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Narrator:
 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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             Plait:
    Gas streaming everywhere,

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     radiation blasting out,

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    stars moving willy-nilly.

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 Thaller: 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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  Narrator: 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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     Narrator: Understanding
    the center of our galaxy

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   unlock secrets of our past,
       present and future.

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--<font color="
www.Vitac.Com

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captions paid for by
discovery communications

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♪

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♪

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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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♪

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  the columns seem to be coming
    from sagittarius a-star.

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           Filippenko:
  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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 Narrator: 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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 Narrator: 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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            Tremblay:
  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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Narrator: 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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            Narrator:
   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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  Narrator: 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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   Narrator: 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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                     ♪

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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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            Narrator:
      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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            Narrator:
    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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Narrator: The jets left
   destruction in their wake.

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                     ♪

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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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     Tremblay: 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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                     ♪

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            narrator:
 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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Thaller: 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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    Narrator: 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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  Tremblay: 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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 Narrator: 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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                     ♪

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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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 Sutter: 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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  Narrator: 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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                     ♪

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            narrator:
   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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           Filippenko:
     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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     Narrator: 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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            Tremblay:
 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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Narrator: 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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Narrator: 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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             Plait:
   Sagittarius a-star is big,

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00:12:29,349 --> 00:12:32,250
            but it's
    26,000 light-years away.

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00:12:32,252 --> 00:12:34,719
       A single light-year
is 6 trillion miles.

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00:12:34,721 --> 00:12:36,821
  So this is a long, long walk.

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00:12:36,823 --> 00:12:38,690
    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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 Narrator: To see the tiny dot,

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00:12:47,968 --> 00:12:51,803
       we need a telescope
     the size of the earth.

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00:12:51,805 --> 00:12:52,904
  How do you possibly do that?

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00:12:52,906 --> 00:12:56,474
         You can't build
     that telescope, right?

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00:12:56,476 --> 00:12:57,575
     Well, there's a trick.

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00:12:57,577 --> 00:12:59,244
        You actually get
   a few different telescopes

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00:12:59,246 --> 00:13:02,413
     and you spread them out
over the surface of the earth.

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00:13:02,415 --> 00:13:08,052
                     ♪

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00:13:08,054 --> 00:13:11,523
    doeleman: And when we had
  all of these sites together,

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00:13:11,525 --> 00:13:14,626
      we wind up being able
  to take an image of something

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00:13:14,628 --> 00:13:18,930
         that is really,
    really impossibly small.

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00:13:18,932 --> 00:13:22,300
Narrator: To gather enough light
   to see a target this small,

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00:13:22,302 --> 00:13:25,103
          the team take
      long-exposure images

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00:13:25,105 --> 00:13:27,906
     of sagittarius a-star's
            shadow...

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00:13:31,711 --> 00:13:34,579
    ...But there's a problem.

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00:13:34,581 --> 00:13:37,382
    The accretion disk moves
         too much for us

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00:13:37,384 --> 00:13:39,384
to capture a clear image.

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       When you're taking
  a long exposure of a person,

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00:13:44,691 --> 00:13:46,157
             right,
   you need them to be really,

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00:13:46,159 --> 00:13:47,926
      really still, right?

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00:13:47,928 --> 00:13:49,494
Because if they're moving around
             a lot,

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00:13:49,496 --> 00:13:51,362
      they're going to blur
         the image out.

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00:13:51,364 --> 00:13:52,831
     And that kind of thing
          is happening

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00:13:52,833 --> 00:13:54,833
         when we observe
       sagittarius a-star

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00:13:54,835 --> 00:13:57,235
     because it is unwilling
      to sit still for us.

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00:13:57,237 --> 00:13:58,937
    It is booming and banging
          and flashing

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00:13:58,939 --> 00:14:03,174
on the timescale
       of literally hours.

239
00:14:03,176 --> 00:14:06,311
  Narrator: As glowing material
      orbits the black hole

240
00:14:06,313 --> 00:14:07,912
   at 30% the speed of light,

241
00:14:07,914 --> 00:14:11,416
      sagittarius a-star's
          shadow blurs.

242
00:14:13,820 --> 00:14:16,120
Future developments may allow us

243
00:14:16,122 --> 00:14:18,790
    to see sagittarius a-star
            clearly.

244
00:14:21,561 --> 00:14:24,429
    For now, we can't capture
        an accurate image

245
00:14:24,431 --> 00:14:27,265
         of our galaxy's
    supermassive black hole.

246
00:14:30,070 --> 00:14:33,404
       But the hunt to see
    a supermassive black hole

247
00:14:33,406 --> 00:14:34,839
          wasn't over.

248
00:14:34,841 --> 00:14:38,676
The event horizon telescope
    turned to another galaxy

249
00:14:38,678 --> 00:14:43,548
           54 million
    light-years away -- m87.

250
00:14:44,985 --> 00:14:48,086
    M87 is an absolute beast
          of a galaxy.

251
00:14:48,088 --> 00:14:50,221
       It's the so-called
    brightest cluster galaxy.

252
00:14:50,223 --> 00:14:52,991
   These are among the largest
    galaxies in the universe.

253
00:14:55,028 --> 00:14:56,895
    Narrator: And m87 is home

254
00:14:56,897 --> 00:14:59,764
     to another supermassive
          black hole --

255
00:14:59,766 --> 00:15:02,800
       the giant m87 star.

256
00:15:04,237 --> 00:15:09,607
     M87 star is so massive
  that the gravitational region

257
00:15:09,609 --> 00:15:12,176
       that's interesting
is actually easier to image

258
00:15:12,178 --> 00:15:14,579
       than the black hole
       in our own galaxy.

259
00:15:17,651 --> 00:15:22,120
   Narrator: M87 star is over
  a thousand times more massive

260
00:15:22,122 --> 00:15:24,188
     than sagittarius a-star

261
00:15:24,190 --> 00:15:28,159
          and has a far
     larger accretion disk.

262
00:15:28,161 --> 00:15:31,496
When photographing a black hole,
          size matters,

263
00:15:31,498 --> 00:15:36,034
   because big accretion disks
   project more stable light,

264
00:15:36,036 --> 00:15:39,237
        so images of them
       don't blur as much.

265
00:15:42,242 --> 00:15:44,575
        In April of 2019,

266
00:15:44,577 --> 00:15:49,113
     the event horizon team
      unveiled their image.

267
00:15:49,115 --> 00:15:52,717
We have seen what we thought
         was unseeable.

268
00:15:52,719 --> 00:15:57,388
We have seen and taken a picture
        of a black hole.

269
00:15:57,390 --> 00:15:58,656
          [ applause ]

270
00:15:58,658 --> 00:16:05,229
                     ♪

271
00:16:05,231 --> 00:16:06,631
        I've been working
         on this project

272
00:16:06,633 --> 00:16:09,634
    for almost six years now,
    and so, this is something

273
00:16:09,636 --> 00:16:13,972
  we've been looking forward to
     for a really long time.

274
00:16:13,974 --> 00:16:16,607
 Narrator: Capturing this image
      took decades of work

275
00:16:16,609 --> 00:16:20,478
    by hundreds of scientists
       all over the world.

276
00:16:23,350 --> 00:16:25,783
 Galison: I was really stunned.

277
00:16:25,785 --> 00:16:29,721
Suddenly, when you say that's
 the real thing, that's amazing.

278
00:16:29,723 --> 00:16:31,489
     It really affected me.

279
00:16:31,491 --> 00:16:34,525
        This is something
       6 1/2 billion times

280
00:16:34,527 --> 00:16:36,194
      the mass of the sun,

281
00:16:36,196 --> 00:16:41,599
   55 million light-years away
    and we're looking at it.

282
00:16:41,601 --> 00:16:44,535
  Tremblay: So when you look at
  the image, it's totally fine.

283
00:16:44,537 --> 00:16:46,070
     You're totally forgiven
          for thinking,

284
00:16:46,072 --> 00:16:48,606
 "ah, it looks a little blurry."

285
00:16:48,608 --> 00:16:52,076
  but I cannot reiterate enough

286
00:16:52,078 --> 00:16:55,179
          how profound
     this image actually is.

287
00:16:55,181 --> 00:16:59,283
We are seeing just a hair's
 width away from a discontinuity

288
00:16:59,285 --> 00:17:01,652
          in the fabric
      of space-time itself.

289
00:17:01,654 --> 00:17:05,523
    Actually seeing so close
   to an actual event horizon,

290
00:17:05,525 --> 00:17:07,959
  a discontinuity in the fabric
         of space-time,

291
00:17:07,961 --> 00:17:11,396
     never seemed possible.

292
00:17:11,398 --> 00:17:14,966
   Narrator: This image of the
    heart of a distant galaxy

293
00:17:14,968 --> 00:17:19,570
helps us understand supermassive
 black holes like never before.

294
00:17:21,741 --> 00:17:24,342
    Straughn: When we observe
    supermassive black holes

295
00:17:24,344 --> 00:17:26,711
       in other galaxies,
including the one in m87,

296
00:17:26,713 --> 00:17:28,946
 we're able to learn more about
         the big picture

297
00:17:28,948 --> 00:17:32,683
of how these massive black holes
   form and evolve over time.

298
00:17:32,685 --> 00:17:34,419
        And that in turn,
       helps us understand

299
00:17:34,421 --> 00:17:35,753
    how our milky way galaxy

300
00:17:35,755 --> 00:17:38,256
      and its super massive
     black hole has formed.

301
00:17:40,427 --> 00:17:42,794
  Bouman: By studying, not just
  making images of black holes,

302
00:17:42,796 --> 00:17:44,695
        but making videos
         of black holes,

303
00:17:44,697 --> 00:17:47,799
     and seeing as that gas
     is spinning around it,

304
00:17:47,801 --> 00:17:50,902
we can try to map around
   a black hole more precisely

305
00:17:50,904 --> 00:17:52,870
  and learn about its dynamics.

306
00:17:54,974 --> 00:17:57,375
       Narrator: An image
      of sagittarius a-star

307
00:17:57,377 --> 00:17:58,776
      remains out of reach,

308
00:17:58,778 --> 00:18:02,914
      but in 2018, it shows
 a deadly side to its character.

309
00:18:04,684 --> 00:18:07,318
     The supermassive black
      hole's accretion disk

310
00:18:07,320 --> 00:18:10,121
 releases huge, powerful flares,

311
00:18:10,123 --> 00:18:13,791
    and they could be pointed
          right at us.

312
00:18:22,001 --> 00:18:26,571
 Narrator: In 2018, astronomers
  were studying a special star

313
00:18:26,573 --> 00:18:29,807
      orbiting our galaxy's
supermassive black hole.

314
00:18:29,809 --> 00:18:33,211
      The star passes close
    to sagittarius a-star --

315
00:18:33,213 --> 00:18:35,646
         every 16 years.

316
00:18:35,648 --> 00:18:40,284
 It's called s2, and by studying
       this star's fly-by,

317
00:18:40,286 --> 00:18:44,021
      we hope to learn more
    about sagittarius a-star.

318
00:18:45,358 --> 00:18:48,226
 Tremblay: We think that s2 may
    be the very closest star

319
00:18:48,228 --> 00:18:51,662
 to the supermassive black hole
  in the center of our galaxy.

320
00:18:51,664 --> 00:18:53,764
       At closest approach
         to sag a-star,

321
00:18:53,766 --> 00:18:58,369
 s2 comes within 17 light hours
      or so of the surface.

322
00:19:00,907 --> 00:19:04,142
Narrator: The supermassive black
     hole's powerful gravity

323
00:19:04,144 --> 00:19:09,180
      accelerates the star
  to 17 million miles an hour.

324
00:19:09,182 --> 00:19:12,517
  That's fast enough to travel
      from new york to l.A.

325
00:19:12,519 --> 00:19:15,620
        In half a second,

326
00:19:15,622 --> 00:19:19,357
  but it's not the star's speed
    that excites scientists.

327
00:19:20,393 --> 00:19:23,194
  This is a great star, because
   it's on an elliptical orbit

328
00:19:23,196 --> 00:19:25,763
    that takes it fairly far
      from the black hole,

329
00:19:25,765 --> 00:19:27,064
      but every few years,

330
00:19:27,066 --> 00:19:30,635
      it passes right above
  the supermassive black hole.

331
00:19:32,705 --> 00:19:36,941
Narrator: As we tracked s2's
swing around sagittarius a-star,

332
00:19:36,943 --> 00:19:40,511
      we detected powerful
    bursts of infrared light

333
00:19:40,513 --> 00:19:44,182
    coming from the direction
 of the supermassive black hole.

334
00:19:46,653 --> 00:19:48,319
             Plait:
      There's a blob of gas

335
00:19:48,321 --> 00:19:51,022
   that is orbiting very close
       to the black hole,

336
00:19:51,024 --> 00:19:53,558
       and it was flaring
       as it went around.

337
00:19:53,560 --> 00:19:55,726
    There were three separate
         flares of light

338
00:19:55,728 --> 00:19:59,063
 that they were able to detect.

339
00:19:59,065 --> 00:20:00,965
            Narrator:
 The flares didn't come directly

340
00:20:00,967 --> 00:20:04,435
from
  the supermassive black hole,

341
00:20:04,437 --> 00:20:07,672
         they came from
     the material around it.

342
00:20:10,210 --> 00:20:12,777
 The flares that were discovered
    are thought to originate

343
00:20:12,779 --> 00:20:14,278
      from magnetic storms

344
00:20:14,280 --> 00:20:18,482
in this very, very hot turbulent
   gas around the black hole.

345
00:20:20,887 --> 00:20:23,254
   Narrator: The extreme heat
      in the accretion disk

346
00:20:23,256 --> 00:20:26,390
        strips electrons
       from atoms of gas.

347
00:20:26,392 --> 00:20:30,261
     The stripped electrons
   and hot gas form a plasma,

348
00:20:30,263 --> 00:20:32,964
     which creates powerful
         magnetic fields

349
00:20:32,966 --> 00:20:35,266
when accelerated to high speeds.

350
00:20:37,237 --> 00:20:39,503
  Tremblay: Because some super
       massive black holes

351
00:20:39,505 --> 00:20:40,805
     have these superheated,

352
00:20:40,807 --> 00:20:44,175
    rapidly spinning vortices
  of gas swirling around them,

353
00:20:44,177 --> 00:20:46,210
       you get these very,
         very powerful,

354
00:20:46,212 --> 00:20:48,546
       very tightly wound
        magnetic fields.

355
00:20:50,617 --> 00:20:52,750
    And there's energy stored
     in that magnetic field.

356
00:20:52,752 --> 00:20:55,686
It's like a bunch of piano wires
         all tangled up.

357
00:20:55,688 --> 00:20:58,589
  And if these things interact
 with each other, they can snap,

358
00:20:58,591 --> 00:21:01,225
and when they snap,
    that energy is released.

359
00:21:05,431 --> 00:21:07,698
    Tremblay: You'll get this
   enormous release of energy

360
00:21:07,700 --> 00:21:11,269
   as these coils of magnetic
    fields effectively snap.

361
00:21:11,271 --> 00:21:15,906
 And when they do so, just like
   on the surface of our sun,

362
00:21:15,908 --> 00:21:18,542
          they release
    an enormous flare of gas.

363
00:21:22,148 --> 00:21:27,385
 Narrator: These powerful flares
  can be millions of miles wide

364
00:21:27,387 --> 00:21:31,622
and come packed with superheated
         gas and plasma.

365
00:21:35,194 --> 00:21:37,995
      Solar flares release
         as much energy

366
00:21:37,997 --> 00:21:40,698
as 10 million volcanic
           explosions.

367
00:21:40,700 --> 00:21:45,569
                     ♪

368
00:21:45,571 --> 00:21:50,508
     flares from sagittarius
     a-star's accretion disk

369
00:21:50,510 --> 00:21:55,579
   are like millions of solar
  flares all going off at once.

370
00:21:58,318 --> 00:22:01,986
  It's kind of like comparing a
nuclear weapon to a firecracker.

371
00:22:04,123 --> 00:22:06,857
            Narrator:
   Sagittarius a-star's flares

372
00:22:06,859 --> 00:22:09,527
     release intense blasts
          of radiation,

373
00:22:09,529 --> 00:22:12,563
   but by watching the flares
           from earth,

374
00:22:12,565 --> 00:22:14,532
       we can learn about
         the orientation

375
00:22:14,534 --> 00:22:17,601
of the supermassive
  black hole's accretion disk.

376
00:22:19,372 --> 00:22:21,472
  Tremblay: This gas that's in
       this accretion disk

377
00:22:21,474 --> 00:22:25,242
      around the black hole
    is like a friendly helper

378
00:22:25,244 --> 00:22:27,378
      shining a flashlight
       back toward earth.

379
00:22:27,380 --> 00:22:29,780
   And we can watch the orbit
      of these flashlights

380
00:22:29,782 --> 00:22:32,116
       and help understand
     the orientation of gas

381
00:22:32,118 --> 00:22:33,884
           that swirls
     around the black hole.

382
00:22:37,457 --> 00:22:39,423
     We think we're getting
    a bird's-eye view of it.

383
00:22:39,425 --> 00:22:41,092
  And looking down the barrel,

384
00:22:41,094 --> 00:22:45,596
we're looking at the accretion
     disk basically face-on.

385
00:22:45,598 --> 00:22:48,132
  That means that any material
     that gets blasted away

386
00:22:48,134 --> 00:22:50,968
       from the black hole
   could be aimed right at us.

387
00:22:53,973 --> 00:22:57,475
 Narrator: Should we be worried
about the flares reaching earth?

388
00:22:59,078 --> 00:23:01,245
   Plait: It sounds worrisome,
        this blob of gas

389
00:23:01,247 --> 00:23:03,481
         emitting these
      huge flares of light,

390
00:23:03,483 --> 00:23:07,251
   but you've got to realize,
this is 26,000 light-years away.

391
00:23:07,253 --> 00:23:08,552
       That is a long way.

392
00:23:08,554 --> 00:23:11,122
 It took an extremely sensitive
detector

393
00:23:11,124 --> 00:23:13,824
      on one of the largest
       telescopes on earth

394
00:23:13,826 --> 00:23:16,727
 to be able to see this at all.

395
00:23:16,729 --> 00:23:18,996
            Narrator:
     Earth is safe for now,

396
00:23:18,998 --> 00:23:22,199
      but the more we learn
    about the galaxy center,

397
00:23:22,201 --> 00:23:25,136
 the more terrifying it becomes.

398
00:23:25,138 --> 00:23:27,238
 We know of sagittarius a-star,

399
00:23:27,240 --> 00:23:29,206
    the central supermassive
           black hole,

400
00:23:29,208 --> 00:23:31,008
     but now we're beginning
           to suspect

401
00:23:31,010 --> 00:23:33,577
   that it might not be alone.

402
00:23:35,214 --> 00:23:37,815
            Narrator:
A dangerous swarm of black holes

403
00:23:37,817 --> 00:23:41,719
could be racing around
  the center of the milky way.

404
00:23:41,721 --> 00:23:44,922
       Thousands more may
      be hiding from sight.

405
00:23:47,960 --> 00:23:53,697
                     ♪

406
00:23:53,699 --> 00:23:57,601
narrator: The supermassive black
    hole, sagittarius a-star,

407
00:23:57,603 --> 00:24:00,070
      dominates the center
       of the milky way...

408
00:24:02,108 --> 00:24:04,041
 ...Affecting star formation...

409
00:24:06,212 --> 00:24:09,380
     ...And carving out vast
      gas bubbles in space.

410
00:24:11,751 --> 00:24:16,554
But sagittarius a-star might not
 be the only black hole in town,

411
00:24:16,556 --> 00:24:19,423
   or even the most dangerous.

412
00:24:21,828 --> 00:24:23,027
            Thaller:
We've known for a long time

413
00:24:23,029 --> 00:24:24,462
   that there's a supermassive
           black hole

414
00:24:24,464 --> 00:24:26,363
        in the very heart
         of our galaxy,

415
00:24:26,365 --> 00:24:29,533
 but there may be an angry swarm
     of smaller black holes,

416
00:24:29,535 --> 00:24:32,303
     buzzing all around it.

417
00:24:32,305 --> 00:24:34,605
   Narrator: In April of 2018,

418
00:24:34,607 --> 00:24:37,308
         astronomers led
     by columbia university

419
00:24:37,310 --> 00:24:39,844
      revealed the results
      of a hunting mission

420
00:24:39,846 --> 00:24:42,012
  in the center of the galaxy.

421
00:24:42,014 --> 00:24:45,783
      They'd used 12 years
   of chandra observatory data

422
00:24:45,785 --> 00:24:49,987
           to seek out
stellar mass black holes.

423
00:24:49,989 --> 00:24:52,590
    Black holes that are made
    from the death of stars,

424
00:24:52,592 --> 00:24:54,225
   from supernova explosions,

425
00:24:54,227 --> 00:24:56,927
       are called stellar
        mass black holes.

426
00:24:56,929 --> 00:25:02,099
                     ♪

427
00:25:02,101 --> 00:25:04,068
  and these are made from stars

428
00:25:04,070 --> 00:25:06,871
      that were many times
      the mass of the sun.

429
00:25:09,709 --> 00:25:14,345
 Narrator: Finding stellar mass
      black holes is tough.

430
00:25:14,347 --> 00:25:17,381
       Light can't escape
     a black hole's gravity,

431
00:25:17,383 --> 00:25:19,383
 so we can't see them directly.

432
00:25:22,688 --> 00:25:26,924
  And stellar mass black holes
are only tens of miles wide,

433
00:25:26,926 --> 00:25:30,027
  making them almost impossible
           to detect.

434
00:25:32,265 --> 00:25:34,698
       So astronomers look
       for a special type

435
00:25:34,700 --> 00:25:36,667
   of stellar mass black hole.

436
00:25:40,339 --> 00:25:44,275
  One of the ways that we look
  for stellar mass black holes,

437
00:25:44,277 --> 00:25:50,047
 is that they often are vampires
    eating a companion star.

438
00:25:53,786 --> 00:25:58,188
  Narrator: These vampires are
     part of a binary pair,

439
00:25:58,190 --> 00:26:02,560
    a stellar mass black hole
  in orbit with a living star,

440
00:26:02,562 --> 00:26:05,930
     the black hole feasting
         on its partner.

441
00:26:07,366 --> 00:26:08,732
Tremblay: That black hole

442
00:26:08,734 --> 00:26:11,468
   is like a very, very deadly
     parasite for that star.

443
00:26:11,470 --> 00:26:14,271
       It is ripping mass
  off the surface of that star,

444
00:26:14,273 --> 00:26:17,641
 and that matter is raining down
  toward the black hole itself.

445
00:26:20,980 --> 00:26:23,047
             Sutter:
  And that material lights up,

446
00:26:23,049 --> 00:26:25,616
        so this allows us
    to hunt for black holes,

447
00:26:25,618 --> 00:26:28,686
   not through taking pictures
    of black holes directly,

448
00:26:28,688 --> 00:26:32,990
 but through seeing the material
      falling to its doom.

449
00:26:32,992 --> 00:26:35,059
    Narrator: The problem is,

450
00:26:35,061 --> 00:26:37,394
gas and dust spread
      throughout the galaxy

451
00:26:37,396 --> 00:26:41,599
    stops visible light from
 the binary pair reaching earth.

452
00:26:41,601 --> 00:26:44,702
   But the binary pair release
      another type of light

453
00:26:44,704 --> 00:26:48,806
   that passes through the gas
     and dust more easily --

454
00:26:48,808 --> 00:26:50,741
             x-rays.

455
00:26:50,743 --> 00:26:53,277
  Mingarelli: The system itself
       is emitting x-rays,

456
00:26:53,279 --> 00:26:55,279
        so they're called
         x-ray binaries.

457
00:26:55,281 --> 00:26:57,948
      So these are useful,
   because the x-ray emission

458
00:26:57,950 --> 00:26:59,450
      can be very powerful

459
00:26:59,452 --> 00:27:02,152
   and can be potentially seen
from the earth,

460
00:27:02,154 --> 00:27:04,221
     even though the binary
        is very far away,

461
00:27:04,223 --> 00:27:06,023
  say, at the galactic center.

462
00:27:08,628 --> 00:27:12,396
 Narrator: The glowing disks of
material in x-ray binary systems

463
00:27:12,398 --> 00:27:16,000
   are almost a million times
 smaller than the accretion disk

464
00:27:16,002 --> 00:27:19,336
 surrounding sagittarius a-star,
            too small

465
00:27:19,338 --> 00:27:23,540
   for us to see the material
 swirling around them in detail.

466
00:27:25,044 --> 00:27:30,447
  So, we see the x-ray binaries
  as pinpricks of x-ray light.

467
00:27:33,185 --> 00:27:36,787
       Astronomers detect
   12 of these x-ray binaries

468
00:27:36,789 --> 00:27:40,357
in a small 3-light-year-wide
         patch of space

469
00:27:40,359 --> 00:27:42,192
     at the galactic center.

470
00:27:42,194 --> 00:27:44,762
 And that means that there could
   be a much larger collection

471
00:27:44,764 --> 00:27:47,765
of these relatively tiny stellar
        mass black holes

472
00:27:47,767 --> 00:27:51,268
   in the heart of our galaxy.

473
00:27:51,270 --> 00:27:53,671
   If black holes form the way
        we think they do,

474
00:27:53,673 --> 00:27:56,440
        there very likely
  may be swarms of black holes

475
00:27:56,442 --> 00:27:58,542
          racing around
       sagittarius a-star.

476
00:28:01,480 --> 00:28:04,448
  Narrator: But x-ray binaries
 that are powerful enough for us

477
00:28:04,450 --> 00:28:08,852
to detect are incredibly rare.

478
00:28:08,854 --> 00:28:13,590
   So we estimate that for the
dozen x-ray binaries discovered,

479
00:28:13,592 --> 00:28:15,526
        there could be up
       to a thousand more.

480
00:28:15,528 --> 00:28:20,798
                     ♪

481
00:28:20,800 --> 00:28:25,536
    in total, there could be
 20,000 stellar mass black holes

482
00:28:25,538 --> 00:28:28,672
      in this 3-light-year
        region of space.

483
00:28:28,674 --> 00:28:38,048
                     ♪

484
00:28:38,050 --> 00:28:41,852
    why are these black holes
 swarming in the galaxy center?

485
00:28:41,854 --> 00:28:45,789
   It appears they've migrated
 from the rest of the milky way.

486
00:28:47,326 --> 00:28:49,359
   Tremblay: Through a process
called dynamical friction,

487
00:28:49,361 --> 00:28:51,862
  black holes can actually sink
   to the centers of galaxies

488
00:28:51,864 --> 00:28:55,933
    very, very rapidly, like
  dropping a stone into a pond.

489
00:28:55,935 --> 00:28:58,101
         What that means
       is that an errant,

490
00:28:58,103 --> 00:29:00,003
      wandering black hole
        might eventually

491
00:29:00,005 --> 00:29:02,606
 find its way toward the center
       of our own galaxy,

492
00:29:02,608 --> 00:29:06,577
    where sagittarius a-star
            resides.

493
00:29:06,579 --> 00:29:10,614
 Narrator: As stellar mass black
     holes orbit the galaxy,

494
00:29:10,616 --> 00:29:12,683
  they interact gravitationally

495
00:29:12,685 --> 00:29:15,586
with stars and clouds
        of gas and dust.

496
00:29:17,389 --> 00:29:20,524
       These interactions
      push the black holes

497
00:29:20,526 --> 00:29:23,827
       towards the center
         of the galaxy,

498
00:29:23,829 --> 00:29:25,429
  where the black holes swarm.

499
00:29:25,431 --> 00:29:30,367
                     ♪

500
00:29:30,369 --> 00:29:34,471
     a swarm of stellar mass
   black holes sounds deadly,

501
00:29:34,473 --> 00:29:37,007
        but it may not be
      the most lethal thing

502
00:29:37,009 --> 00:29:38,842
 in the center of the milky way.

503
00:29:41,313 --> 00:29:45,382
    A surprising observation
  indicates that there is a lot

504
00:29:45,384 --> 00:29:49,386
          of antimatter
  in the center of our galaxy.

505
00:29:49,388 --> 00:29:52,523
Narrator: And when antimatter
          meets matter,

506
00:29:52,525 --> 00:29:55,225
   the results are explosive.

507
00:29:58,898 --> 00:30:05,602
                     ♪

508
00:30:05,604 --> 00:30:07,437
       narrator: In 2017,

509
00:30:07,439 --> 00:30:11,875
   astronomers tried to solve
 a decades-old cosmic mystery...

510
00:30:14,814 --> 00:30:17,748
         ...Unexplained
      high-energy radiation

511
00:30:17,750 --> 00:30:19,683
  streaming through our galaxy.

512
00:30:23,422 --> 00:30:25,923
    At first, we didn't know
       where it was from.

513
00:30:28,427 --> 00:30:31,228
        But we discovered
     it was gamma radiation

514
00:30:31,230 --> 00:30:34,932
      coming from somewhere
 in the center of the milky way.

515
00:30:37,536 --> 00:30:40,237
        The question is,
what's making these gamma rays?

516
00:30:40,239 --> 00:30:41,972
       That's hard to do.

517
00:30:41,974 --> 00:30:43,507
          It's not like
 you can rub your hands together

518
00:30:43,509 --> 00:30:46,910
    and generate gamma rays.

519
00:30:46,912 --> 00:30:48,979
 Narrator: When we took a closer
     look at the gamma rays,

520
00:30:48,981 --> 00:30:52,783
   we discovered the signature
 of the most explosive substance

521
00:30:52,785 --> 00:30:55,419
 in the universe -- antimatter.

522
00:30:59,258 --> 00:31:02,559
       Antimatter is like
          normal matter

523
00:31:02,561 --> 00:31:04,561
    but with opposite charge.

524
00:31:04,563 --> 00:31:07,030
           That's it.
    It's matter's evil twin.

525
00:31:09,134 --> 00:31:11,935
            Narrator:
When evil twin meets good twin,

526
00:31:11,937 --> 00:31:14,404
   it is not a happy reunion.

527
00:31:17,309 --> 00:31:18,742
   Plait: Antimatter is scary.

528
00:31:18,744 --> 00:31:21,445
     It's not like you want
  to have some in your kitchen.

529
00:31:21,447 --> 00:31:23,647
       This stuff is very,
         very explosive,

530
00:31:23,649 --> 00:31:25,749
      if you want to think
         of it that way.

531
00:31:25,751 --> 00:31:27,484
  If it touches normal matter,

532
00:31:27,486 --> 00:31:29,786
       it releases a huge
        amount of energy.

533
00:31:31,724 --> 00:31:33,757
      Narrator: When matter
     and antimatter combine,

534
00:31:33,759 --> 00:31:36,159
   they annihilate each other
          and transform

535
00:31:36,161 --> 00:31:39,663
into high-energy radiation,
    just like the gamma rays

536
00:31:39,665 --> 00:31:42,766
       seen streaming out
 of the center of the milky way.

537
00:31:44,603 --> 00:31:47,537
        We see antimatter
     throughout the galaxy,

538
00:31:47,539 --> 00:31:49,973
         but strangely,
       the galactic center

539
00:31:49,975 --> 00:31:54,511
     seemed to have 40% more
 antimatter than anywhere else.

540
00:31:56,815 --> 00:31:58,649
     Right now in the heart
         of our galaxy,

541
00:31:58,651 --> 00:32:01,685
       we actually observe
     fountains of antimatter

542
00:32:01,687 --> 00:32:04,655
       that are producing
        10 trillion tons

543
00:32:04,657 --> 00:32:07,824
          of antimatter
every second.

544
00:32:07,826 --> 00:32:09,526
    One of the big questions
    that we've wondered about

545
00:32:09,528 --> 00:32:12,429
 for a very long time, is what's
    the origin of this stuff?

546
00:32:15,801 --> 00:32:19,403
      Narrator: Initially,
  there were several suspects.

547
00:32:19,405 --> 00:32:21,171
   Plait: One possible source
          of antimatter

548
00:32:21,173 --> 00:32:24,808
   is the central black hole,
       sagittarius a-star.

549
00:32:24,810 --> 00:32:26,443
     Matter can be swirling
           around this

550
00:32:26,445 --> 00:32:28,178
         and it can have
        such high energy

551
00:32:28,180 --> 00:32:29,947
 that it can create antimatter.

552
00:32:33,218 --> 00:32:34,918
  Narrator: But the antimatter

553
00:32:34,920 --> 00:32:37,054
isn't coming
      from a single point,

554
00:32:37,056 --> 00:32:41,558
  it's spread across thousands
    of light-years of space.

555
00:32:41,560 --> 00:32:43,226
      So sagittarius a-star

556
00:32:43,228 --> 00:32:46,730
       can't be the source
    of the gamma-ray stream.

557
00:32:49,668 --> 00:32:52,569
         Another suspect
        was dark matter.

558
00:32:55,040 --> 00:32:56,573
  One of the biggest mysteries
         in the universe

559
00:32:56,575 --> 00:32:58,642
    right now is dark matter.

560
00:32:58,644 --> 00:33:01,511
    We know that the majority
     of mass in the universe

561
00:33:01,513 --> 00:33:03,146
     is not in the same form
          that we are.

562
00:33:03,148 --> 00:33:04,915
     It's not made of atoms,

563
00:33:04,917 --> 00:33:07,451
but whatever sort of particle
        it is or may be,

564
00:33:07,453 --> 00:33:10,854
    if these things collide,
  they can produce antimatter,

565
00:33:10,856 --> 00:33:12,589
      and that will produce
         the gamma rays.

566
00:33:12,591 --> 00:33:15,225
So it's possible that as we look
  into the heart of the galaxy

567
00:33:15,227 --> 00:33:17,027
 and see these extra gamma rays,

568
00:33:17,029 --> 00:33:19,629
        that's the signal
   that dark matter is there.

569
00:33:23,669 --> 00:33:26,737
   Narrator: But the gamma ray
 stream we detected is too weak

570
00:33:26,739 --> 00:33:29,139
      to have been created
         by dark matter.

571
00:33:31,810 --> 00:33:35,679
   Then we had a breakthrough.

572
00:33:35,681 --> 00:33:40,317
We discovered that a special
    metal called titanium-44

573
00:33:40,319 --> 00:33:43,487
      could be responsible
    for the gamma-ray stream.

574
00:33:47,326 --> 00:33:50,527
     Titanium-44 is a highly
      radioactive element.

575
00:33:50,529 --> 00:33:52,229
         That means that
        it wants to decay

576
00:33:52,231 --> 00:33:54,064
   into other types of nuclei.

577
00:33:57,069 --> 00:33:59,636
            Narrator:
    When titanium-44 decays,

578
00:33:59,638 --> 00:34:01,438
    it gives off antimatter.

579
00:34:01,440 --> 00:34:05,675
  But to produce the antimatter
   seen in the galaxy's core,

580
00:34:05,677 --> 00:34:09,112
         you would need
      a lot of titanium-44.

581
00:34:09,114 --> 00:34:14,217
       It could be created
in rare energetic events,

582
00:34:14,219 --> 00:34:18,655
  in the collision of two dead
     stars -- white dwarfs.

583
00:34:20,559 --> 00:34:23,393
  A white dwarf star is a star
  that didn't have enough mass

584
00:34:23,395 --> 00:34:25,996
          when it died
 to actually become a supernova.

585
00:34:25,998 --> 00:34:28,665
    It just sort of cools off
    as a dead little cinder.

586
00:34:28,667 --> 00:34:30,333
      But what if you have
        two white dwarfs

587
00:34:30,335 --> 00:34:32,135
        that are orbiting
       around each other,

588
00:34:32,137 --> 00:34:34,938
     and as they come closer
     and closer and collide,

589
00:34:34,940 --> 00:34:36,907
      all of a sudden now,
      you have enough mass

590
00:34:36,909 --> 00:34:39,276
to actually kick
   a supernova explosion off.

591
00:34:39,278 --> 00:34:44,347
                     ♪

592
00:34:44,349 --> 00:34:46,183
     these particular kinds
          of supernovae

593
00:34:46,185 --> 00:34:49,052
          are very good
    at producing titanium-44.

594
00:34:50,856 --> 00:34:53,657
  So these kinds of supernovas
       are very, very good

595
00:34:53,659 --> 00:34:55,292
      at making antimatter.

596
00:34:57,863 --> 00:35:00,864
   Narrator: These supernovas
 erupt in the core of the galaxy

597
00:35:00,866 --> 00:35:03,200
     once every 2,000 years.

598
00:35:06,205 --> 00:35:09,139
     But outside of the core
    in the disk of the galaxy

599
00:35:09,141 --> 00:35:11,374
where our solar system orbits...

600
00:35:13,512 --> 00:35:16,746
...These supernovas happen
      three times as often.

601
00:35:18,317 --> 00:35:22,152
  So the gamma ray observations
           were wrong.

602
00:35:22,154 --> 00:35:25,856
   There isn't more antimatter
   in the heart of the galaxy.

603
00:35:25,858 --> 00:35:28,091
  It's our region of the galaxy

604
00:35:28,093 --> 00:35:31,194
          that contains
      the most antimatter.

605
00:35:33,365 --> 00:35:36,133
 Question is, are we in danger?

606
00:35:38,570 --> 00:35:39,769
             Plait:
 If you take an ounce of matter

607
00:35:39,771 --> 00:35:41,738
   and an ounce of antimatter
        and collide them,

608
00:35:41,740 --> 00:35:45,175
        you're generating
      a megaton of energy,

609
00:35:45,177 --> 00:35:49,779
the equivalent of a million tons
        of tnt exploding.

610
00:35:49,781 --> 00:35:51,748
        So you don't need
   much antimatter to generate

611
00:35:51,750 --> 00:35:54,684
    a vast amount of energy.

612
00:35:54,686 --> 00:35:56,887
     But the thing you have
     to remember is we live

613
00:35:56,889 --> 00:35:59,156
       in this wonderful,
      dramatic environment

614
00:35:59,158 --> 00:36:00,357
      of a larger universe.

615
00:36:00,359 --> 00:36:01,725
       It's not dangerous.

616
00:36:01,727 --> 00:36:04,761
   It's very far away from us,
      and it's fascinating.

617
00:36:07,232 --> 00:36:10,567
   But all of this antimatter
is being produced in our galaxy,

618
00:36:10,569 --> 00:36:13,603
        so just sit back
and enjoy the fireworks.

619
00:36:15,874 --> 00:36:18,375
      Narrator: The center
        of the milky way

620
00:36:18,377 --> 00:36:19,876
     is violent and extreme,

621
00:36:19,878 --> 00:36:22,812
      but things could get
       a whole lot worse.

622
00:36:24,683 --> 00:36:26,850
 Rogue supermassive black holes

623
00:36:26,852 --> 00:36:30,053
            could be
    lurking near our galaxy,

624
00:36:30,055 --> 00:36:34,024
     and they have the power
   to end life as we know it.

625
00:36:38,564 --> 00:36:45,202
                     ♪

626
00:36:45,204 --> 00:36:49,439
            narrator:
     The milky way is around
   100,000 light-years across,

627
00:36:49,441 --> 00:36:54,511
    and it's home to at least
       200 billion stars,

628
00:36:54,513 --> 00:36:58,048
but it hasn't
     always been this large.

629
00:36:58,050 --> 00:37:01,418
   We know that our milky way
     galaxy grew to the size

630
00:37:01,420 --> 00:37:06,756
    it is now, which is huge,
    by eating other galaxies.

631
00:37:06,758 --> 00:37:09,059
   And some of these galaxies
          would've had

632
00:37:09,061 --> 00:37:11,561
    supermassive black holes
        in their centers.

633
00:37:14,199 --> 00:37:16,866
            Narrator:
  When the milky way's gravity

634
00:37:16,868 --> 00:37:18,668
   pulled in smaller galaxies,

635
00:37:18,670 --> 00:37:23,807
     most of their material
   merged with the milky way,

636
00:37:23,809 --> 00:37:25,976
  but some material like stars,

637
00:37:25,978 --> 00:37:29,446
could've been slung tens
   of thousands of light-years

638
00:37:29,448 --> 00:37:31,081
      out of the milky way.

639
00:37:33,385 --> 00:37:36,886
     This could've happened
      to a smaller galaxy's

640
00:37:36,888 --> 00:37:39,789
    super massive black hole.

641
00:37:39,791 --> 00:37:41,458
 Plait: It is entirely possible

642
00:37:41,460 --> 00:37:43,526
     there are supermassive
           black holes

643
00:37:43,528 --> 00:37:46,963
   wandering around out there,
       not in the center.

644
00:37:49,401 --> 00:37:51,201
   Thaller: So how could it be
 possible that there's actually

645
00:37:51,203 --> 00:37:53,970
    a supermassive black hole
  close to us wandering around,

646
00:37:53,972 --> 00:37:55,739
    but we never even see it?

647
00:37:55,741 --> 00:37:59,209
Well, remember black hole
means it's really, really black.

648
00:37:59,211 --> 00:38:02,045
  It actually absorbs radiation
         and any energy.

649
00:38:02,047 --> 00:38:04,481
 So unless something is falling
        into a black hole

650
00:38:04,483 --> 00:38:08,385
     or orbiting around it,
   you're not going to see it.

651
00:38:08,387 --> 00:38:09,953
    Tremblay: And so, if this
     supermassive black hole

652
00:38:09,955 --> 00:38:13,256
  were hypothetically wandering
  the outskirts of our galaxy,

653
00:38:13,258 --> 00:38:15,225
    well, there's a lot less
            gas there

654
00:38:15,227 --> 00:38:16,926
for that black hole to run into.

655
00:38:16,928 --> 00:38:18,128
  And if there's no gas around

656
00:38:18,130 --> 00:38:20,530
that black hole,
       we will not see it.

657
00:38:22,668 --> 00:38:26,102
Narrator: The rogue supermassive
     black hole may not stay

658
00:38:26,104 --> 00:38:29,005
        in the outskirts
     of the galaxy forever.

659
00:38:29,007 --> 00:38:32,642
   Gravitational interactions
       slowly pull it back

660
00:38:32,644 --> 00:38:34,644
       into the milky way.

661
00:38:34,646 --> 00:38:36,446
    Billions of years later,

662
00:38:36,448 --> 00:38:41,217
   the supermassive black hole
   could arrive in the center.

663
00:38:45,557 --> 00:38:48,692
  When this rogue supermassive
    black hole meets up with

664
00:38:48,694 --> 00:38:53,530
       sagittarius a-star,
        the fuse is lit.

665
00:38:55,167 --> 00:38:57,634
         The pair spiral
towards each other...

666
00:39:00,906 --> 00:39:02,872
 ...Spinning faster and faster,

667
00:39:02,874 --> 00:39:05,442
       reaching up to half
       the speed of light.

668
00:39:05,444 --> 00:39:10,680
                     ♪

669
00:39:10,682 --> 00:39:14,517
            finally,
   the two black holes merge.

670
00:39:14,519 --> 00:39:20,790
                     ♪

671
00:39:20,792 --> 00:39:21,991
    tremblay: You would have

672
00:39:21,993 --> 00:39:24,160
  an enormously energetic event
         on your hands.

673
00:39:24,162 --> 00:39:26,663
 Those supermassive black holes
      could, in principle,

674
00:39:26,665 --> 00:39:30,533
  merge together, create a huge
  blast of gravitational waves,

675
00:39:30,535 --> 00:39:34,371
   accompanied by a profoundly
    energetic flash of light

676
00:39:34,373 --> 00:39:37,040
that could, in principle,
   endanger all life on earth.

677
00:39:37,042 --> 00:39:43,146
                     ♪

678
00:39:43,148 --> 00:39:45,648
             plait:
   It's literally a stretching

679
00:39:45,650 --> 00:39:47,817
and contracting of space itself.

680
00:39:47,819 --> 00:39:50,053
       It's like grabbing
     the framework of space

681
00:39:50,055 --> 00:39:51,921
and it's shaking it really hard.

682
00:39:51,923 --> 00:39:53,890
       And if this happens
         in our galaxy,

683
00:39:53,892 --> 00:39:59,028
  the amount of energy emitted,
       that would be bad.

684
00:40:01,099 --> 00:40:03,299
            Narrator:
  When the black holes collide,

685
00:40:03,301 --> 00:40:04,634
    they release more energy

686
00:40:04,636 --> 00:40:08,671
       than all the stars
in the galaxy combined.

687
00:40:08,673 --> 00:40:15,478
                     ♪

688
00:40:15,480 --> 00:40:17,847
  plait: Should we be panicked
           about this?

689
00:40:17,849 --> 00:40:19,249
      And the answer is no.

690
00:40:19,251 --> 00:40:21,184
   The earth has been orbiting
             the sun

691
00:40:21,186 --> 00:40:23,887
     for 4 1/2 billion years
  without any incident, right?

692
00:40:23,889 --> 00:40:26,523
  We're pretty safe from them.

693
00:40:26,525 --> 00:40:30,660
 Narrator: If we were around to
see the two black holes collide,

694
00:40:30,662 --> 00:40:33,396
      we'd witness the most
     destructive light show

695
00:40:33,398 --> 00:40:35,331
  in the history of the galaxy.

696
00:40:38,003 --> 00:40:43,339
 But for now, the center of our
galaxy is relatively quiet,

697
00:40:43,341 --> 00:40:46,376
         but it's still
     a terrible place to be.

698
00:40:49,915 --> 00:40:53,049
   The center of our milky way
    is not a friendly place.

699
00:40:53,051 --> 00:40:56,820
  It's nowhere you want to be.
    It's a bad neighborhood.

700
00:40:56,822 --> 00:41:00,924
    You've got tons of stars,
       tons of radiation,

701
00:41:00,926 --> 00:41:05,028
    and stars are being born
    and dying and exploding.

702
00:41:05,030 --> 00:41:06,896
     You've got the central
    supermassive black hole.

703
00:41:06,898 --> 00:41:09,566
  You've got a potential swarm
         of black holes.

704
00:41:09,568 --> 00:41:12,001
   You've got accretion disks.
You've got flares.

705
00:41:12,003 --> 00:41:16,105
 You've got magnetic outbursts.
        You've got jets.

706
00:41:16,107 --> 00:41:18,675
    Let's just stay out here
   in the suburbs, all right?

707
00:41:20,812 --> 00:41:22,145
            Narrator:
    The center of our galaxy

708
00:41:22,147 --> 00:41:25,815
 is one of the most nightmarish
      places in the cosmos.

709
00:41:28,620 --> 00:41:32,021
     It's also home to some
  of the most incredible forces

710
00:41:32,023 --> 00:41:33,723
   the universe has to offer.

711
00:41:36,528 --> 00:41:39,195
       Whatever the future
     holds for our galaxy...

712
00:41:41,600 --> 00:41:46,870
  ...The core of the milky way
will be at the center of it all.

713
00:41:46,872 --> 00:41:50,406
Our home galaxy, the milky way,
       is our safe harbor,

714
00:41:50,408 --> 00:41:53,776
    our island in this vast,
          cosmic ocean.

715
00:41:53,778 --> 00:41:56,779
      And so to understand
    the heart of our galaxy,

716
00:41:56,781 --> 00:42:00,517
    is to understand our home
      in this cosmic void.