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Narrator:
Our milky way is under threat.
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00:00:04,839 --> 00:00:08,774
Across the universe,
galaxies are going dark,
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00:00:08,776 --> 00:00:12,478
And scientists
are trying to find out why.
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Something is slowly drawing the
curtains closed on the universe.
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Narrator: Why are the stars in
our galaxy losing their shine?
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Will the milky way
slowly fade to black?
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If our home galaxy
is getting dimmer,
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What does it mean for us?
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Narrator: Astronomers are now
racing to unlock the mystery
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Of why galaxies are darkening.
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Is there a link to massive
bubbles of dust and gas,
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That shoot out from the center
of the milky way?
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We have discovered something
truly extraordinary.
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Can the biggest collisions
in the universe
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Switch the lights back on?
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Oluseyi:
We thought galaxy collisions
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Would be very violent
and destructive,
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But what we find is that
they're one of
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The most creative processes
in the universe.
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Narrator: Scientists
are gathering evidence
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For a startling theory...
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Of how galaxies are born...
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Live...
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And die.
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-- Captions by vitac --
www.Vitac.Com
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Captions paid for by
discovery communications
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♪♪
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Our galaxy, the milky way,
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Is just one of many
hundreds of billions of galaxies
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In the universe.
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Galaxies are huge,
glowing concentrations
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Of gas, dust, stars,
and planets.
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Telescopes capture
breathtaking pictures
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Of bright, shining galaxies
millions of light years away.
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Thaller: There are few things
that make my jaw drop
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Like images of galaxies --
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When you think about how vast
they are and just how beautiful
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And also just how recent it is
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That we understand
what these things really are.
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The basic component that we see
of galaxies are stars,
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And that's what keeps
these galaxies shining.
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The milky way is
an enormous disc galaxy,
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About 120,000 light years
across,
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And it has several
hundred billion stars in it.
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Narrator: In 2015, astronomers
make a worrying discovery.
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They report that something
strange is happening
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Across the universe.
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Hundreds of thousands of
galaxies are getting dimmer.
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Some have lost 50 percent
of their brightness
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Over the past two billion years,
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And the milky way
is one of them.
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Tremblay: This isn't just
happening somewhere
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In the deep void of space
in an unknown galaxy.
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This is our home galaxy,
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And anything that affects
our home galaxy affects us.
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Narrator:
The way the galaxies recycle
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Their precious star-building
material
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Should keep them
shining brightly.
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As some stars reach the end
of their lives,
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They go supernova.
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This giant explosion
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Catapults a huge wave of gas
across the galaxy.
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This wave injects new material
into interstellar gas clouds
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And compresses them to the point
where gravity takes hold.
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Gravity pulls the material
tighter together
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And triggers the formation
of a new generation of stars.
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Over time, this process
keeps the milky way bright
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As billions of stars
burst into life.
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♪♪
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Thaller: To me, one of the most
beautiful stories ever told
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Is the cycle of star formation.
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So in a galaxy, you have these
giant clouds of dust and gas
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That collapse
into massive stars.
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Those stars then live
their lives and blow up
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And distribute their material
back into the galaxy
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For new stars and new planets
to be made of.
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So that cycle of star formation
is what keeps galaxies bright.
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♪♪
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Narrator: But it appears that
something is going wrong
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With this galactic circle
of life across the universe.
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The shocking thing is that our
own galaxy could be in decline,
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So the lights could go out
in our night sky.
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Galaxies are huge systems of gas
and dust and stars.
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So whatever's turning them off
must be something major.
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Narrator: Why are galaxies
losing their shine?
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And what does this process,
called galactic dimming,
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Mean for our own milky way?
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Astronomers believe that
the heart of our own galaxy
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Is a good place
to search for answers.
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The center of the milky way
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Contains the greatest
concentration of stars.
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Focusing on this area
gives scientists
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Studying galactic
dimming a huge sample size
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Compared to smaller clusters
of stars
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On the edges of the galaxy.
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Thaller: If you want to study
the history
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Of star formation
in the milky way,
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Why not look towards
where there are most stars?
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And that's the center
of the galaxy.
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Narrator: But astronomers face
a big problem --
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Seeing clearly this far
into space from earth.
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Thick clouds of dust and gas
lie between us
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And the center of the galaxy.
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These clouds block the visible
light that our eyes see.
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Infrared light passes
through this dense gas.
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Astronomers use special infrared
detectors to study objects
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That other types of telescopes
cannot see.
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But the water molecules
in earth's atmosphere
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Absorb almost all
of the infrared light
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Before it reaches
the planet's surface.
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This reduces the level of detail
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That the telescopes
on the ground see,
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Even telescopes on mountaintops
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Higher than 16,000 feet
above sea level
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Struggle for clear view.
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To overcome the problem,
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Nasa and the german
aerospace agency build this --
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The stratospheric observatory
for infrared astronomy,
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Or sofia for short.
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Sofia is a modified boeing 747
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That flies in the stratosphere
above the clouds
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And carries a high-powered
telescope.
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With its eight-foot mirror
and infrared sensor,
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The telescope sees
past galactic gas and dust
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To detect objects
far out in space.
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Sofia looks through a corridor
650 light years wide,
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Right into the super
bright center of the milky way.
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This has the most star-forming
matter in the galaxy,
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So sofia's infrared sensors
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Can count the number
of newly born stars.
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The data from sofia,
combined with the data
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From space telescopes
in orbit around the earth,
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Builds up a super detailed image
of the center of the milky way,
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Sofia's observations confirm
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That the galactic center
contains the largest
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And densest concentrations
of gas in the galaxy,
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These dense gas concentrations
should collapse
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To make new stars.
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The more gas that collapses,
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The more stars
that a galaxy creates.
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But the telescope data shows
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That this isn't what is
happening in the milky way.
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Thaller: As we look into
the center of the galaxy,
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We see these dense, dark regions
that should be forming stars.
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But for some reason,
they're not.
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Something is damping
down star formation
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In the heart of the milky way.
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Narrator:
The gasses left over from the
death of one generation of stars
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Should help give birth
to the next generation.
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But sofia discovers that many
of the giant gas clouds
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In the center of the milky way
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Are not collapsing
into new stars.
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Astronomers find that these
gas clouds are giving birth
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To ten times
fewer stars than expected.
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Tremblay:
Though there are some regions
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That are very dense with gas
and forming stars very actively,
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Some places in our galaxy
still host gas,
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And yet they're not
forming stars at all.
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Without the light
from these new stars,
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The galaxy
is losing its brightness.
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Oluseyi:
Stars are temporary things.
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They're born, and they die,
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So in order for a galaxy
to stay the same brightness,
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You need to have
a relative equilibrium
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With the number of stars
being born
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And a number of stars
dying equaling
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So that the lights
don't really change.
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And we had an image
of the milky way
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From a few billion years ago,
what we notice
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Is that the cumulative
amount of starlight has dropped.
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Narrator:
The evidence is clear.
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The milky way produces
fewer stars
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Now than it did in the past,
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And that is why it is dimming.
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Fewer new stars means
that our galaxy is slowly dying.
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What is putting the brakes
on star formation in galaxies
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Like the milky way?
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Are mysterious
galactic bubbles,
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00:10:01,835 --> 00:10:05,036
The key to solving
what is killing our galaxy.
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Narrator: Galaxies across
the universe are getting dimmer.
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Telescope observations
reveal that something
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Is preventing the formation
of new stars in the milky way.
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Thaller: Star formation
is a powerful process.
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The scales are unbelievable,
and yet all over the galaxy,
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Things seem to be shutting down.
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Did something happen
in the past --
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Something huge, some cataclysm
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That actually shut off
star formation?
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And can we find
any evidence of this?
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Narrator: That evidence
could lie in data
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From nasa's fermi telescope.
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00:10:50,550 --> 00:10:55,887
Fermi scans space for super high
energy light called gamma rays.
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Tremblay: The gamma ray sky
is a completely different view
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00:10:58,625 --> 00:11:00,191
Of the universe.
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The fermi telescope
is able to witness
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00:11:02,062 --> 00:11:06,031
The most energetic events that
are happening throughout it.
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00:11:06,033 --> 00:11:10,835
Narrator:
The telescope discovers
something incredible...
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00:11:10,837 --> 00:11:13,872
Two super huge bubbles
of gamma radiation
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00:11:13,874 --> 00:11:18,610
Emanating from the center
of our galaxy.
200
00:11:18,612 --> 00:11:22,213
The bubbles extend
25,000 light years above
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00:11:22,215 --> 00:11:26,351
And below the spiral
of the milky way.
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00:11:26,353 --> 00:11:29,554
Plait: The scale of these
fermi bubbles is enormous.
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00:11:29,556 --> 00:11:31,756
They're roughly the radius
of the galaxy --
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00:11:31,758 --> 00:11:33,992
Half the width of the galaxy.
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00:11:33,994 --> 00:11:36,428
If you were to go outside
and look up in the sky,
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00:11:36,430 --> 00:11:39,831
They would cover 2/3
of the size of the sky.
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00:11:42,769 --> 00:11:45,537
Narrator: Only the most violent
events in the universe
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00:11:45,539 --> 00:11:49,140
Have the power
to produce gamma rays...
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00:11:49,142 --> 00:11:52,177
Like supernova explosions...
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00:11:52,179 --> 00:11:54,245
And neutron star quakes.
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00:11:56,616 --> 00:11:57,916
Neither is powerful enough
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00:11:57,918 --> 00:12:00,218
To unleash
the amount of gamma radiation
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00:12:00,220 --> 00:12:03,722
That turns into
the fermi bubbles.
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00:12:03,724 --> 00:12:05,657
So what made them?
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00:12:08,161 --> 00:12:10,562
Scientists think
an invisible monster
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00:12:10,564 --> 00:12:13,698
At the center of the milky way
could be responsible.
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00:12:16,002 --> 00:12:17,769
At the heart of every galaxy
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00:12:17,771 --> 00:12:21,639
Lurks a supermassive
black hole...
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00:12:21,641 --> 00:12:25,543
A point in space so dense that
nothing can escape its gravity.
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00:12:27,681 --> 00:12:29,380
Oluseyi:
From what we've observed,
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00:12:29,382 --> 00:12:32,751
Every galaxy has a supermassive
black hole at its core,
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00:12:32,753 --> 00:12:35,820
And there are at least
two trillion galaxies
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00:12:35,822 --> 00:12:37,922
In the observable universe,
so this means
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00:12:37,924 --> 00:12:42,660
There are trillions
of supermassive black holes.
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00:12:42,662 --> 00:12:45,730
Narrator:
The supermassive black hole
at the center of the milky way
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00:12:45,732 --> 00:12:49,667
Is called sagittarius a-star.
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00:12:49,669 --> 00:12:54,105
It weighs the equivalent
of four million suns.
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00:12:54,107 --> 00:12:56,307
This black hole's
enormous gravity
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00:12:56,309 --> 00:12:58,977
Draws in anything
that gets too close.
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00:13:01,848 --> 00:13:05,784
The energy unleashed when this
gravity rips apart stray stars
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00:13:05,786 --> 00:13:11,556
Could unlock the mystery of
what makes the fermi bubbles.
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Black holes don't eat like
a nice, distinguished,
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00:13:15,028 --> 00:13:16,628
Gentrified person.
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00:13:16,630 --> 00:13:18,997
You know, they're sloppy.
They're like the cookie monster.
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00:13:18,999 --> 00:13:20,265
When the cookie monster
eats cookies,
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00:13:20,267 --> 00:13:22,233
More comes out
than goes into his mouth.
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Well, supermassive black holes
are just like that.
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00:13:25,071 --> 00:13:28,807
Stuff is moving incredibly fast,
approaching the speed of light,
239
00:13:28,809 --> 00:13:31,276
And the density and pressures
are incredible.
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00:13:31,278 --> 00:13:34,913
And so it's almost as if
there are explosions
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00:13:34,915 --> 00:13:37,081
In this traffic jam of material
242
00:13:37,083 --> 00:13:38,850
Trying to get
into the black hole.
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00:13:38,852 --> 00:13:41,653
And so a lot of material
gets shot out
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00:13:41,655 --> 00:13:45,390
Away from the black hole
rather than ending up inside it.
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00:13:45,392 --> 00:13:49,627
Narrator:
The more massive the objects
that the black hole consumes,
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00:13:49,629 --> 00:13:51,362
The higher the densities
and pressures
247
00:13:51,364 --> 00:13:54,065
Around the black hole become.
248
00:13:54,067 --> 00:13:55,667
And the greater
the amount of energy
249
00:13:55,669 --> 00:13:59,370
That blasts into space
as gamma radiation.
250
00:14:02,209 --> 00:14:06,477
Scientists rewind the
milky way's galactic clock.
251
00:14:06,479 --> 00:14:09,848
They predict when
sagittarius a-star feasts
252
00:14:09,850 --> 00:14:13,051
On a meal large enough
to forge the fermi bubbles.
253
00:14:15,488 --> 00:14:19,090
Some scientists estimate that
around three million years ago,
254
00:14:19,092 --> 00:14:24,162
Sagittarius a-star draws
in a vast amount of matter.
255
00:14:24,164 --> 00:14:30,268
That flattens out into
a huge, glowing, spinning disk.
256
00:14:30,270 --> 00:14:34,272
As the black hole
devours this matter.
257
00:14:34,274 --> 00:14:38,042
Two immense jets of energy
blast out from its poles.
258
00:14:40,881 --> 00:14:43,648
These jets blast gas
out of the galaxy
259
00:14:43,650 --> 00:14:46,751
25,000 light years into space.
260
00:14:48,889 --> 00:14:53,157
The jets turn off when the
black hole finishes its feast.
261
00:14:53,159 --> 00:14:56,995
All that remains are
the fermi bubbles we see today.
262
00:15:01,401 --> 00:15:04,035
Scientists think that multiple
events like this one
263
00:15:04,037 --> 00:15:06,037
Throughout the history
of the milky way
264
00:15:06,039 --> 00:15:09,574
Could unlock the mystery
of, "why are galaxies dimming?"
265
00:15:12,045 --> 00:15:15,713
The reason lies in the huge
amount of heat they unleash.
266
00:15:18,652 --> 00:15:22,553
Stars form when huge quantities
of gas and dust collapse
267
00:15:22,555 --> 00:15:24,722
Under gravity.
268
00:15:24,724 --> 00:15:27,425
The process triggers
a nuclear reaction.
269
00:15:31,564 --> 00:15:33,564
Scientists calculate
that this reaction
270
00:15:33,566 --> 00:15:36,100
Happens only
when the gas is cold.
271
00:15:38,171 --> 00:15:39,604
Plait:
Star formation is a battle
272
00:15:39,606 --> 00:15:41,606
Between these two forces
of gravity,
273
00:15:41,608 --> 00:15:43,708
Which is trying to collapse
the cloud,
274
00:15:43,710 --> 00:15:46,577
And its own internal heat,
which is trying to inflate it.
275
00:15:46,579 --> 00:15:50,081
For gravity to win,
for stars to get made,
276
00:15:50,083 --> 00:15:53,084
The gas has to be cool enough
that it doesn't stay inflated,
277
00:15:53,086 --> 00:15:55,153
That it's able to collapse.
278
00:15:57,724 --> 00:16:00,792
Narrator: The jets that
sagittarius a-star releases
279
00:16:00,794 --> 00:16:03,494
Hurl some of the richest
star-building material
280
00:16:03,496 --> 00:16:07,031
Into intergalactic space.
281
00:16:07,033 --> 00:16:11,836
This superheats the gas
at the center of the milky way.
282
00:16:11,838 --> 00:16:17,008
The clouds of gas become
too hot to collapse into stars.
283
00:16:17,010 --> 00:16:20,578
Oluseyi: All of this heat
and power and light and force
284
00:16:20,580 --> 00:16:22,780
Would have stripped out
all this material
285
00:16:22,782 --> 00:16:24,449
From the center of the galaxy.
286
00:16:24,451 --> 00:16:28,353
So it just would not have been
available to form new stars.
287
00:16:28,355 --> 00:16:30,455
Narrator:
A series of events like these
288
00:16:30,457 --> 00:16:33,224
Happening at different times
in our galaxy's history
289
00:16:33,226 --> 00:16:34,993
Could put the brakes
on star formation
290
00:16:34,995 --> 00:16:37,295
At the heart of the milky way.
291
00:16:41,534 --> 00:16:43,468
Telescopes look millions
of light years
292
00:16:43,470 --> 00:16:47,171
Through space at other galaxies.
293
00:16:47,173 --> 00:16:50,441
They discover that the damage
sagittarius a-star wreaks
294
00:16:50,443 --> 00:16:52,777
On the milky way
throughout its past
295
00:16:52,779 --> 00:16:55,613
Is not unique.
296
00:16:55,615 --> 00:16:57,949
Astronomers observe
2,000 galaxies
297
00:16:57,951 --> 00:17:01,352
That show evidence of huge blast
of gamma radiation
298
00:17:01,354 --> 00:17:05,189
Coming from the black holes
at their centers.
299
00:17:05,191 --> 00:17:09,894
And the vast majority of these
galaxies are now getting dimmer.
300
00:17:09,896 --> 00:17:12,096
Tremblay: We see it in an
enormous number of galaxies
301
00:17:12,098 --> 00:17:13,398
Throughout the universe --
302
00:17:13,400 --> 00:17:16,701
Direct signatures of violent
black hole activity
303
00:17:16,703 --> 00:17:18,669
And a depressed
star formation rate.
304
00:17:18,671 --> 00:17:22,006
There's definitely
a clear connection.
305
00:17:22,008 --> 00:17:26,044
Narrator:
But do bursts of radiation
from a supermassive black hole
306
00:17:26,046 --> 00:17:29,847
Spell doom
for a galaxy indefinitely?
307
00:17:29,849 --> 00:17:33,051
And do mysterious alien stars
unlock
308
00:17:33,053 --> 00:17:36,521
How it might be possible
to reverse galactic dimming?
309
00:17:47,300 --> 00:17:50,435
Narrator: Jets that blast out
from supermassive black holes
310
00:17:50,437 --> 00:17:53,337
Kill star birth
at the center of galaxies.
311
00:17:55,508 --> 00:18:00,344
They could explain why
our milky way is dimming.
312
00:18:00,346 --> 00:18:04,148
Will the curtains close
on our galaxy forever,
313
00:18:04,150 --> 00:18:07,785
Or is there a way it can get
a new lease of life?
314
00:18:10,156 --> 00:18:13,991
Scientists believe a clue
could lie inside a space rock
315
00:18:13,993 --> 00:18:15,626
That fell to earth.
316
00:18:17,964 --> 00:18:20,765
In 1969, a meteorite lands
317
00:18:20,767 --> 00:18:24,769
Near to the small town
of murchison, australia,
318
00:18:24,771 --> 00:18:26,771
One hundred miles
north of melbourne.
319
00:18:30,343 --> 00:18:35,913
It shatters into pieces, and
locals gather over 100 kilograms
320
00:18:35,915 --> 00:18:38,916
Of the black,
smelly meteorite fragments.
321
00:18:42,222 --> 00:18:46,591
In 2019,
scientists grind down a sample
322
00:18:46,593 --> 00:18:49,160
To analyze what it is made of.
323
00:18:49,162 --> 00:18:51,295
They get a big surprise.
324
00:18:54,134 --> 00:18:57,935
They find grains of dust
from alien stars that died
325
00:18:57,937 --> 00:19:03,407
4.6 billion years ago,
before our sun was even born.
326
00:19:05,712 --> 00:19:09,213
These grains of stardust become
locked inside space rocks
327
00:19:09,215 --> 00:19:11,582
Through the stars'
never ending cycle of birth
328
00:19:11,584 --> 00:19:13,217
And rebirth.
329
00:19:15,822 --> 00:19:19,457
Billions of years ago,
an ancient star in the milky way
330
00:19:19,459 --> 00:19:21,225
Reaches the end of its life.
331
00:19:23,329 --> 00:19:27,832
Chemical reactions inside
the star makes it grow rapidly.
332
00:19:27,834 --> 00:19:32,170
It transforms into a red giant.
333
00:19:32,172 --> 00:19:36,941
The outer layers of the star
shed grains of stardust.
334
00:19:36,943 --> 00:19:39,777
These grains travel light years
through space
335
00:19:39,779 --> 00:19:42,880
And merge with the spinning disc
of gas and dust
336
00:19:42,882 --> 00:19:47,151
Surrounding newly formed stars.
337
00:19:47,153 --> 00:19:49,921
The stardust from the dead
red giant
338
00:19:49,923 --> 00:19:53,991
Combines with the material
in the disk to make asteroids.
339
00:19:57,263 --> 00:19:59,697
It is a part of just
such an asteroid
340
00:19:59,699 --> 00:20:04,168
That falls on murchison
as a meteorite in 1969.
341
00:20:08,474 --> 00:20:12,076
These grains of dead stars
might reveal if galactic dimming
342
00:20:12,078 --> 00:20:15,513
Caused by blast of gamma
radiation spells doom
343
00:20:15,515 --> 00:20:19,550
For galaxies like the milky way.
344
00:20:19,552 --> 00:20:23,888
Different types of grains
come from different dead stars.
345
00:20:23,890 --> 00:20:26,357
Adding up the unique grains
tells astronomers
346
00:20:26,359 --> 00:20:28,593
How many stars existed
in the milky way
347
00:20:28,595 --> 00:20:30,695
At certain times in the past.
348
00:20:33,099 --> 00:20:36,601
These little pieces of stardust
inside this meteorite tell us
349
00:20:36,603 --> 00:20:39,971
The story of what was happening
in our galaxy
350
00:20:39,973 --> 00:20:42,139
Before our sun even formed.
351
00:20:42,141 --> 00:20:44,642
They're little tracers.
352
00:20:44,644 --> 00:20:48,379
Narrator:
The stars that eject the grains
found in the murchison meteorite
353
00:20:48,381 --> 00:20:52,917
Lived for between two
to 2.5 billion years.
354
00:20:52,919 --> 00:20:55,786
So it is possible for scientists
to calculate
355
00:20:55,788 --> 00:20:59,557
When these
ancient stars were born.
356
00:20:59,559 --> 00:21:03,160
By knowing that these grains
came from dying stars,
357
00:21:03,162 --> 00:21:05,863
We can actually trace backwards
in time
358
00:21:05,865 --> 00:21:11,435
To when those dying stars
were actually first forming.
359
00:21:11,437 --> 00:21:13,504
Narrator: Scientists discover
that these grains
360
00:21:13,506 --> 00:21:17,675
Come from different stars
from all over the galaxy,
361
00:21:17,677 --> 00:21:21,779
But they share one thing
in common.
362
00:21:21,781 --> 00:21:26,183
They are all born
seven billion years ago.
363
00:21:26,185 --> 00:21:29,053
Calculations reveal
that the rate of star birth
364
00:21:29,055 --> 00:21:33,758
In the milky way at that time
is double the average.
365
00:21:33,760 --> 00:21:35,926
Tremblay: This was a beautiful
and exciting result.
366
00:21:35,928 --> 00:21:37,995
It showed that the milky way
experienced
367
00:21:37,997 --> 00:21:39,563
What might have been a sudden
368
00:21:39,565 --> 00:21:41,532
And unexpected burst
of star formation
369
00:21:41,534 --> 00:21:43,434
About seven billion years ago,
370
00:21:43,436 --> 00:21:45,269
And this might not
have been a localized event.
371
00:21:45,271 --> 00:21:48,239
It might have been galaxy wide.
372
00:21:48,241 --> 00:21:53,411
Narrator:
These grains show that galactic
dimming is not inevitable.
373
00:21:53,413 --> 00:21:55,212
Galaxies like the milky way
374
00:21:55,214 --> 00:21:59,817
Experience periods
of intense star building.
375
00:21:59,819 --> 00:22:03,020
These events,
counter galactic dimming.
376
00:22:03,022 --> 00:22:06,924
They make galaxies
much brighter.
377
00:22:06,926 --> 00:22:09,327
Thaller: A galaxy is such a rich
and complex thing,
378
00:22:09,329 --> 00:22:12,129
It turns out that its life cycle
is not very simple.
379
00:22:12,131 --> 00:22:15,266
They grow, they change,
they evolve,
380
00:22:15,268 --> 00:22:20,071
And in fact, their story
may not be so doomed after all.
381
00:22:20,073 --> 00:22:22,773
Narrator: What triggers these
sudden bursts of star creation
382
00:22:22,775 --> 00:22:25,009
Within galaxies
like the milky way?
383
00:22:25,011 --> 00:22:30,448
♪♪
384
00:22:30,450 --> 00:22:33,751
A clue lies in the findings
from an observatory
385
00:22:33,753 --> 00:22:35,386
In new mexico.
386
00:22:37,357 --> 00:22:42,326
This is the sloan 100-inch
telescope.
387
00:22:42,328 --> 00:22:45,529
Sloan's apogee project studies
hundreds of stars
388
00:22:45,531 --> 00:22:47,732
In the milky way simultaneously
389
00:22:47,734 --> 00:22:50,801
During a single observation
session.
390
00:22:50,803 --> 00:22:53,838
One of the most powerful things
that we can do as astronomers
391
00:22:53,840 --> 00:22:55,673
Is take a survey
of the night sky,
392
00:22:55,675 --> 00:22:59,043
Of looking at huge chunks
of the sky at the same time,
393
00:22:59,045 --> 00:23:03,681
And mapping out
all of the stars there.
394
00:23:03,683 --> 00:23:06,083
Narrator: The light from a star
reveals information
395
00:23:06,085 --> 00:23:09,253
About the chemicals it contains.
396
00:23:09,255 --> 00:23:11,455
Apogee analyzes this starlight
397
00:23:11,457 --> 00:23:16,694
To unlock the precise chemical
makeup of thousands of stars.
398
00:23:16,696 --> 00:23:19,330
So you take the light that any
particular star emits,
399
00:23:19,332 --> 00:23:22,666
You break it up into a rainbow,
and you can see the fingerprints
400
00:23:22,668 --> 00:23:25,202
Of all the different chemicals
in there, the ratios of them,
401
00:23:25,204 --> 00:23:27,938
How much there is of
one thing versus another.
402
00:23:27,940 --> 00:23:32,676
Every single chemical
has its own rainbow fingerprint.
403
00:23:32,678 --> 00:23:35,746
Narrator: The results from
sloan's apogee project reveal
404
00:23:35,748 --> 00:23:38,149
That there's something
very strange about the chemicals
405
00:23:38,151 --> 00:23:40,718
Inside some of the stars
in the milky way.
406
00:23:42,755 --> 00:23:47,291
Stars contain 98 percent
hydrogen and helium.
407
00:23:47,293 --> 00:23:51,896
And traces of other elements
like iron, magnesium, or carbon.
408
00:23:55,668 --> 00:24:00,971
Apogee analyzes the light
from over 600,000 stars
409
00:24:00,973 --> 00:24:04,241
To decode the chemical
signature of each one.
410
00:24:07,413 --> 00:24:11,015
It finds that nearly all stars
in our galaxy,
411
00:24:11,017 --> 00:24:13,317
Regardless of their size
or color,
412
00:24:13,319 --> 00:24:15,319
Share a common signature.
413
00:24:18,958 --> 00:24:24,528
But every now and again,
apogee finds a rogue star...
414
00:24:24,530 --> 00:24:27,498
With a different signature.
415
00:24:27,500 --> 00:24:31,068
How is this possible?
416
00:24:31,070 --> 00:24:33,838
Astronomers studying
these odd stars out
417
00:24:33,840 --> 00:24:36,540
Come to an astonishing
conclusion.
418
00:24:36,542 --> 00:24:38,843
Oluseyi:
Their ratios don't match
419
00:24:38,845 --> 00:24:40,878
Everything else
in the milky way.
420
00:24:40,880 --> 00:24:44,415
By identifying stars that have
a different chemical signature
421
00:24:44,417 --> 00:24:46,317
Than other stars
in the milky way,
422
00:24:46,319 --> 00:24:48,853
The implication is clear --
423
00:24:48,855 --> 00:24:54,058
These stars did not originate
in the milky way galaxy.
424
00:24:54,060 --> 00:24:57,194
Narrator: If these stars weren't
born in the milky way,
425
00:24:57,196 --> 00:25:00,498
Then where do they come from?
426
00:25:00,500 --> 00:25:04,969
And do they unlock how to
reverse galactic dimming?
427
00:25:14,881 --> 00:25:17,147
Narrator: Astronomers discover
that our milky way
428
00:25:17,149 --> 00:25:19,416
Contains mysterious alien stars
429
00:25:19,418 --> 00:25:21,652
That were not born
in our galaxy.
430
00:25:24,490 --> 00:25:27,625
So where do they come from?
431
00:25:27,627 --> 00:25:31,228
And what is their connection
to galactic dimming?
432
00:25:34,534 --> 00:25:40,137
The european space agency's
gaia telescope finds a clue.
433
00:25:40,139 --> 00:25:43,173
The telescope maps the motion
of over a billion stars
434
00:25:43,175 --> 00:25:46,043
In the milky way.
435
00:25:46,045 --> 00:25:49,980
It discovers that these
odd stars out all travel
436
00:25:49,982 --> 00:25:51,482
On different orbits to stars
437
00:25:51,484 --> 00:25:56,387
That share the typical chemical
profiles for the milky way.
438
00:25:56,389 --> 00:25:58,355
They circle the galactic center
439
00:25:58,357 --> 00:26:01,559
In the opposite direction
to other stars
440
00:26:01,561 --> 00:26:06,230
And move on elongated
oval-shaped orbits.
441
00:26:06,232 --> 00:26:11,135
The results from gaia
lead to a startling conclusion.
442
00:26:11,137 --> 00:26:16,440
These alien stars
come from a different galaxy.
443
00:26:16,442 --> 00:26:20,177
But how can a star
jump between galaxies?
444
00:26:23,983 --> 00:26:28,919
A clue lies 250 million
light years from earth.
445
00:26:28,921 --> 00:26:32,957
This is a galaxy named arp 220.
446
00:26:32,959 --> 00:26:35,960
It has one of the strangest
shapes of any known galaxy
447
00:26:35,962 --> 00:26:38,963
In the visible universe.
448
00:26:38,965 --> 00:26:42,666
Arp 220 does not look like
a regular calm, beautiful,
449
00:26:42,668 --> 00:26:45,269
Majestic spiral galaxy
like the milky way.
450
00:26:45,271 --> 00:26:50,074
It is this train wreck blob.
It's an absolute mess.
451
00:26:50,076 --> 00:26:55,446
Narrator: Why does arp 220 look
so different to other galaxies?
452
00:26:55,448 --> 00:26:59,717
The answer is arp 220
isn't a single galaxy.
453
00:27:01,921 --> 00:27:04,221
Oluseyi:
The bent shape of arp 220
454
00:27:04,223 --> 00:27:06,824
Isn't just because
of aesthetic reasons.
455
00:27:06,826 --> 00:27:09,860
It tells us something
about the galaxy's history.
456
00:27:09,862 --> 00:27:16,266
It appears to be the result of
a merger between two galaxies.
457
00:27:16,268 --> 00:27:19,470
Narrator: The merger of two
galaxies after a collision
458
00:27:19,472 --> 00:27:25,175
Explains how alien stars can
jump from one galaxy to another.
459
00:27:25,177 --> 00:27:28,712
The discovery of odd stars out
in the milky way
460
00:27:28,714 --> 00:27:30,748
Is evidence that our galaxy,
too,
461
00:27:30,750 --> 00:27:34,451
Is involved in a collision
billions of years ago.
462
00:27:34,453 --> 00:27:36,687
Now we understand
that galactic collisions
463
00:27:36,689 --> 00:27:39,923
Are responsible
for these odd stars in the sky.
464
00:27:39,925 --> 00:27:42,593
They didn't come from
the milky way galaxy.
465
00:27:42,595 --> 00:27:43,961
So it's an amazing thing
to think
466
00:27:43,963 --> 00:27:45,496
That when you look up
in the sky,
467
00:27:45,498 --> 00:27:48,432
Some of even the nearest stars
may have began their lives
468
00:27:48,434 --> 00:27:50,534
In an entirely different galaxy.
469
00:27:53,139 --> 00:27:55,739
Narrator: Astronomers believe
that these galactic mergers
470
00:27:55,741 --> 00:27:58,876
Unlock what triggers intense
periods of star birth
471
00:27:58,878 --> 00:28:01,178
In galaxies like our own.
472
00:28:03,549 --> 00:28:07,584
The clue is that merged galaxies
like arp 220
473
00:28:07,586 --> 00:28:12,589
Are some of the most brilliant
objects in the universe.
474
00:28:12,591 --> 00:28:14,158
There are some galaxies
in the universe
475
00:28:14,160 --> 00:28:16,694
That are putting
on a spectacular show.
476
00:28:16,696 --> 00:28:18,162
They're incredibly bright.
477
00:28:18,164 --> 00:28:23,233
Their name says it all -- ultra
luminous starburst galaxies.
478
00:28:23,235 --> 00:28:26,136
Narrator: The brightness
of a galaxy like arp 220
479
00:28:26,138 --> 00:28:27,971
Is a telltale sign
480
00:28:27,973 --> 00:28:32,910
That it is producing
huge numbers of new stars.
481
00:28:32,912 --> 00:28:35,713
The raw ingredients
for this starburst
482
00:28:35,715 --> 00:28:37,581
Are the vast clouds of gas
483
00:28:37,583 --> 00:28:40,417
That wrap themselves
around every galaxy.
484
00:28:44,256 --> 00:28:45,989
Oluseyi:
When two things merge together,
485
00:28:45,991 --> 00:28:48,759
There's a lot of reproduction
of stars.
486
00:28:48,761 --> 00:28:51,495
New stars are being born.
487
00:28:51,497 --> 00:28:55,432
Just like we had a baby boom,
we have a star boom.
488
00:28:57,703 --> 00:29:00,671
Narrator:
700 million years ago.
489
00:29:00,673 --> 00:29:04,842
Two enormous spiral galaxies
are on a collision course.
490
00:29:07,079 --> 00:29:10,114
Stripping away their stars
and planets
491
00:29:10,116 --> 00:29:14,618
Reveals what happens
when they collide.
492
00:29:14,620 --> 00:29:20,858
The galactic gas and dust
compress in the collision.
493
00:29:20,860 --> 00:29:25,596
This triggers the formation
of billions of stars.
494
00:29:25,598 --> 00:29:30,134
Over millions of years
and multiple collisions,
495
00:29:30,136 --> 00:29:33,437
The two galaxies merge
into a new galaxy
496
00:29:33,439 --> 00:29:35,272
That is incredibly bright --
497
00:29:35,274 --> 00:29:37,441
Arp 220.
498
00:29:40,179 --> 00:29:41,912
So a galaxy collision sounds
499
00:29:41,914 --> 00:29:43,814
Like a really violent event,
right?
500
00:29:43,816 --> 00:29:47,117
But in fact,
it can seed new life.
501
00:29:47,119 --> 00:29:49,720
Gas is the fuel from which
all stars are born.
502
00:29:49,722 --> 00:29:53,323
So when you introduce new gas
to emerging galaxy,
503
00:29:53,325 --> 00:29:55,626
You can form
a new generation of stars.
504
00:29:59,532 --> 00:30:04,735
Narrator: Observations reveal
arp 220's origin is not unique.
505
00:30:04,737 --> 00:30:07,271
Astronomers believe
up to 80 percent
506
00:30:07,273 --> 00:30:09,940
Of ultra luminous
starburst galaxies
507
00:30:09,942 --> 00:30:12,376
Are the result
of galactic collisions.
508
00:30:14,513 --> 00:30:17,714
Could a cosmic merger be
responsible for the epic periods
509
00:30:17,716 --> 00:30:22,719
Of intense star building
and the milky way's past?
510
00:30:22,721 --> 00:30:24,354
And when will the milky way's
511
00:30:24,356 --> 00:30:27,491
Next galactic mega collision
take place?
512
00:30:27,493 --> 00:30:33,964
♪♪
513
00:30:35,601 --> 00:30:40,404
♪♪
514
00:30:40,406 --> 00:30:43,240
Narrator: Scientists are
on a mission to discover
515
00:30:43,242 --> 00:30:46,710
How galaxies can reverse
the effects of galactic dimming.
516
00:30:49,582 --> 00:30:52,716
The brightest galaxies
in the universe reveal
517
00:30:52,718 --> 00:30:58,255
That the galactic collisions
breathe new life into a galaxy.
518
00:30:58,257 --> 00:31:01,892
So when was the milky way's
last major collision?
519
00:31:05,965 --> 00:31:08,498
Astronomers plot the positions
and movements
520
00:31:08,500 --> 00:31:13,136
Of both the old
and new stars in our galaxy.
521
00:31:13,138 --> 00:31:16,940
They use this data
to rewind time
522
00:31:16,942 --> 00:31:18,742
And reveal
the event that triggers
523
00:31:18,744 --> 00:31:21,311
One of the greatest-ever periods
of star building
524
00:31:21,313 --> 00:31:22,846
In the milky way.
525
00:31:25,251 --> 00:31:29,052
Around 10 billion years ago,
the milky way collides
526
00:31:29,054 --> 00:31:34,658
With a smaller, ancient galaxy
called gaia-enceladus.
527
00:31:34,660 --> 00:31:39,363
The impact compresses together
huge clouds of gas.
528
00:31:39,365 --> 00:31:43,767
This gas collapses to make
thousands of brand-new stars.
529
00:31:43,769 --> 00:31:47,671
The milky way brightens
as more and more stars form.
530
00:31:47,673 --> 00:31:50,841
The past collision of the milky
way with gaia-enceladus
531
00:31:50,843 --> 00:31:53,777
Might have introduced
an enormous new reservoir of gas
532
00:31:53,779 --> 00:31:56,480
Into our home galaxy,
and that gas could have gone
533
00:31:56,482 --> 00:31:59,783
Into forming
a new generation of stars.
534
00:31:59,785 --> 00:32:01,385
Thaller:
When you think galaxy collision,
535
00:32:01,387 --> 00:32:03,186
It sounds like
something destructive.
536
00:32:03,188 --> 00:32:05,489
But in fact, when one galaxy
collides with another,
537
00:32:05,491 --> 00:32:07,257
That's a harbinger
of the creation
538
00:32:07,259 --> 00:32:10,227
Of a brand-new generation
of stars.
539
00:32:10,229 --> 00:32:12,629
Our own sun may have formed
when a small galaxy
540
00:32:12,631 --> 00:32:15,032
Collided with the milky way
billions of years ago.
541
00:32:15,034 --> 00:32:19,536
It's an act of violent creation.
542
00:32:19,538 --> 00:32:22,439
Narrator: A mega collision
10 billion years ago
543
00:32:22,441 --> 00:32:26,243
Reversed the milky way's
galactic dimming.
544
00:32:26,245 --> 00:32:27,678
Where else has the gas needed
545
00:32:27,680 --> 00:32:30,614
To make new stars
come from since then?
546
00:32:34,620 --> 00:32:39,556
In 2020, astronomers using data
from the gaia space probe
547
00:32:39,558 --> 00:32:41,191
Uncover a clue.
548
00:32:43,495 --> 00:32:47,531
Gaia spots a cluster of a few
thousand bright young blue stars
549
00:32:47,533 --> 00:32:50,267
In an ancient outer region
of the milky way.
550
00:32:53,105 --> 00:32:55,205
These stars burst into life
551
00:32:55,207 --> 00:32:58,008
Along a stream
of fresh hydrogen gas.
552
00:33:00,946 --> 00:33:06,016
Gaia follows the gas trail
into intergalactic space
553
00:33:06,018 --> 00:33:10,620
To a cluster of stars
outside the milky way.
554
00:33:10,622 --> 00:33:13,323
Our galaxy
is not alone in space,
555
00:33:13,325 --> 00:33:18,128
The milky way is surrounded
by dozens of smaller galaxies.
556
00:33:18,130 --> 00:33:19,463
And where we have maybe
a hundred
557
00:33:19,465 --> 00:33:21,365
Or a few hundred billion stars,
558
00:33:21,367 --> 00:33:24,468
These galaxies
only have about a billion.
559
00:33:24,470 --> 00:33:26,370
It's like we're a whale
in the ocean
560
00:33:26,372 --> 00:33:29,006
Surrounded by a school
of little fish.
561
00:33:32,911 --> 00:33:35,078
Narrator:
The new star-building gas
562
00:33:35,080 --> 00:33:37,848
Comes from the largest
of these dwarf galaxies,
563
00:33:37,850 --> 00:33:41,318
Called the large
magellanic cloud.
564
00:33:41,320 --> 00:33:44,087
The huge gravity
of the larger milky way
565
00:33:44,089 --> 00:33:47,758
Continually strips gas
from the smaller dwarf galaxy.
566
00:33:50,696 --> 00:33:55,632
The new gas collides with
the outer regions of our galaxy.
567
00:33:55,634 --> 00:33:59,436
Thousands of bright, young
blue stars burst into light.
568
00:34:01,907 --> 00:34:04,174
Astronomers estimate
that the milky way
569
00:34:04,176 --> 00:34:06,043
Will completely tear apart
the cloud
570
00:34:06,045 --> 00:34:08,912
Within the next two and a half
billion years.
571
00:34:08,914 --> 00:34:16,586
♪♪
572
00:34:16,588 --> 00:34:19,790
Dwarf galaxies like the large
magellanic cloud
573
00:34:19,792 --> 00:34:23,760
Keep the milky way
topped with star-building gas.
574
00:34:23,762 --> 00:34:25,595
Oluseyi:
The milky way isn't isolated.
575
00:34:25,597 --> 00:34:26,963
It has a lot of neighbors,
576
00:34:26,965 --> 00:34:29,366
And it's stealing gas
from some of them.
577
00:34:29,368 --> 00:34:30,667
It's ripping them apart
578
00:34:30,669 --> 00:34:33,603
And incorporating that material
into itself.
579
00:34:33,605 --> 00:34:37,974
And that's the material that may
form new stars of the future.
580
00:34:37,976 --> 00:34:40,310
The milky way is literally
sucking the gas
581
00:34:40,312 --> 00:34:44,347
Off of its neighbors
to keep itself alive.
582
00:34:44,349 --> 00:34:46,416
Narrator: Astronomers think that
there is enough gas
583
00:34:46,418 --> 00:34:48,218
In these satellite galaxies
584
00:34:48,220 --> 00:34:53,290
To keep the milky way fed
for a few billion years.
585
00:34:53,292 --> 00:34:56,560
But where will the critical
supplies of gas come from
586
00:34:56,562 --> 00:35:00,564
Once these smaller galaxies
are exhausted?
587
00:35:00,566 --> 00:35:02,499
Thaller: We want to know
what's going to happen to us,
588
00:35:02,501 --> 00:35:05,001
To our star,
in the very distant future,
589
00:35:05,003 --> 00:35:06,736
And knowing the future
of the milky way
590
00:35:06,738 --> 00:35:09,873
Will help us understand what's
gonna happen to our home.
591
00:35:12,544 --> 00:35:14,911
Narrator: Astronomers scan
the cosmos to identify
592
00:35:14,913 --> 00:35:19,683
Where the milky way's
next meal will come from.
593
00:35:19,685 --> 00:35:22,419
They discover that it is
our own galaxy
594
00:35:22,421 --> 00:35:25,989
That might be next on the menu.
595
00:35:25,991 --> 00:35:28,058
The milky way has
fed off the gas
596
00:35:28,060 --> 00:35:33,563
From around 50 smaller satellite
galaxies for billions of years,
597
00:35:33,565 --> 00:35:36,266
But it might be about
to meet its match.
598
00:35:38,871 --> 00:35:42,439
Nearby on a cosmic scale
is andromeda
599
00:35:42,441 --> 00:35:45,442
And its satellite galaxies.
600
00:35:45,444 --> 00:35:48,612
Andromeda has over
800 billion stars,
601
00:35:48,614 --> 00:35:52,816
More than double the number
in the milky way.
602
00:35:52,818 --> 00:35:56,620
This juggernaut
is hurtling towards us.
603
00:35:56,622 --> 00:35:59,789
The stage is set
for a mighty cosmic showdown.
604
00:36:02,761 --> 00:36:06,229
When will this clash
of the galactic titans happen?
605
00:36:08,333 --> 00:36:11,067
And what will it do
to the milky way?
606
00:36:11,069 --> 00:36:16,072
♪♪
607
00:36:17,576 --> 00:36:22,646
♪♪
608
00:36:22,648 --> 00:36:24,948
Narrator: Astronomers believe
the milky way is destined
609
00:36:24,950 --> 00:36:27,984
To collide with our galactic
neighbor, andromeda.
610
00:36:31,156 --> 00:36:34,758
They race to discover
when this mighty cosmic faceoff
611
00:36:34,760 --> 00:36:36,393
Will take place.
612
00:36:38,564 --> 00:36:39,963
Tremblay:
The milky way and andromeda
613
00:36:39,965 --> 00:36:42,599
Are two of the most massive
galaxies in our local group,
614
00:36:42,601 --> 00:36:44,668
And we know that they're
moving toward one another
615
00:36:44,670 --> 00:36:46,136
And will eventually collide.
616
00:36:46,138 --> 00:36:48,071
So what we want to discover now
617
00:36:48,073 --> 00:36:49,873
Is whether they're on
a direct collision course
618
00:36:49,875 --> 00:36:51,608
And they're headed
right for one another
619
00:36:51,610 --> 00:36:53,043
Or whether they're gonna
continue to dance
620
00:36:53,045 --> 00:36:56,813
Around each other
for several billion more years.
621
00:36:56,815 --> 00:37:00,050
Tremblay: Telescopes from around
the world scan andromeda
622
00:37:00,052 --> 00:37:04,554
To unlock its speed
and trajectory.
623
00:37:04,556 --> 00:37:07,090
They discover that andromeda
and the milky way
624
00:37:07,092 --> 00:37:09,092
Will smash into one another
625
00:37:09,094 --> 00:37:11,795
Within the next
five billion years.
626
00:37:14,733 --> 00:37:17,801
The result will be a period
of star creation
627
00:37:17,803 --> 00:37:21,871
Unmatched in the history
of our galaxy.
628
00:37:21,873 --> 00:37:23,940
Oluseyi: We now have the most
accurate prediction
629
00:37:23,942 --> 00:37:25,709
Of when this collision
is gonna take place,
630
00:37:25,711 --> 00:37:29,179
And when it does, it's gonna
set the skies alight
631
00:37:29,181 --> 00:37:32,382
Because there's gonna be
a huge burst of star formation.
632
00:37:36,355 --> 00:37:39,322
Narrator: The massive sizes of
the milky way and andromeda
633
00:37:39,324 --> 00:37:42,525
Give them huge gravity.
634
00:37:42,527 --> 00:37:44,828
The two galaxies speed
towards each other
635
00:37:44,830 --> 00:37:49,699
At over 250,000 miles per hour.
636
00:37:49,701 --> 00:37:54,704
Their gas reserves smash
together when they meet.
637
00:37:54,706 --> 00:37:58,308
This triggers a super intense
period of star creation.
638
00:38:01,780 --> 00:38:04,848
Billions of new stars
burst into life.
639
00:38:07,653 --> 00:38:12,355
The spiral arms of the milky way
and andromeda tangle together.
640
00:38:12,357 --> 00:38:18,928
They eventually form a giant
super galaxy called milkomeda.
641
00:38:18,930 --> 00:38:21,031
What a sight that will be.
642
00:38:21,033 --> 00:38:22,866
I mean, it's beautiful enough
going out now
643
00:38:22,868 --> 00:38:24,834
And seeing our galaxy as it is,
644
00:38:24,836 --> 00:38:28,705
But we're adding a whole
other galaxy to our own.
645
00:38:28,707 --> 00:38:31,408
There will be more stars,
more gas out there,
646
00:38:31,410 --> 00:38:35,312
More things to see,
more structures in the sky.
647
00:38:35,314 --> 00:38:37,747
It will be fantastic.
648
00:38:41,453 --> 00:38:43,920
Narrator: Today, a drop off
in star formation
649
00:38:43,922 --> 00:38:45,622
At the center of the milky way
650
00:38:45,624 --> 00:38:48,358
Means our galaxy
is losing its shine.
651
00:38:50,962 --> 00:38:52,696
The creation of milkomeda
652
00:38:52,698 --> 00:38:56,833
Will throw this galactic
dimming into reverse.
653
00:38:56,835 --> 00:39:00,036
This new galaxy will make
billions of bright, new stars
654
00:39:00,038 --> 00:39:04,708
In the space of
a few hundred million years.
655
00:39:04,710 --> 00:39:07,410
But scientists believe
that our galaxy will then move
656
00:39:07,412 --> 00:39:13,149
Into the final stage of its life
after this dramatic merger.
657
00:39:13,151 --> 00:39:15,485
The light
from a billion new stars
658
00:39:15,487 --> 00:39:17,587
Bursting into life so quickly
659
00:39:17,589 --> 00:39:21,558
Blasts away surplus gas.
660
00:39:21,560 --> 00:39:26,162
This prevents the birth
of new stars in the future.
661
00:39:26,164 --> 00:39:28,732
Oluseyi:
The formation of bright stars
662
00:39:28,734 --> 00:39:30,767
Is gonna drive out gas and dust,
663
00:39:30,769 --> 00:39:33,737
And then when the big stars
start exploding,
664
00:39:33,739 --> 00:39:35,905
That's gonna drive out
even more.
665
00:39:35,907 --> 00:39:40,043
So this birth may just lead
to the end of star formation
666
00:39:40,045 --> 00:39:41,845
In the galaxy.
667
00:39:41,847 --> 00:39:45,081
Tremblay: We think of galaxies
as these immortal structures,
668
00:39:45,083 --> 00:39:48,918
These vast swirling voids
of hundreds of billions of stars
669
00:39:48,920 --> 00:39:52,088
That live for all of time,
but in fact, it's not true.
670
00:39:52,090 --> 00:39:56,659
Galaxies change and evolve
and eventually die.
671
00:39:56,661 --> 00:39:59,529
Narrator: Milkomeda will inhabit
a sparsely populated part
672
00:39:59,531 --> 00:40:02,399
Of the universe.
673
00:40:02,401 --> 00:40:05,635
There will be no nearby galaxies
to feed from
674
00:40:05,637 --> 00:40:09,806
To rejuvenate
the lost gas supply.
675
00:40:09,808 --> 00:40:11,941
Oluseyi: Once the milky way
and andromeda merge
676
00:40:11,943 --> 00:40:13,676
And form a new, larger galaxy,
677
00:40:13,678 --> 00:40:16,379
It has this huge burst
of star formation.
678
00:40:16,381 --> 00:40:19,716
After that, things are gonna go
a lot quieter
679
00:40:19,718 --> 00:40:22,852
Because we're relatively
isolated right now.
680
00:40:22,854 --> 00:40:24,487
It's just the two of us.
681
00:40:26,591 --> 00:40:29,993
Narrator: Milkomeda is condemned
to terminal decline
682
00:40:29,995 --> 00:40:32,595
And extinction.
683
00:40:32,597 --> 00:40:34,798
After the giant galactic
fireworks show
684
00:40:34,800 --> 00:40:37,400
That will be the collision
of the milky way and andromeda,
685
00:40:37,402 --> 00:40:39,302
We're live
in this simmering ember
686
00:40:39,304 --> 00:40:42,672
That will continue to cool off
for billions of years more.
687
00:40:42,674 --> 00:40:45,775
Ultimately, our existence
as a civilization is nothing
688
00:40:45,777 --> 00:40:48,445
But a sentence
in the book of the universe.
689
00:40:51,249 --> 00:40:55,285
Narrator:
Astronomers are now unlocking
the life story of our milky way.
690
00:40:58,857 --> 00:41:00,123
Mega bubbles of gas
691
00:41:00,125 --> 00:41:03,993
Reveal how supermassive
black holes generate heat
692
00:41:03,995 --> 00:41:07,797
That stops star birth
and makes galaxies grow dim.
693
00:41:10,836 --> 00:41:14,204
Weird alien stars show
how galactic collisions
694
00:41:14,206 --> 00:41:17,774
Rejuvenate galaxies
and make them grow bright again.
695
00:41:20,312 --> 00:41:24,881
Today, the milky way is passing
through a phase of dimming.
696
00:41:24,883 --> 00:41:30,119
But the light show we see
from earth is still spectacular.
697
00:41:30,121 --> 00:41:32,222
Thaller: I want you to realize
that we live
698
00:41:32,224 --> 00:41:34,991
In this tremendously
fortunate time.
699
00:41:34,993 --> 00:41:37,594
Go outside
and look at the stars.
700
00:41:37,596 --> 00:41:39,762
Feel this joy seep through you.
701
00:41:39,764 --> 00:41:42,565
You are standing
in this wondrous moment.
702
00:41:42,567 --> 00:41:44,667
Enjoy it and celebrate it.
703
00:41:46,705 --> 00:41:50,006
Narrator:
The milky way will enter
a new stage of its evolution
704
00:41:50,008 --> 00:41:53,309
And five billion years' time --
705
00:41:53,311 --> 00:41:56,613
One final cosmic blowout.
706
00:41:56,615 --> 00:42:01,551
Before it slowly fades away
into the darkness.