things interact with each other, they can snap,
and when they snap, that energy is released.
You'll get this enormous release of energy
as these coils of magnetic fields effectively snap.
And when they do so, just like on the surface of our sun,
they release an enormous flare of gas.
These powerful flares can be millions of miles wide
and come packed with superheated gas and plasma.
Solar flares release as much energy
as 10 million volcanic explosions.
Flares from Sagittarius A-star's accretion disk
are like millions of solar flares all going off at once.
It's kind of like comparing a nuclear weapon to a firecracker.
Sagittarius A-star's flares
release intense blasts of radiation,
but by watching the flares from Earth,
we can learn about the orientation
of the supermassive black hole's accretion disk.
This gas that's in this accretion disk
around the black hole is like a friendly helper
shining a flashlight back toward Earth.
And we can watch the orbit of these flashlights
and help understand the orientation of gas
that swirls around the black hole.
We think we're getting a bird's-eye view of it.
And looking down the barrel,
we're looking at the accretion disk basically face-on.
That means that any material that gets blasted away
from the black hole could be aimed right at us.
Should we be worried about the flares reaching Earth?
It sounds worrisome, this blob of gas
emitting these huge flares of light,
but you've got to realize, this is 26,000 light-years away.
That is a long way.
It took an extremely sensitive detector
on one of the largest telescopes on Earth
to be able to see this at all.
Earth is safe for now,
but the more we learn about the galaxy center,
the more terrifying it becomes.
We know of Sagittarius A-star,
the central supermassive black hole,
but now we're beginning to suspect
that it might not be alone.
A dangerous swarm of black holes
could be racing around the center of the Milky Way.
Thousands more may be hiding from sight.
The supermassive black hole, Sagittarius A-star,
dominates the center of the Milky Way...
...affecting star formation...
...and carving out vast gas bubbles in space.
But Sagittarius A-star might not be the only black hole in town,
or even the most dangerous.
We've known for a long time
that there's a supermassive black hole
in the very heart of our galaxy,
but there may be an angry swarm of smaller black holes,
buzzing all around it.
In April of 2018,
astronomers led by Columbia university
revealed the results of a hunting mission
in the center of the galaxy.
They'd used 12 years of Chandra observatory data
to seek out stellar mass black holes.
Black holes that are made from the death of stars,
from supernova explosions,
are called stellar mass black holes.
And these are made from stars
that were many times the mass of the sun.
Finding stellar mass black holes is tough.
Light can't escape a black hole's gravity,
so we can't see them directly.
And stellar mass black holes are only tens of miles wide,
making them almost impossible to detect.
So astronomers look for a special type
of stellar mass black hole.
One of the ways that we look for stellar mass black holes,
is that they often are vampires eating a companion star.
These vampires are part of a binary pair,
a stellar mass black hole in orbit with a living star,
the black hole feasting on its partner.
That black hole
is like a very, very deadly parasite for that star.
It is ripping mass off the surface of that star,
and that matter is raining down toward the black hole itself.
And that material lights up,
so this allows us to hunt for black holes,
not through taking pictures of black holes directly,
but through seeing the material falling to its doom.
The problem is,
gas and dust spread throughout the galaxy
stops visible light from the binary pair reaching Earth.
But the binary pair release another type of light
that passes through the gas and dust more easily...
X-rays.
The system itself is emitting X-rays,
so they're called X-ray binaries.
So these are useful, because the X-ray emission
can be very powerful
and can be potentially seen from the Earth,
even though the binary is very far away,
say, at the galactic center.
The glowing disks of material in X-ray binary systems
are almost a million times smaller than the accretion disk
surrounding Sagittarius A-star, too small
for us to see the material swirling around them in detail.
So, we see the X-ray binaries as pinpricks of X-ray light.
Astronomers detect 12 of these X-ray binaries
in a small 3-light-year-wide patch of space
at the galactic center.
And that means that there could be a much larger collection
of these relatively tiny stellar mass black holes
in the heart of our galaxy.
If black holes form the way we think they do,
there very likely may be swarms of black holes
racing around Sagittarius A-star.
But X-ray binaries that are powerful enough for us
to detect are incredibly rare.
So we estimate that for the dozen X-ray binaries discovered,
there could be up to a thousand more.
In total, there could be 20,000 stellar mass black holes
in this 3-light-year region of space.
Why are these black holes swarming in the galaxy center?
It appears they've migrated from the rest of the Milky Way.
Through a process called dynamical friction,
black holes can actually sink to the centers of galaxies
very, very rapidly, like dropping a stone into a pond.
What that means is that an errant,
wandering black hole might eventually
find its way toward the center of our own galaxy,
where Sagittarius A-star resides.
As stellar mass black holes orbit the galaxy,
they interact gravitationally
with stars and clouds of gas and dust.
These interactions push the black holes
towards the center of the galaxy,
where the black holes swarm.
A swarm of stellar mass black holes sounds deadly,
but it may not be the most lethal thing
in the center of the Milky Way.
A surprising observation indicates that there is a lot
of antimatter in the center of our galaxy.
And when antimatter meets matter,
the results are explosive.
In 2017,
astronomers tried to solve a decades-old cosmic mystery...
...unexplained high-energy radiation
streaming through our galaxy.
At first, we didn't know where it was from.
But we discovered it was gamma radiation
coming from somewhere in the center of the Milky Way.
The question is, what's making these gamma rays?
That's hard to do.
It's not like you can rub your hands together
and generate gamma rays.
When we took a closer look at the gamma rays,
we discovered the signature of the most explosive substance
in the universe... antimatter.
Antimatter is like normal matter
but with opposite charge.
That's it. It's matter's evil twin.
When evil twin meets good twin,
it is not a happy reunion.
Antimatter is scary.
It's not like you want to have some in your kitchen.
This stuff is very, very explosive,
if you want to think of it that way.
If it touches normal matter,
it releases a huge amount of energy.
When matter and antimatter combine,
they annihilate each other and transform
into high-energy radiation, just like the gamma rays
seen streaming out of the center of the Milky Way.
We see antimatter throughout the galaxy,
but strangely, the galactic center
seemed to have 40% more antimatter than anywhere else.
Right now in the heart of our galaxy,
we actually observe fountains of antimatter
that are producing 10 trillion tons
of antimatter every second.
One of the big questions that we've wondered about
for a very long time, is what's the origin of this stuff?
Initially, there were several suspects.
One possible source of antimatter
is the central black hole, Sagittarius A-star.
Matter can be swirling around this
and it can have such high energy
that it can create antimatter.
But the antimatter
isn't coming from a single point,
it's spread across thousands of light-years of space.
So Sagittarius A-star
can't be the source of the gamma-ray stream.
Another suspect was dark matter.
One of the biggest mysteries in the universe
right now is dark matter.
We know that the majority of mass in the universe
is not in the same form that we are.
It's not made of atoms,
but whatever sort of particle it is or may be,
if these things collide, they can produce antimatter,
and that will produce the gamma rays.
So it's possible that as we look into the heart of the galaxy
and see these extra gamma rays,
that's the signal that dark matter is there.
But the gamma ray stream we detected is too weak
to have been created by dark matter.
Then we had a breakthrough.
We discovered that a special metal called titanium-44
could be responsible for the gamma-ray stream.
Titanium-44 is a highly radioactive element.
That means that it wants to decay
into other types of nuclei.
When titanium-44 decays,
it gives off antimatter.
But to produce the antimatter seen in the galaxy's core,
you would need a lot of titanium-44.
It could be created in rare energetic events,
in the collision of two dead stars... white dwarfs.
A white dwarf star is a star that didn't have enough mass
when it died to actually become a supernova.
It just sort of cools off as a dead little cinder.
But what if you have two white dwarfs
that are orbiting around each other,
and as they come closer and closer and collide,
all of a sudden now, you have enough mass
to actually kick a supernova explosion off.
These particular kinds of supernovae
are very good at producing titanium-44.
So these kinds of supernovas are very, very good
at making antimatter.
These supernovas erupt in the core of the galaxy
once every 2,000 years.
But outside of the core in the disk of the galaxy
where our solar system orbits...
...these supernovas happen three times as often.
So the gamma ray observations were wrong.
There isn't more antimatter in the heart of the galaxy.
It's our region of the galaxy
that contains the most antimatter.
Question is, are we in danger?
If you take an ounce of matter
and an ounce of antimatter and collide them,
you're generating a megaton of energy,
the equivalent of a million tons of TNT exploding.
So you don't need much antimatter to generate
a vast amount of energy.
But the thing you have to remember is we live
in this wonderful, dramatic environment
of a larger universe.
It's not dangerous.
It's very far away from us, and it's fascinating.
But all of this antimatter is being produced in our galaxy,
so just sit back and enjoy the fireworks.
The center of the Milky Way
is violent and extreme,
but things could get a whole lot worse.
Rogue supermassive black holes
could be lurking near our galaxy,
and they have the power to end life as we know it.
The Milky Way is around 100,000 light-years across,
and it's home to at least 200 billion stars,
but it hasn't always been this large.
We know that our Milky Way galaxy grew to the size
it is now, which is huge, by eating other galaxies.
And some of these galaxies would've had
supermassive black holes in their centers.
When the Milky Way's gravity
pulled in smaller galaxies,
most of their material merged with the Milky Way,
but some material like stars,
could've been slung tens of thousands of light-years
out of the Milky Way.
This could've happened to a smaller galaxy's
super massive black hole.
It is entirely possible
there are supermassive black holes
wandering around out there, not in the center.
So how could it be possible that there's actually
a supermassive black hole close to us wandering around,
but we never even see it?
Well, remember black hole means it's really, really black.
It actually absorbs radiation and any energy.
So unless something is falling into a black hole
or orbiting around it, you're not going to see it.
And so, if this supermassive black hole
were hypothetically wandering the outskirts of our galaxy,
well, there's a lot less gas there
for that black hole to run into.
And if there's no gas around
that black hole, we will not see it.
The rogue supermassive black hole may not stay
in the outskirts of the galaxy forever.
Gravitational interactions slowly pull it back
into the Milky Way.
Billions of years later,
the supermassive black hole could arrive in the center.
When this rogue supermassive black hole meets up with
Sagittarius A-star, the fuse is lit.
The pair spiral towards each other...
...spinning faster and faster,
reaching up to half the speed of light.
Finally, the two black holes merge.
You would have
an enormously energetic event on your hands.
Those supermassive black holes could, in principle,
merge together, create a huge blast of gravitational waves,
accompanied by a profoundly energetic flash of light
that could, in principle, endanger all life on Earth.
It's literally a stretching
and contracting of space itself.
It's like grabbing the framework of space
and it's shaking it really hard.
And if this happens in our galaxy,
the amount of energy emitted, that would be bad.
When the black holes collide,
they release more energy
than all the stars in the galaxy combined.
Should we be panicked about this?
And the answer is no.
The Earth has been orbiting the sun
for 4 1/2 billion years without any incident, right?
We're pretty safe from them.
If we were around to see the two black holes collide,
we'd witness the most destructive light show
in the history of the galaxy.
But for now, the center of our galaxy is relatively quiet,
but it's still a terrible place to be.
The center of our Milky Way is not a friendly place.
It's nowhere you want to be. It's a bad neighborhood.
You've got tons of stars, tons of radiation,
and stars are being born and dying and exploding.
You've got the central supermassive black hole.
You've got a potential swarm of black holes.
You've got accretion disks. You've got flares.
You've got magnetic outbursts. You've got jets.
Let's just stay out here in the suburbs, all right?
The center of our galaxy
is one of the most nightmarish places in the cosmos.
It's also home to some of the most incredible forces
the universe has to offer.
Whatever the future holds for our galaxy...
...the core of the Milky Way will be at the center of it all.
Our home galaxy, the Milky Way, is our safe harbor,
our island in this vast, cosmic ocean.
And so to understand the heart of our galaxy,
is to understand our home in this cosmic void.