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26,000 light-years from Earth,
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shrouded in cosmic dust and gas
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is a mysterious region
of space...
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the center of the Milky Way.
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The center of the Milky Way
galaxy is one of the strangest,
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most exotic and violent places
in our galaxy.
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Gas streaming everywhere,
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radiation blasting out,
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stars moving willy-nilly.
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And at the very heart
is the mysterious black hole,
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4 million times
the mass of the sun.
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Now we're exploring
the center of the Milky Way
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like never before,
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uncovering powerful forces
that affect us all.
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Everything that happens at the
center of the Milky Way galaxy
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really is connected
to what's going on
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in the rest of the Milky Way.
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Understanding
the center of our galaxy
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unlock secrets of our past,
present and future.
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Captions by vitac...
www.vitac.com
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captions paid for by
discovery communications
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March 2019.
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We focus the XMM-Newton
space telescope
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on a region of space
around Sagittarius A-star,
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the supermassive black hole
at the heart of our galaxy.
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We spot two huge columns of gas
glowing in X-ray light.
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The columns seem to be coming
from Sagittarius A-star.
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We see giant fountains of gas
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extending outward
from the central region
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as though it's like a wind
or a giant expulsion event.
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The fountains of gas
extend 500 light-years above
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and below the supermassive
black hole.
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That's over a million times
the distance
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from the sun to Neptune.
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It looks like this material
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is actually leaving
the vicinity of the black hole,
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like it's burping out
these giant, hot X-ray chimneys.
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So why is Sagittarius
A-star burping out hot gas?
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Typically, around a black hole,
you have an accretion disk
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funneling material
into the black hole,
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but all of it doesn't end up
in the black hole.
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There is a little bit of gas
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falling onto it right now,
even as I'm speaking, right?
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As gas falls toward
the supermassive black hole,
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it becomes super heated.
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It liberates an enormous amount
of energy
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and that energy
has to go somewhere.
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As gas spirals towards
the black hole,
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some of the material accelerates
to near the speed of light.
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It blasts out from
the accretion disk...
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...creating chimneys
of superheated gas
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that seem to connect
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to two of the largest
structures in the galaxy...
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the Milky Way's Fermi bubbles.
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A few years ago,
we noticed that, in fact,
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there are these giant bubbles
coming out of the very heart
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of the Milky Way galaxy.
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In each direction,
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there's a bubble
25,000 light-years long.
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But the gas-filled bubbles
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dwarf the chimneys
of superheated gas.
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Scientists wonder
if another more powerful force
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blew the bubbles.
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So what could have created
all of this superheated gas
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that actually blew these
tremendously large bubbles?
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Supermassive black
holes in other galaxies
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might offer clues.
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Black holes at
the centers of galaxies
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go through different phases.
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So they can be either active
or they can be calm.
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Sometimes black holes
at the centers of galaxies
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go through an active phase.
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And when that happens,
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the black hole is actively
feeding on material around it,
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which means it's growing
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and it also gives off
huge jets of radiation.
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Calm supermassive black holes
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release a trickle of hot gas.
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But when lots of material
falls on them,
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they can shoot out jets up
to millions of light-years long.
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At the current time,
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Sagittarius A-star is
what we call quiescent.
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It's quiet.
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There is some material
swirling around it,
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but really not very much.
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But we don't think
that's always been the case.
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The centers of galaxies
are busy places.
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There are stars there.
There's gas there.
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There's dust there,
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and sometimes these things
fall into that black hole.
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6 million years ago,
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Sagittarius A-star
may have had a feeding frenzy...
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...eating too much
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and blasting out
the remains in huge jets.
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Those jets plow
through the galaxy
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initially at near the speed
of light.
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And as they do so,
they can wreak havoc
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or sculpt the evolution
of the galaxy
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that
they're propagating through.
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Sagittarius A-star's jets
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blasted gas out of the galaxy,
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creating the scars we see
as the Fermi bubbles.
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Now, whatever caused those jets
seems to have turned off.
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It's not happening anymore
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and we're seeing sort
of the leftovers of them.
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But this is clearly a sign
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that sometime in the past
few million years,
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the black hole
in the center of our galaxy,
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Sagittarius A-star, was actively
feeding on material around it.
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Material was falling into it
and blasting out this stuff.
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The jets left
destruction in their wake.
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They may have also affected
the growth of our entire galaxy.
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These structures at the center
of our galaxy are important
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because they can either
shut off star formation
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or they can trigger
star formation.
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As those jets
propagate through the galaxy,
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they pile up gas
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and that gas can be then
triggered into star formation.
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But these jets can also impart
so much heat or energy feedback
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into the environment that
they prevent star formation.
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So black holes in many ways
conduct an orchestra,
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instructing or dictating
when stars can and cannot form.
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In the center of the Milky Way,
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star-formation rates seem low.
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The jets could be responsible.
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But in 2017,
the Alma telescope discovered
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that change is coming.
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So Alma's actually been
able to peer in
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to the heart of our galaxy
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and see that near
all this destruction,
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there might actually be a new
generation of stars forming.
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Today, our calm
supermassive black hole
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could be helping
star formation in the core.
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But the Fermi bubbles could be
evidence of a time
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when Sagittarius A-star
shut down star formation.
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Could the supermassive
black hole
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roar back to life in the future?
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Sagittarius A-star
could roar back to life
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by just dumping some gas
onto it.
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And there's a lot of gas
at the center of our galaxy
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and it could wander into
the proximity
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of Sagittarius A-star
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and ultimately fall
onto the event horizon
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and that would light it up.
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If Sagittarius A-star
eats enough gas...
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...it could shut down
star formation in the galaxy
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for millions of years.
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It could also give off X-rays
and gamma rays
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that may hit the Earth.
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Thankfully, our central
supermassive black hole
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is pretty quiet
and massive feeding events,
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massive energy events
are very, very rare.
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We don't necessarily
have much to worry about.
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Sagittarius A-star
has reshaped our galaxy.
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If we want to survive
in the universe,
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we need to know more about
this monster black hole.
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The Event Horizon Telescope
is on a mission to do just that.
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Question is can it succeed?
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The center of the Milky Way
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is home to a supermassive
black hole,
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Sagittarius A-star.
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At least we think it is.
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We've never seen
the supermassive
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black hole directly.
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But we have seen stars
racing around the core.
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The speeds of the stars
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zipping around the center
of our Milky Way galaxy
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indicate that there's
something very massive
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and very compact there,
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indeed, 4 million times
as massive as our Sun
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in a volume smaller
than that of our solar system.
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It's got to be
a black hole basically.
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By measuring the orbits of stars
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in our galaxy center...
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...we estimate
that Sagittarius A-star
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is over a hundred times
wider than our sun.
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But despite its size,
the black hole is hidden.
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One of the immediate challenges
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of actually observing
black holes
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is the fact that they don't emit
light and so you can't see them.
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Right? So we've never
actually seen a black hole.
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We've only seen the stuff
around a black hole
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or we have seen the effects
that that black hole
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imparts on its ambient
surroundings.
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That's where the Event
Horizon Telescope came in.
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Its goal was to photograph
Sagittarius A-star,
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not the black hole itself,
but its shadow.
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Around it is this a gas that is
moving around the black hole
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that's super heated
to millions of degrees.
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And what the Event
Horizon Telescope
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is trying to see is
the shadow of a black hole.
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Light from the hot gas
around Sagittarius A-star
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frames the giant shadow.
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It could be up to
93 million miles across.
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Problem is Sagittarius
A-star is so far away
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that the supermassive black hole
is still incredibly hard to see.
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Sagittarius A-star is big,
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but it's
26,000 light-years away.
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A single light-year
is 6 trillion miles.
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So this is a long, long walk.
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And even though it's big,
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that distance shrinks
its apparent size
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to just
a tiny little dot on the sky.
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To see the tiny dot,
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we need a telescope
the size of the Earth.
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How do you possibly do that?
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You can't build
that telescope, right?
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Well, there's a trick.
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You actually get
a few different telescopes
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and you spread them out
over the surface of the Earth.
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And when we had
all of these sites together,
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we wind up being able
to take an image of something
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00:13:14,640 --> 00:13:18,926
that is really,
really impossibly small.
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00:13:18,950 --> 00:13:22,296
To gather enough light
to see a target this small,
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00:13:22,320 --> 00:13:25,096
the team take
long-exposure images
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00:13:25,120 --> 00:13:27,920
of Sagittarius A-star's
shadow...
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...but there's a problem.
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The accretion disk moves
too much for us
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to capture a clear image.
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00:13:42,610 --> 00:13:44,686
When you're taking
a long exposure of a person,
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00:13:44,710 --> 00:13:46,156
right,
you need them to be really,
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00:13:46,180 --> 00:13:47,916
really still, right?
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Because if they're moving around
a lot,
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00:13:49,510 --> 00:13:51,356
they're going to blur
the image out.
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And that kind of thing
is happening
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00:13:52,850 --> 00:13:54,826
when we observe
Sagittarius A-star
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00:13:54,850 --> 00:13:57,226
because it is unwilling
to sit still for us.
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It is booming and banging
and flashing
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on the timescale
of literally hours.
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As glowing material
orbits the black hole
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00:14:06,330 --> 00:14:07,906
at 30% the speed of light,
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00:14:07,930 --> 00:14:11,430
Sagittarius A-star's
shadow blurs.
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00:14:13,840 --> 00:14:16,116
Future developments may allow us
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to see Sagittarius A-star
clearly.
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00:14:21,580 --> 00:14:24,426
For now, we can't capture
an accurate image
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00:14:24,450 --> 00:14:27,280
of our galaxy's
supermassive black hole.
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But the hunt to see
a supermassive black hole
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00:14:33,420 --> 00:14:34,836
wasn't over.
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00:14:34,860 --> 00:14:38,666
The Event Horizon Telescope
turned to another galaxy
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00:14:38,690 --> 00:14:43,560
54 million
light-years away... M87.
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00:14:45,000 --> 00:14:48,076
M87 is an absolute beast
of a galaxy.
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It's the so-called
brightest cluster galaxy.
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00:14:50,240 --> 00:14:53,010
These are among the largest
galaxies in the universe.
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00:14:55,040 --> 00:14:56,886
And M87 is home
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00:14:56,910 --> 00:14:59,756
to another supermassive
black hole...
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00:14:59,780 --> 00:15:02,820
the giant M87 star.
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00:15:04,250 --> 00:15:09,606
M87 star is so massive
that the gravitational region
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00:15:09,630 --> 00:15:12,166
that's interesting
is actually easier to image
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00:15:12,190 --> 00:15:14,600
than the black hole
in our own galaxy.
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00:15:17,670 --> 00:15:22,116
M87 star is over
a thousand times more massive
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00:15:22,140 --> 00:15:24,186
than Sagittarius A-star
252
00:15:24,210 --> 00:15:28,156
and has a far
larger accretion disk.
253
00:15:28,180 --> 00:15:31,486
When photographing a black hole,
size matters,
254
00:15:31,510 --> 00:15:36,026
because big accretion disks
project more stable light,
255
00:15:36,050 --> 00:15:39,250
so images of them
don't blur as much.
256
00:15:42,260 --> 00:15:44,566
In April of 2019,
257
00:15:44,590 --> 00:15:49,106
the event horizon team
unveiled their image.
258
00:15:49,130 --> 00:15:52,716
We have seen what we thought
was unseeable.
259
00:15:52,740 --> 00:15:57,400
We have seen and taken a picture
of a black hole.
260
00:16:05,250 --> 00:16:06,626
I've been working
on this project
261
00:16:06,650 --> 00:16:09,626
for almost six years now,
and so, this is something
262
00:16:09,650 --> 00:16:13,966
we've been looking forward to
for a really long time.
263
00:16:13,990 --> 00:16:16,606
Capturing this image
took decades of work
264
00:16:16,630 --> 00:16:20,490
by hundreds of scientists
all over the world.
265
00:16:23,370 --> 00:16:25,776
I was really stunned.
266
00:16:25,800 --> 00:16:29,716
Suddenly, when you say that's
the real thing, that's amazing.
267
00:16:29,740 --> 00:16:31,486
It really affected me.
268
00:16:31,510 --> 00:16:34,516
This is something
6 1/2 billion times
269
00:16:34,540 --> 00:16:36,186
the mass of the Sun,
270
00:16:36,210 --> 00:16:41,596
55 million light-years away
and we're looking at it.
271
00:16:41,620 --> 00:16:44,526
So when you look at
the image, it's totally fine.
272
00:16:44,550 --> 00:16:46,066
You're totally forgiven
for thinking,
273
00:16:46,090 --> 00:16:48,596
"ah, it looks a little blurry."
274
00:16:48,620 --> 00:16:52,066
But I cannot reiterate enough
275
00:16:52,090 --> 00:16:55,176
how profound
this image actually is.
276
00:16:55,200 --> 00:16:59,276
We are seeing just a hair's
width away from a discontinuity
277
00:16:59,300 --> 00:17:01,646
in the fabric
of space-time itself.
278
00:17:01,670 --> 00:17:05,516
Actually seeing so close
to an actual event horizon,
279
00:17:05,540 --> 00:17:07,956
a discontinuity in the fabric
of space-time,
280
00:17:07,980 --> 00:17:11,386
never seemed possible.
281
00:17:11,410 --> 00:17:14,956
This image of the
heart of a distant galaxy
282
00:17:14,980 --> 00:17:19,590
helps us understand supermassive
black holes like never before.
283
00:17:21,760 --> 00:17:24,336
When we observe
supermassive black holes
284
00:17:24,360 --> 00:17:26,706
in other galaxies,
including the one in m87,
285
00:17:26,730 --> 00:17:28,936
we're able to learn more about
the big picture
286
00:17:28,960 --> 00:17:32,676
of how these massive black holes
form and evolve over time.
287
00:17:32,700 --> 00:17:34,416
And that in turn,
helps us understand
288
00:17:34,440 --> 00:17:35,746
how our Milky Way galaxy
289
00:17:35,770 --> 00:17:38,270
and its super massive
black hole has formed.
290
00:17:40,440 --> 00:17:42,786
By studying, not just
making images of black holes,
291
00:17:42,810 --> 00:17:44,686
but making videos
of black holes,
292
00:17:44,710 --> 00:17:47,796
and seeing as that gas
is spinning around it,
293
00:17:47,820 --> 00:17:50,896
we can try to map around
a black hole more precisely
294
00:17:50,920 --> 00:17:52,890
and learn about its dynamics.
295
00:17:54,990 --> 00:17:57,366
An image of Sagittarius A-star
296
00:17:57,390 --> 00:17:58,766
remains out of reach,
297
00:17:58,790 --> 00:18:02,930
but in 2018, it shows
a deadly side to its character.
298
00:18:04,700 --> 00:18:07,316
The supermassive black
hole's accretion disk
299
00:18:07,340 --> 00:18:10,116
releases huge, powerful flares,
300
00:18:10,140 --> 00:18:13,810
and they could be pointed
right at us.
301
00:18:22,020 --> 00:18:26,566
In 2018, astronomers
were studying a special star
302
00:18:26,590 --> 00:18:29,806
orbiting our galaxy's
supermassive black hole.
303
00:18:29,830 --> 00:18:33,206
The star passes close
to Sagittarius A-star...
304
00:18:33,230 --> 00:18:35,636
every 16 years.
305
00:18:35,660 --> 00:18:40,276
It's called S2, and by studying
this star's fly-by,
306
00:18:40,300 --> 00:18:44,040
we hope to learn more
about Sagittarius A-star.
307
00:18:45,370 --> 00:18:48,216
We think that S2 may
be the very closest star
308
00:18:48,240 --> 00:18:51,656
to the supermassive black hole
in the center of our galaxy.
309
00:18:51,680 --> 00:18:53,756
At closest approach
to sag A-star,
310
00:18:53,780 --> 00:18:58,390
S2 comes within 17 light hours
or so of the surface.
311
00:19:00,920 --> 00:19:04,136
The supermassive black
hole's powerful gravity
312
00:19:04,160 --> 00:19:09,176
accelerates the star
to 17 million miles an hour.
313
00:19:09,200 --> 00:19:12,516
That's fast enough to travel
from New York to L.A.
314
00:19:12,540 --> 00:19:15,616
In half a second,
315
00:19:15,640 --> 00:19:19,370
but it's not the star's speed
that excites scientists.
316
00:19:20,410 --> 00:19:23,186
This is a great star, because
it's on an elliptical orbit
317
00:19:23,210 --> 00:19:25,756
that takes it fairly far
from the black hole,
318
00:19:25,780 --> 00:19:27,056
but every few years,
319
00:19:27,080 --> 00:19:30,650
it passes right above
the supermassive black hole.
320
00:19:32,720 --> 00:19:36,936
As we tracked S2's
swing around Sagittarius A-star,
321
00:19:36,960 --> 00:19:40,506
we detected powerful
bursts of infrared light
322
00:19:40,530 --> 00:19:44,200
coming from the direction
of the supermassive black hole.
323
00:19:46,670 --> 00:19:48,316
There's a blob of gas
324
00:19:48,340 --> 00:19:51,016
that is orbiting very close
to the black hole,
325
00:19:51,040 --> 00:19:53,556
and it was flaring
as it went around.
326
00:19:53,580 --> 00:19:55,716
There were three separate
flares of light
327
00:19:55,740 --> 00:19:59,056
that they were able to detect.
328
00:19:59,080 --> 00:20:00,956
The flares didn't come directly
329
00:20:00,980 --> 00:20:04,426
from
the supermassive black hole,
330
00:20:04,450 --> 00:20:07,690
they came from
the material around it.
331
00:20:10,230 --> 00:20:12,776
The flares that were discovered
are thought to originate
332
00:20:12,800 --> 00:20:14,276
from magnetic storms
333
00:20:14,300 --> 00:20:18,500
in this very, very hot turbulent
gas around the black hole.
334
00:20:20,900 --> 00:20:23,246
The extreme heat
in the accretion disk
335
00:20:23,270 --> 00:20:26,386
strips electrons
from atoms of gas.
336
00:20:26,410 --> 00:20:30,256
The stripped electrons
and hot gas form a plasma,
337
00:20:30,280 --> 00:20:32,956
which creates powerful
magnetic fields
338
00:20:32,980 --> 00:20:35,280
when accelerated to high speeds.
339
00:20:37,250 --> 00:20:39,496
Because some super
massive black holes
340
00:20:39,520 --> 00:20:40,796
have these superheated,
341
00:20:40,820 --> 00:20:44,166
rapidly spinning vortices
of gas swirling around them,
342
00:20:44,190 --> 00:20:46,206
you get these very,
very powerful,
343
00:20:46,230 --> 00:20:48,560
very tightly wound
magnetic fields.
344
00:20:50,630 --> 00:20:52,746
And there's energy stored
in that magnetic field.
345
00:20:52,770 --> 00:20:55,676
It's like a bunch of piano wires
all tangled up.
346
00:20:55,700 --> 00:20:58,586
And if these things interact
with each other, they can snap,
347
00:20:58,610 --> 00:21:01,240
and when they snap,
that energy is released.
348
00:21:05,450 --> 00:21:07,696
You'll get this
enormous release of energy
349
00:21:07,720 --> 00:21:11,266
as these coils of magnetic
fields effectively snap.
350
00:21:11,290 --> 00:21:15,896
And when they do so, just like
on the surface of our sun,
351
00:21:15,920 --> 00:21:18,560
they release
an enormous flare of gas.
352
00:21:22,160 --> 00:21:27,376
These powerful flares
can be millions of miles wide
353
00:21:27,400 --> 00:21:31,640
and come packed with superheated
gas and plasma.
354
00:21:35,210 --> 00:21:37,986
Solar flares release
as much energy
355
00:21:38,010 --> 00:21:40,710
as 10 million volcanic
explosions.
356
00:21:45,590 --> 00:21:50,506
Flares from Sagittarius
A-star's accretion disk
357
00:21:50,530 --> 00:21:55,600
are like millions of solar
flares all going off at once.
358
00:21:58,330 --> 00:22:02,000
It's kind of like comparing a
nuclear weapon to a firecracker.
359
00:22:04,140 --> 00:22:06,856
Sagittarius A-star's flares
360
00:22:06,880 --> 00:22:09,526
release intense blasts
of radiation,
361
00:22:09,550 --> 00:22:12,556
but by watching the flares
from Earth,
362
00:22:12,580 --> 00:22:14,526
we can learn about
the orientation
363
00:22:14,550 --> 00:22:17,620
of the supermassive
black hole's accretion disk.
364
00:22:19,390 --> 00:22:21,466
This gas that's in
this accretion disk
365
00:22:21,490 --> 00:22:25,236
around the black hole
is like a friendly helper
366
00:22:25,260 --> 00:22:27,376
shining a flashlight
back toward Earth.
367
00:22:27,400 --> 00:22:29,776
And we can watch the orbit
of these flashlights
368
00:22:29,800 --> 00:22:32,106
and help understand
the orientation of gas
369
00:22:32,130 --> 00:22:33,900
that swirls
around the black hole.
370
00:22:37,470 --> 00:22:39,416
We think we're getting
a bird's-eye view of it.
371
00:22:39,440 --> 00:22:41,086
And looking down the barrel,
372
00:22:41,110 --> 00:22:45,586
we're looking at the accretion
disk basically face-on.
373
00:22:45,610 --> 00:22:48,126
That means that any material
that gets blasted away
374
00:22:48,150 --> 00:22:50,980
from the black hole
could be aimed right at us.
375
00:22:53,990 --> 00:22:57,490
Should we be worried
about the flares reaching Earth?
376
00:22:59,090 --> 00:23:01,236
It sounds worrisome,
this blob of gas
377
00:23:01,260 --> 00:23:03,476
emitting these
huge flares of light,
378
00:23:03,500 --> 00:23:07,246
but you've got to realize,
this is 26,000 light-years away.
379
00:23:07,270 --> 00:23:08,546
That is a long way.
380
00:23:08,570 --> 00:23:11,116
It took an extremely sensitive
detector
381
00:23:11,140 --> 00:23:13,816
on one of the largest
telescopes on Earth
382
00:23:13,840 --> 00:23:16,726
to be able to see this at all.
383
00:23:16,750 --> 00:23:18,986
Earth is safe for now,
384
00:23:19,010 --> 00:23:22,196
but the more we learn
about the galaxy center,
385
00:23:22,220 --> 00:23:25,126
the more terrifying it becomes.
386
00:23:25,150 --> 00:23:27,236
We know of Sagittarius A-star,
387
00:23:27,260 --> 00:23:29,196
the central supermassive
black hole,
388
00:23:29,220 --> 00:23:31,006
but now we're beginning
to suspect
389
00:23:31,030 --> 00:23:33,590
that it might not be alone.
390
00:23:35,230 --> 00:23:37,806
A dangerous swarm of black holes
391
00:23:37,830 --> 00:23:41,716
could be racing around
the center of the Milky Way.
392
00:23:41,740 --> 00:23:44,940
Thousands more may
be hiding from sight.
393
00:23:53,720 --> 00:23:57,596
The supermassive black
hole, Sagittarius A-star,
394
00:23:57,620 --> 00:24:00,090
dominates the center
of the Milky Way...
395
00:24:02,120 --> 00:24:04,060
...affecting star formation...
396
00:24:06,230 --> 00:24:09,400
...and carving out vast
gas bubbles in space.
397
00:24:11,770 --> 00:24:16,546
But Sagittarius A-star might not
be the only black hole in town,
398
00:24:16,570 --> 00:24:19,440
or even the most dangerous.
399
00:24:21,840 --> 00:24:23,026
We've known for a long time
400
00:24:23,050 --> 00:24:24,456
that there's a supermassive
black hole
401
00:24:24,480 --> 00:24:26,356
in the very heart of our galaxy,
402
00:24:26,380 --> 00:24:29,526
but there may be an angry swarm
of smaller black holes,
403
00:24:29,550 --> 00:24:32,296
buzzing all around it.
404
00:24:32,320 --> 00:24:34,596
In April of 2018,
405
00:24:34,620 --> 00:24:37,306
astronomers led
by Columbia university
406
00:24:37,330 --> 00:24:39,836
revealed the results
of a hunting mission
407
00:24:39,860 --> 00:24:42,006
in the center of the galaxy.
408
00:24:42,030 --> 00:24:45,776
They'd used 12 years
of Chandra observatory data
409
00:24:45,800 --> 00:24:49,986
to seek out
stellar mass black holes.
410
00:24:50,010 --> 00:24:52,586
Black holes that are made
from the death of stars,
411
00:24:52,610 --> 00:24:54,216
from supernova explosions,
412
00:24:54,240 --> 00:24:56,940
are called stellar
mass black holes.
413
00:25:02,120 --> 00:25:04,066
And these are made from stars
414
00:25:04,090 --> 00:25:06,890
that were many times
the mass of the sun.
415
00:25:09,730 --> 00:25:14,336
Finding stellar mass
black holes is tough.
416
00:25:14,360 --> 00:25:17,376
Light can't escape
a black hole's gravity,
417
00:25:17,400 --> 00:25:19,400
so we can't see them directly.
418
00:25:22,700 --> 00:25:26,916
And stellar mass black holes
are only tens of miles wide,
419
00:25:26,940 --> 00:25:30,040
making them almost impossible
to detect.
420
00:25:32,280 --> 00:25:34,696
So astronomers look
for a special type
421
00:25:34,720 --> 00:25:36,680
of stellar mass black hole.
422
00:25:40,360 --> 00:25:44,266
One of the ways that we look
for stellar mass black holes,
423
00:25:44,290 --> 00:25:50,060
is that they often are vampires
eating a companion star.
424
00:25:53,800 --> 00:25:58,186
These vampires are
part of a binary pair,
425
00:25:58,210 --> 00:26:02,556
a stellar mass black hole
in orbit with a living star,
426
00:26:02,580 --> 00:26:05,950
the black hole feasting
on its partner.
427
00:26:07,380 --> 00:26:08,726
That black hole
428
00:26:08,750 --> 00:26:11,466
is like a very, very deadly
parasite for that star.
429
00:26:11,490 --> 00:26:14,266
It is ripping mass
off the surface of that star,
430
00:26:14,290 --> 00:26:17,660
and that matter is raining down
toward the black hole itself.
431
00:26:21,000 --> 00:26:23,046
And that material lights up,
432
00:26:23,070 --> 00:26:25,606
so this allows us
to hunt for black holes,
433
00:26:25,630 --> 00:26:28,676
not through taking pictures
of black holes directly,
434
00:26:28,700 --> 00:26:32,986
but through seeing the material
falling to its doom.
435
00:26:33,010 --> 00:26:35,056
The problem is,
436
00:26:35,080 --> 00:26:37,386
gas and dust spread
throughout the galaxy
437
00:26:37,410 --> 00:26:41,596
stops visible light from
the binary pair reaching Earth.
438
00:26:41,620 --> 00:26:44,696
But the binary pair release
another type of light
439
00:26:44,720 --> 00:26:48,796
that passes through the gas
and dust more easily...
440
00:26:48,820 --> 00:26:50,736
X-rays.
441
00:26:50,760 --> 00:26:53,276
The system itself
is emitting X-rays,
442
00:26:53,300 --> 00:26:55,276
so they're called
X-ray binaries.
443
00:26:55,300 --> 00:26:57,946
So these are useful,
because the X-ray emission
444
00:26:57,970 --> 00:26:59,446
can be very powerful
445
00:26:59,470 --> 00:27:02,146
and can be potentially seen
from the Earth,
446
00:27:02,170 --> 00:27:04,216
even though the binary
is very far away,
447
00:27:04,240 --> 00:27:06,040
say, at the galactic center.
448
00:27:08,640 --> 00:27:12,386
The glowing disks of
material in X-ray binary systems
449
00:27:12,410 --> 00:27:15,996
are almost a million times
smaller than the accretion disk
450
00:27:16,020 --> 00:27:19,326
surrounding Sagittarius A-star,
too small
451
00:27:19,350 --> 00:27:23,560
for us to see the material
swirling around them in detail.
452
00:27:25,060 --> 00:27:30,460
So, we see the X-ray binaries
as pinpricks of X-ray light.
453
00:27:33,200 --> 00:27:36,786
Astronomers detect
12 of these X-ray binaries
454
00:27:36,810 --> 00:27:40,356
in a small 3-light-year-wide
patch of space
455
00:27:40,380 --> 00:27:42,186
at the galactic center.
456
00:27:42,210 --> 00:27:44,756
And that means that there could
be a much larger collection
457
00:27:44,780 --> 00:27:47,756
of these relatively tiny stellar
mass black holes
458
00:27:47,780 --> 00:27:51,266
in the heart of our galaxy.
459
00:27:51,290 --> 00:27:53,666
If black holes form the way
we think they do,
460
00:27:53,690 --> 00:27:56,436
there very likely
may be swarms of black holes
461
00:27:56,460 --> 00:27:58,560
racing around
Sagittarius A-star.
462
00:28:01,500 --> 00:28:04,446
But X-ray binaries
that are powerful enough for us
463
00:28:04,470 --> 00:28:08,846
to detect are incredibly rare.
464
00:28:08,870 --> 00:28:13,586
So we estimate that for the
dozen X-ray binaries discovered,
465
00:28:13,610 --> 00:28:15,540
there could be up
to a thousand more.
466
00:28:20,820 --> 00:28:25,526
In total, there could be
20,000 stellar mass black holes
467
00:28:25,550 --> 00:28:28,690
in this 3-light-year
region of space.
468
00:28:38,070 --> 00:28:41,846
Why are these black holes
swarming in the galaxy center?
469
00:28:41,870 --> 00:28:45,810
It appears they've migrated
from the rest of the Milky Way.
470
00:28:47,340 --> 00:28:49,356
Through a process
called dynamical friction,
471
00:28:49,380 --> 00:28:51,856
black holes can actually sink
to the centers of galaxies
472
00:28:51,880 --> 00:28:55,926
very, very rapidly, like
dropping a stone into a pond.
473
00:28:55,950 --> 00:28:58,096
What that means
is that an errant,
474
00:28:58,120 --> 00:28:59,996
wandering black hole
might eventually
475
00:29:00,020 --> 00:29:02,596
find its way toward the center
of our own galaxy,
476
00:29:02,620 --> 00:29:06,576
where Sagittarius A-star
resides.
477
00:29:06,600 --> 00:29:10,606
As stellar mass black
holes orbit the galaxy,
478
00:29:10,630 --> 00:29:12,676
they interact gravitationally
479
00:29:12,700 --> 00:29:15,600
with stars and clouds
of gas and dust.
480
00:29:17,410 --> 00:29:20,516
These interactions
push the black holes
481
00:29:20,540 --> 00:29:23,826
towards the center
of the galaxy,
482
00:29:23,850 --> 00:29:25,450
where the black holes swarm.
483
00:29:30,390 --> 00:29:34,466
A swarm of stellar mass
black holes sounds deadly,
484
00:29:34,490 --> 00:29:37,006
but it may not be
the most lethal thing
485
00:29:37,030 --> 00:29:38,860
in the center of the Milky Way.
486
00:29:41,330 --> 00:29:45,376
A surprising observation
indicates that there is a lot
487
00:29:45,400 --> 00:29:49,376
of antimatter
in the center of our galaxy.
488
00:29:49,400 --> 00:29:52,516
And when antimatter
meets matter,
489
00:29:52,540 --> 00:29:55,240
the results are explosive.
490
00:30:05,620 --> 00:30:07,436
In 2017,
491
00:30:07,460 --> 00:30:11,890
astronomers tried to solve
a decades-old cosmic mystery...
492
00:30:14,830 --> 00:30:17,746
...unexplained
high-energy radiation
493
00:30:17,770 --> 00:30:19,700
streaming through our galaxy.
494
00:30:23,440 --> 00:30:25,940
At first, we didn't know
where it was from.
495
00:30:28,440 --> 00:30:31,226
But we discovered
it was gamma radiation
496
00:30:31,250 --> 00:30:34,950
coming from somewhere
in the center of the Milky Way.
497
00:30:37,550 --> 00:30:40,236
The question is,
what's making these gamma rays?
498
00:30:40,260 --> 00:30:41,966
That's hard to do.
499
00:30:41,990 --> 00:30:43,506
It's not like
you can rub your hands together
500
00:30:43,530 --> 00:30:46,906
and generate gamma rays.
501
00:30:46,930 --> 00:30:48,976
When we took a closer
look at the gamma rays,
502
00:30:49,000 --> 00:30:52,776
we discovered the signature
of the most explosive substance
503
00:30:52,800 --> 00:30:55,440
in the universe... antimatter.
504
00:30:59,270 --> 00:31:02,556
Antimatter is like normal matter
505
00:31:02,580 --> 00:31:04,556
but with opposite charge.
506
00:31:04,580 --> 00:31:07,050
That's it.
It's matter's evil twin.
507
00:31:09,150 --> 00:31:11,926
When evil twin meets good twin,
508
00:31:11,950 --> 00:31:14,420
it is not a happy reunion.
509
00:31:17,330 --> 00:31:18,736
Antimatter is scary.
510
00:31:18,760 --> 00:31:21,436
It's not like you want
to have some in your kitchen.
511
00:31:21,460 --> 00:31:23,646
This stuff is very,
very explosive,
512
00:31:23,670 --> 00:31:25,746
if you want to think
of it that way.
513
00:31:25,770 --> 00:31:27,476
If it touches normal matter,
514
00:31:27,500 --> 00:31:29,800
it releases a huge
amount of energy.
515
00:31:31,740 --> 00:31:33,756
When matter
and antimatter combine,
516
00:31:33,780 --> 00:31:36,156
they annihilate each other
and transform
517
00:31:36,180 --> 00:31:39,656
into high-energy radiation,
just like the gamma rays
518
00:31:39,680 --> 00:31:42,780
seen streaming out
of the center of the Milky Way.
519
00:31:44,620 --> 00:31:47,536
We see antimatter
throughout the galaxy,
520
00:31:47,560 --> 00:31:49,966
but strangely,
the galactic center
521
00:31:49,990 --> 00:31:54,530
seemed to have 40% more
antimatter than anywhere else.
522
00:31:56,830 --> 00:31:58,646
Right now in the heart
of our galaxy,
523
00:31:58,670 --> 00:32:01,676
we actually observe
fountains of antimatter
524
00:32:01,700 --> 00:32:04,646
that are producing
10 trillion tons
525
00:32:04,670 --> 00:32:07,816
of antimatter every second.
526
00:32:07,840 --> 00:32:09,516
One of the big questions
that we've wondered about
527
00:32:09,540 --> 00:32:12,450
for a very long time, is what's
the origin of this stuff?
528
00:32:15,820 --> 00:32:19,396
Initially,
there were several suspects.
529
00:32:19,420 --> 00:32:21,166
One possible source
of antimatter
530
00:32:21,190 --> 00:32:24,806
is the central black hole,
Sagittarius A-star.
531
00:32:24,830 --> 00:32:26,436
Matter can be swirling
around this
532
00:32:26,460 --> 00:32:28,176
and it can have such high energy
533
00:32:28,200 --> 00:32:29,960
that it can create antimatter.
534
00:32:33,230 --> 00:32:34,916
But the antimatter
535
00:32:34,940 --> 00:32:37,046
isn't coming
from a single point,
536
00:32:37,070 --> 00:32:41,556
it's spread across thousands
of light-years of space.
537
00:32:41,580 --> 00:32:43,216
So Sagittarius A-star
538
00:32:43,240 --> 00:32:46,750
can't be the source
of the gamma-ray stream.
539
00:32:49,680 --> 00:32:52,590
Another suspect was dark matter.
540
00:32:55,060 --> 00:32:56,566
One of the biggest mysteries
in the universe
541
00:32:56,590 --> 00:32:58,636
right now is dark matter.
542
00:32:58,660 --> 00:33:01,506
We know that the majority
of mass in the universe
543
00:33:01,530 --> 00:33:03,136
is not in the same form
that we are.
544
00:33:03,160 --> 00:33:04,906
It's not made of atoms,
545
00:33:04,930 --> 00:33:07,446
but whatever sort of particle
it is or may be,
546
00:33:07,470 --> 00:33:10,846
if these things collide,
they can produce antimatter,
547
00:33:10,870 --> 00:33:12,586
and that will produce
the gamma rays.
548
00:33:12,610 --> 00:33:15,216
So it's possible that as we look
into the heart of the galaxy
549
00:33:15,240 --> 00:33:17,026
and see these extra gamma rays,
550
00:33:17,050 --> 00:33:19,650
that's the signal
that dark matter is there.
551
00:33:23,690 --> 00:33:26,736
But the gamma ray
stream we detected is too weak
552
00:33:26,760 --> 00:33:29,160
to have been created
by dark matter.
553
00:33:31,830 --> 00:33:35,676
Then we had a breakthrough.
554
00:33:35,700 --> 00:33:40,316
We discovered that a special
metal called titanium-44
555
00:33:40,340 --> 00:33:43,500
could be responsible
for the gamma-ray stream.
556
00:33:47,340 --> 00:33:50,526
Titanium-44 is a highly
radioactive element.
557
00:33:50,550 --> 00:33:52,226
That means that
it wants to decay
558
00:33:52,250 --> 00:33:54,080
into other types of nuclei.
559
00:33:57,090 --> 00:33:59,626
When titanium-44 decays,
560
00:33:59,650 --> 00:34:01,436
it gives off antimatter.
561
00:34:01,460 --> 00:34:05,666
But to produce the antimatter
seen in the galaxy's core,
562
00:34:05,690 --> 00:34:09,106
you would need
a lot of titanium-44.
563
00:34:09,130 --> 00:34:14,216
It could be created
in rare energetic events,
564
00:34:14,240 --> 00:34:18,670
in the collision of two dead
stars... white dwarfs.
565
00:34:20,580 --> 00:34:23,386
A white dwarf star is a star
that didn't have enough mass
566
00:34:23,410 --> 00:34:25,986
when it died
to actually become a supernova.
567
00:34:26,010 --> 00:34:28,656
It just sort of cools off
as a dead little cinder.
568
00:34:28,680 --> 00:34:30,326
But what if you have
two white dwarfs
569
00:34:30,350 --> 00:34:32,126
that are orbiting
around each other,
570
00:34:32,150 --> 00:34:34,936
and as they come closer
and closer and collide,
571
00:34:34,960 --> 00:34:36,906
all of a sudden now,
you have enough mass
572
00:34:36,930 --> 00:34:39,290
to actually kick
a supernova explosion off.
573
00:34:44,370 --> 00:34:46,176
These particular kinds
of supernovae
574
00:34:46,200 --> 00:34:49,070
are very good
at producing titanium-44.
575
00:34:50,870 --> 00:34:53,656
So these kinds of supernovas
are very, very good
576
00:34:53,680 --> 00:34:55,310
at making antimatter.
577
00:34:57,880 --> 00:35:00,856
These supernovas
erupt in the core of the galaxy
578
00:35:00,880 --> 00:35:03,220
once every 2,000 years.
579
00:35:06,220 --> 00:35:09,136
But outside of the core
in the disk of the galaxy
580
00:35:09,160 --> 00:35:11,390
where our solar system orbits...
581
00:35:13,530 --> 00:35:16,760
...these supernovas happen
three times as often.
582
00:35:18,330 --> 00:35:22,146
So the gamma ray observations
were wrong.
583
00:35:22,170 --> 00:35:25,846
There isn't more antimatter
in the heart of the galaxy.
584
00:35:25,870 --> 00:35:28,086
It's our region of the galaxy
585
00:35:28,110 --> 00:35:31,210
that contains
the most antimatter.
586
00:35:33,380 --> 00:35:36,150
Question is, are we in danger?
587
00:35:38,590 --> 00:35:39,766
If you take an ounce of matter
588
00:35:39,790 --> 00:35:41,736
and an ounce of antimatter
and collide them,
589
00:35:41,760 --> 00:35:45,166
you're generating
a megaton of energy,
590
00:35:45,190 --> 00:35:49,776
the equivalent of a million tons
of TNT exploding.
591
00:35:49,800 --> 00:35:51,746
So you don't need
much antimatter to generate
592
00:35:51,770 --> 00:35:54,676
a vast amount of energy.
593
00:35:54,700 --> 00:35:56,886
But the thing you have
to remember is we live
594
00:35:56,910 --> 00:35:59,146
in this wonderful,
dramatic environment
595
00:35:59,170 --> 00:36:00,356
of a larger universe.
596
00:36:00,380 --> 00:36:01,716
It's not dangerous.
597
00:36:01,740 --> 00:36:04,780
It's very far away from us,
and it's fascinating.
598
00:36:07,250 --> 00:36:10,566
But all of this antimatter
is being produced in our galaxy,
599
00:36:10,590 --> 00:36:13,620
so just sit back
and enjoy the fireworks.
600
00:36:15,890 --> 00:36:18,366
The center of the Milky Way
601
00:36:18,390 --> 00:36:19,866
is violent and extreme,
602
00:36:19,890 --> 00:36:22,830
but things could get
a whole lot worse.
603
00:36:24,700 --> 00:36:26,846
Rogue supermassive black holes
604
00:36:26,870 --> 00:36:30,046
could be
lurking near our galaxy,
605
00:36:30,070 --> 00:36:34,040
and they have the power
to end life as we know it.
606
00:36:45,220 --> 00:36:49,436
The Milky Way is around
100,000 light-years across,
607
00:36:49,460 --> 00:36:54,506
and it's home to at least
200 billion stars,
608
00:36:54,530 --> 00:36:58,046
but it hasn't
always been this large.
609
00:36:58,070 --> 00:37:01,416
We know that our Milky Way
galaxy grew to the size
610
00:37:01,440 --> 00:37:06,746
it is now, which is huge,
by eating other galaxies.
611
00:37:06,770 --> 00:37:09,056
And some of these galaxies
would've had
612
00:37:09,080 --> 00:37:11,580
supermassive black holes
in their centers.
613
00:37:14,220 --> 00:37:16,856
When the Milky Way's gravity
614
00:37:16,880 --> 00:37:18,666
pulled in smaller galaxies,
615
00:37:18,690 --> 00:37:23,806
most of their material
merged with the Milky Way,
616
00:37:23,830 --> 00:37:25,966
but some material like stars,
617
00:37:25,990 --> 00:37:29,436
could've been slung tens
of thousands of light-years
618
00:37:29,460 --> 00:37:31,100
out of the Milky Way.
619
00:37:33,400 --> 00:37:36,876
This could've happened
to a smaller galaxy's
620
00:37:36,900 --> 00:37:39,786
super massive black hole.
621
00:37:39,810 --> 00:37:41,456
It is entirely possible
622
00:37:41,480 --> 00:37:43,516
there are supermassive
black holes
623
00:37:43,540 --> 00:37:46,980
wandering around out there,
not in the center.
624
00:37:49,420 --> 00:37:51,196
So how could it be
possible that there's actually
625
00:37:51,220 --> 00:37:53,966
a supermassive black hole
close to us wandering around,
626
00:37:53,990 --> 00:37:55,736
but we never even see it?
627
00:37:55,760 --> 00:37:59,206
Well, remember black hole
means it's really, really black.
628
00:37:59,230 --> 00:38:02,036
It actually absorbs radiation
and any energy.
629
00:38:02,060 --> 00:38:04,476
So unless something is falling
into a black hole
630
00:38:04,500 --> 00:38:08,376
or orbiting around it,
you're not going to see it.
631
00:38:08,400 --> 00:38:09,946
And so, if this
supermassive black hole
632
00:38:09,970 --> 00:38:13,246
were hypothetically wandering
the outskirts of our galaxy,
633
00:38:13,270 --> 00:38:15,216
well, there's a lot less
gas there
634
00:38:15,240 --> 00:38:16,916
for that black hole to run into.
635
00:38:16,940 --> 00:38:18,126
And if there's no gas around
636
00:38:18,150 --> 00:38:20,550
that black hole,
we will not see it.
637
00:38:22,680 --> 00:38:26,096
The rogue supermassive
black hole may not stay
638
00:38:26,120 --> 00:38:28,996
in the outskirts
of the galaxy forever.
639
00:38:29,020 --> 00:38:32,636
Gravitational interactions
slowly pull it back
640
00:38:32,660 --> 00:38:34,636
into the Milky Way.
641
00:38:34,660 --> 00:38:36,436
Billions of years later,
642
00:38:36,460 --> 00:38:41,230
the supermassive black hole
could arrive in the center.
643
00:38:45,570 --> 00:38:48,686
When this rogue supermassive
black hole meets up with
644
00:38:48,710 --> 00:38:53,550
Sagittarius A-star,
the fuse is lit.
645
00:38:55,180 --> 00:38:57,650
The pair spiral
towards each other...
646
00:39:00,920 --> 00:39:02,866
...spinning faster and faster,
647
00:39:02,890 --> 00:39:05,460
reaching up to half
the speed of light.
648
00:39:10,700 --> 00:39:14,530
Finally,
the two black holes merge.
649
00:39:20,810 --> 00:39:21,986
You would have
650
00:39:22,010 --> 00:39:24,156
an enormously energetic event
on your hands.
651
00:39:24,180 --> 00:39:26,656
Those supermassive black holes
could, in principle,
652
00:39:26,680 --> 00:39:30,526
merge together, create a huge
blast of gravitational waves,
653
00:39:30,550 --> 00:39:34,366
accompanied by a profoundly
energetic flash of light
654
00:39:34,390 --> 00:39:37,060
that could, in principle,
endanger all life on Earth.
655
00:39:43,160 --> 00:39:45,646
It's literally a stretching
656
00:39:45,670 --> 00:39:47,816
and contracting of space itself.
657
00:39:47,840 --> 00:39:50,046
It's like grabbing
the framework of space
658
00:39:50,070 --> 00:39:51,916
and it's shaking it really hard.
659
00:39:51,940 --> 00:39:53,886
And if this happens
in our galaxy,
660
00:39:53,910 --> 00:39:59,040
the amount of energy emitted,
that would be bad.
661
00:40:01,120 --> 00:40:03,296
When the black holes collide,
662
00:40:03,320 --> 00:40:04,626
they release more energy
663
00:40:04,650 --> 00:40:08,690
than all the stars
in the galaxy combined.
664
00:40:15,500 --> 00:40:17,846
Should we be panicked
about this?
665
00:40:17,870 --> 00:40:19,246
And the answer is no.
666
00:40:19,270 --> 00:40:21,176
The Earth has been orbiting
the sun
667
00:40:21,200 --> 00:40:23,886
for 4 1/2 billion years
without any incident, right?
668
00:40:23,910 --> 00:40:26,516
We're pretty safe from them.
669
00:40:26,540 --> 00:40:30,656
If we were around to
see the two black holes collide,
670
00:40:30,680 --> 00:40:33,386
we'd witness the most
destructive light show
671
00:40:33,410 --> 00:40:35,350
in the history of the galaxy.
672
00:40:38,020 --> 00:40:43,336
But for now, the center of our
galaxy is relatively quiet,
673
00:40:43,360 --> 00:40:46,390
but it's still
a terrible place to be.
674
00:40:49,930 --> 00:40:53,046
The center of our Milky Way
is not a friendly place.
675
00:40:53,070 --> 00:40:56,816
It's nowhere you want to be.
It's a bad neighborhood.
676
00:40:56,840 --> 00:41:00,916
You've got tons of stars,
tons of radiation,
677
00:41:00,940 --> 00:41:05,026
and stars are being born
and dying and exploding.
678
00:41:05,050 --> 00:41:06,886
You've got the central
supermassive black hole.
679
00:41:06,910 --> 00:41:09,556
You've got a potential swarm
of black holes.
680
00:41:09,580 --> 00:41:11,996
You've got accretion disks.
You've got flares.
681
00:41:12,020 --> 00:41:16,096
You've got magnetic outbursts.
You've got jets.
682
00:41:16,120 --> 00:41:18,690
Let's just stay out here
in the suburbs, all right?
683
00:41:20,830 --> 00:41:22,136
The center of our galaxy
684
00:41:22,160 --> 00:41:25,830
is one of the most nightmarish
places in the cosmos.
685
00:41:28,640 --> 00:41:32,016
It's also home to some
of the most incredible forces
686
00:41:32,040 --> 00:41:33,740
the universe has to offer.
687
00:41:36,540 --> 00:41:39,210
Whatever the future
holds for our galaxy...
688
00:41:41,620 --> 00:41:46,866
...the core of the Milky Way
will be at the center of it all.
689
00:41:46,890 --> 00:41:50,396
Our home galaxy, the Milky Way,
is our safe harbor,
690
00:41:50,420 --> 00:41:53,766
our island in this vast,
cosmic ocean.
691
00:41:53,790 --> 00:41:56,776
And so to understand
the heart of our galaxy,
692
00:41:56,800 --> 00:42:00,530
is to understand our home
in this cosmic void.