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Narrator: We live in a galaxy
called the Milky Way,
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an empire with
hundreds of billions of stars.
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Dr. Krauss: How did we get here,
and what's our future?
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In every way, those questions
involve galaxies.
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Narrator: There are 200 billion
galaxies in the known universe,
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each one unique, enormous,
and dynamic.
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Dr. Kaku:
Galaxies are violent.
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They were born
in a violent history.
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They will die a violent death.
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Narrator:
Where do galaxies come from?
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How do they work?
What is their future?
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And how will they die?
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This is our galaxy,
the Milky Way.
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It's around
12 billion years old.
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The galaxy itself is a huge disk
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with giant spiral arms
and a bulge in the middle.
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It's just one of a huge number
of galaxies in the universe.
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Galaxies are,
first and foremost,
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large collections of stars.
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The average galaxy
may contain 100 billion stars.
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They're really
stellar nurseries,
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the place where stars are born
and where they also die.
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Narrator:
The stars in a galaxy are born
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in clouds of dust and gas
called nebulas.
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These are the pillars
of creation in the Eagle nebula,
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a star nursery
deep in the Milky Way.
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Our galaxy contains
many billions of stars,
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and around many of them
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are systems
of planets and moons.
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But for a long time, we didn't
know much about galaxies.
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Just a century ago,
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we thought that the Milky Way
was all there was.
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Scientists called it
our island universe.
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For them,
no other galaxies existed.
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Then, in 1924, astronomer
Edwin Hubble changed all that.
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Hubble was observing
the universe
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with the most advanced telescope
at the time,
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the 100-inch Hooker on
Mount Wilson near Los Angeles.
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Deep in the night sky,
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he saw fuzzy blobs of light
that were far, far away.
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He realized they weren't
individual stars at all.
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They were
whole cities of stars --
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galaxies
way beyond the Milky Way.
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Astronomers
had an existential shock.
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In one year,
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we went from the universe
being the Milky Way galaxy
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to a universe
of billions of galaxies.
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Narrator: Hubble had made
one of the greatest discoveries
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in the history of astronomy --
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the universe contains
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not just one
but a great number of galaxies.
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This is the Whirlpool galaxy.
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It has two giant spiral arms
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and contains
around 160 million stars.
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And Galaxy M87,
a giant elliptical galaxy --
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it's one of the oldest
in the universe,
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and the stars glow gold.
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And this is the Sombrero galaxy.
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It has a huge, glowing core
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with a ring of gas and dust
all around it.
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Dr. Kaku:
Galaxies are gorgeous.
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They represent, in some sense,
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the basic unit
of the universe itself.
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They're like gigantic pinwheels
twirling in outer space.
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It's like fireworks
created by Mother Nature.
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Narrator: Galaxies are big --
really, really big.
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On Earth,
we measure distance in miles.
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In space,
astronomers use light-years...
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The distance light travels
in a year.
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That's just under
6 trillion miles.
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Dr. Krauss:
Here we are,
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25,000 light-years away
from the center of our galaxy,
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and our galaxy is over
100,000 light-years across.
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But even that,
as large as it is,
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is kind of a speck
in the cosmic-distance scale.
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Narrator: Our Milky Way galaxy
may seem big to us,
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but compared to some others
out there...
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...it's actually pretty small.
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Andromeda,
our nearest galactic neighbor,
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is over 200,000
light-years across --
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twice the size of the Milky Way.
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M87 is the largest
elliptical galaxy
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in our own cosmic backyard,
and much bigger than Andromeda.
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But M87 is tiny
compared to this giant.
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6 million light-years across,
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IC 1011 is the biggest galaxy
ever found.
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It's 60 times larger
than our Milky Way.
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We know galaxies are big
and they're everywhere,
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but why is that?
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Dr. Strauss:
One of the very big questions
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we have in astrophysics
is where galaxies come from.
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We really don't have a complete
understanding of that.
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The universe started
in what we call a Big Bang,
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an extremely hot
and extremely dense phase
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about 13.7 billion years ago.
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We know that nothing
like a galaxy could have existed
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at that time.
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So galaxies must have been born,
they must have formed,
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out of that very early universe.
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Narrator:
It takes gravity to make stars
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and even more gravity to pull
stars together into galaxies.
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The first stars formed
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just 200 million years
after the Big Bang.
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Then gravity
pulled them together,
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building the first galaxies.
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The Hubble Space Telescope has
allowed us to peer back in time
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to almost the dawn of time...
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...the period when galaxies
have just begun to form.
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Narrator: The Hubble sees
lots of galaxies.
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But the light we see today
from those galaxies
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left there thousands, millions,
even billions of years ago.
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It's taken all that time
to reach us,
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so what we see today
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is the ancient history
of those galaxies.
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When we look
at the Hubble Deep Field,
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what we see are little smudges.
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They don't look much like
the galaxies we see today.
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They're just
little smudges of light
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that we can barely discern.
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Those smudges of light contain
millions or billions of stars
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that have just begun
to merge together.
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Narrator:
These faint smudges
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are the earliest galaxies
of all.
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They were formed
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around one billion years after
the beginning of the universe.
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But that's as far back
as Hubble can see.
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If we want
to go even further back in time,
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we need a different kind
of telescope --
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one too big
to launch into space.
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Well, now we have one, in the
high desert of northern Chile.
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This is ACT,
the Atacama Cosmology Telescope.
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At 17,000 feet,
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it's the highest ground-based
telescope in the world.
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Dr. Staggs:
I really like working
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in the extreme environment
of ACT.
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It's very, very cold often,
and the wind blows violently.
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But the good thing about it
from our point of view
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is that the sky is very,
very clear almost all the time.
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Narrator:
Clear skies are important
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for ACT's precise mirrors to
focus on the earliest galaxies.
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With ACT, we're able to zoom in
with unprecedented detail
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on parts of the sky.
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We can also study the progress
of growth of structures,
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where structures
are things like galaxies
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and clusters of galaxies,
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with a very fine-scale detail.
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Narrator: ACT doesn't detect
visible light.
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It detects cosmic microwaves
from the time
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the universe was just a few
hundred thousand years old.
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The telescope not only detects
early galaxies --
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it actually sees how they grew.
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We're able to track the progress
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of the formations of galaxies
and clusters of galaxies.
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We see the footprints of all
the galaxies that have grown
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in the time between
when the universe was
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a few hundred thousand
years old till now.
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Narrator: ACT has helped
astronomers understand
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how galaxies have evolved
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since almost
the beginning of time itself.
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[indistinct conversation]
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Dr. Strauss: And we can start
answering the question,
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what did galaxies look like
when they were young?
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How did they compare
with modern-day galaxies?
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How have they grown?
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Narrator: Astronomers are seeing
how galaxies evolve
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from groups of stars
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into the patchwork of systems
we see today.
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Our current understanding
is that stars form clusters
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that build into galaxies
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that build
into clusters of galaxies
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that build
into superclusters of galaxies,
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the largest structures we
observe in the universe today.
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Narrator:
Early galaxies were a mess --
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lumpy bunches
of stars, gas, and dust.
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Buttoday
galaxies look neat and orderly.
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So, how do messy galaxies
transform
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into beautiful spirals
and pinwheels?
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The answer is gravity.
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Gravity shapes galaxies
and controls their future.
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There is
an unimaginably powerful
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and incredibly destructive
source of gravity
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at the heart
of most galaxies.
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And there's one buried
deep at the center
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of our own Milky Way.
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Narrator: Galaxies have existed
for over 12 billion years.
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We know
these vast empires of stars
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come in all shapes and sizes,
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from swirling spirals
to huge balls of stars.
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00:11:54,214 --> 00:11:58,583
But there's still a lot
about galaxies we don't know.
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How did galaxies come to have
the shapes they do?
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Was a spiral galaxy
always a spiral galaxy?
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The answer
is almost certainly no.
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Narrator: Very young galaxies
are messy and chaotic,
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a jumble
of stars, gas, and dust.
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Then, over billions of years,
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they evolve
into neat, organized structures,
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like the Whirlpool galaxy...
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Or our own Milky Way.
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Our Milky Way began not as
a single baby galaxy, but many.
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What is now our Milky Way
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was once comprised
of lots of small structures,
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irregularly shaped objects
that began to merge.
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Narrator: The thing that pulls
the small structures together
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is gravity.
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Gradually,
it pulls stars inward.
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They begin spinning
faster and faster
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and flatten into a disk.
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Stars and gas are swept
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into huge spiral arms.
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This process was repeated
billions and billions of times
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across the universe.
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Each of these galaxies
looks different,
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but they do have
one thing in common --
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they all seem to orbit
something at their center.
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For years, scientists wondered
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what could be powerful enough
to change how a galaxy behaves.
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They found out -- a black hole.
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And not just
any kind of black hole --
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a supermassive black hole.
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The first clue that supermassive
black holes existed
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was that at the heart
of some galaxies,
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00:13:54,434 --> 00:13:56,425
there was
an immense amount of energy
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emanating out from the center.
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What we're seeing is the black
holes in these galaxies
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feasting on the material
around them,
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00:14:04,277 --> 00:14:08,111
so it's like having
a huge Thanksgiving dinner.
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Narrator:
The meal is gas and stars,
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00:14:11,618 --> 00:14:16,249
and it's being eaten
by the supermassive black hole.
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00:14:16,256 --> 00:14:20,693
When black holes eat,
they sometimes eat too fast
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and spit their dinner
back out into space
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in beams of pure energy.
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It's called a quasar.
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When scientists see a quasar
blasting from a galaxy,
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00:14:39,879 --> 00:14:42,849
they know it has
a supermassive black hole.
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00:14:46,953 --> 00:14:52,016
But what about our galaxy?
There's no quasar here.
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Does that mean there's
no supermassive black hole?
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00:14:58,631 --> 00:15:00,827
Andrea Ghez and her team
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have spent the last 15 years
trying to find out.
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00:15:05,338 --> 00:15:07,102
Dr. Ghez:
So, the key to discovering
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00:15:07,107 --> 00:15:10,907
a supermassive black hole
at the center of our Milky Way
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is to watch how the stars move.
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The stars move
because of the gravity,
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just like the planets
orbiting the Sun.
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00:15:18,084 --> 00:15:22,055
Narrator: But the stars closest
to the center of the galaxy
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are hidden by clouds of dust.
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So Ghez used the giant
Keck telescope in Hawaii
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00:15:28,361 --> 00:15:31,262
to look through the clouds.
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00:15:31,264 --> 00:15:36,259
What she saw was a strange
and brutal place.
249
00:15:36,269 --> 00:15:38,397
Dr. Ghez:
Everything is more extreme
250
00:15:38,405 --> 00:15:39,930
at the center of our galaxy.
251
00:15:39,939 --> 00:15:41,407
Things move really fast.
252
00:15:41,408 --> 00:15:45,538
Stars are gonna be
whizzing by one another.
253
00:15:45,545 --> 00:15:47,377
It's windy.
It's violent.
254
00:15:47,380 --> 00:15:49,940
It's unlike
anyplace else in our galaxy.
255
00:15:52,952 --> 00:15:56,183
Narrator: Ghez and her team
began to take pictures
256
00:15:56,189 --> 00:16:01,093
of a few stars
orbiting near the center.
257
00:16:01,094 --> 00:16:03,563
Dr. Ghez: The task has been
to make a movie
258
00:16:03,563 --> 00:16:05,053
of the stars at the center,
259
00:16:05,064 --> 00:16:06,498
and so you have to be patient,
260
00:16:06,499 --> 00:16:09,196
because you take a picture,
and then you take another one,
261
00:16:09,202 --> 00:16:10,135
and you see it move.
262
00:16:12,172 --> 00:16:14,766
Narrator: The pictures
of the orbiting stars
263
00:16:14,774 --> 00:16:16,674
revealed something amazing.
264
00:16:18,578 --> 00:16:23,675
They were moving at
several million miles an hour.
265
00:16:23,683 --> 00:16:26,277
Dr. Ghez:
When we had the second picture
266
00:16:26,286 --> 00:16:29,381
was the most exciting point
in this experiment,
267
00:16:29,389 --> 00:16:34,384
because it was clear to us that
these stars were moving so fast
268
00:16:34,394 --> 00:16:37,694
that the supermassive-black-hole
hypothesis had to be right.
269
00:16:40,033 --> 00:16:42,263
Narrator:
And it was right.
270
00:16:42,268 --> 00:16:45,363
Ghez and her team tracked
the movement of the stars
271
00:16:45,371 --> 00:16:47,772
and pinpointed
what they were orbiting.
272
00:16:49,809 --> 00:16:52,437
There's only one thing
powerful enough
273
00:16:52,445 --> 00:16:55,073
to sling big stars around
like that --
274
00:16:55,081 --> 00:16:57,243
a supermassive black hole.
275
00:16:57,250 --> 00:17:00,083
Dr. Ghez: It's the gravity
of the supermassive black hole
276
00:17:00,086 --> 00:17:02,214
that makes these stars orbit,
277
00:17:02,222 --> 00:17:04,623
so the curvature
was the definitive proof
278
00:17:04,624 --> 00:17:07,821
of a supermassive black hole
at the center of our galaxy.
279
00:17:07,827 --> 00:17:12,162
Narrator: The black hole
at the center of the Milky Way
280
00:17:12,165 --> 00:17:17,296
is gigantic --
15 million miles across.
281
00:17:17,303 --> 00:17:20,739
So, is Earth in any danger?
282
00:17:20,740 --> 00:17:22,708
We are in absolutely no danger
283
00:17:22,709 --> 00:17:25,974
of being sucked into
our supermassive black hole.
284
00:17:25,979 --> 00:17:27,572
It's simply too far away.
285
00:17:31,317 --> 00:17:35,345
Narrator: In fact, the Earth
is 25,000 light-years away
286
00:17:35,355 --> 00:17:39,690
from the supermassive black hole
at the center of the Milky Way.
287
00:17:39,692 --> 00:17:43,322
That's many trillions of miles.
288
00:17:43,329 --> 00:17:46,663
The Earth is safe -- for now.
289
00:17:54,007 --> 00:17:56,203
Supermassive black holes may be
290
00:17:56,209 --> 00:17:59,076
the source
of huge amounts of gravity,
291
00:17:59,078 --> 00:18:03,413
but they don't have enough power
to hold galaxies together.
292
00:18:03,416 --> 00:18:06,351
In fact, according to
the laws of physics,
293
00:18:06,352 --> 00:18:08,320
galaxies should fly apart.
294
00:18:10,890 --> 00:18:12,449
So why don't they?
295
00:18:12,458 --> 00:18:15,450
Because there's something
out there
296
00:18:15,461 --> 00:18:19,898
even more powerful
than a supermassive black hole.
297
00:18:19,899 --> 00:18:24,803
It can't be seen, and it's
virtually impossible to detect.
298
00:18:24,804 --> 00:18:29,674
It's called dark matter,
and it's everywhere.
299
00:18:34,581 --> 00:18:35,810
Narrator:
Astronomers have figured out
300
00:18:35,815 --> 00:18:39,149
that supermassive black holes
live at the heart of galaxies
301
00:18:39,152 --> 00:18:44,090
and pull stars
at incredible speeds.
302
00:18:44,090 --> 00:18:45,182
But they're not strong enough
303
00:18:45,191 --> 00:18:50,152
to hold all the stars
in a gigantic galaxy together.
304
00:18:50,163 --> 00:18:54,259
So, what does
hold them together?
305
00:18:54,267 --> 00:18:55,530
It was a mystery
306
00:18:55,535 --> 00:18:58,732
until a maverick scientist
came up with the idea
307
00:18:58,738 --> 00:19:03,608
that something unknown
was at work.
308
00:19:03,610 --> 00:19:07,740
Back in the 1930s,
Swiss astronomer Fritz Zwicky
309
00:19:07,747 --> 00:19:13,652
wondered why galaxies
stayed together in groups.
310
00:19:13,653 --> 00:19:17,021
By his calculations, they didn't
generate enough gravity,
311
00:19:17,023 --> 00:19:21,290
so they should fly
away from each other.
312
00:19:21,294 --> 00:19:24,787
And so he said, "Well, I know
that they haven't flown apart.
313
00:19:24,797 --> 00:19:27,789
I see them all gathered together
in this nice collection.
314
00:19:27,800 --> 00:19:31,566
Therefore, something
must be holding them in place."
315
00:19:31,571 --> 00:19:34,871
But our own gravity
was just not strong enough.
316
00:19:34,874 --> 00:19:36,342
And so he concluded
317
00:19:36,342 --> 00:19:38,834
that it must be something which
nobody had detected before,
318
00:19:38,845 --> 00:19:39,903
nobody had thought about,
319
00:19:39,912 --> 00:19:42,040
and he gave it this
name, dark matter.
320
00:19:42,048 --> 00:19:44,983
And this is really
a stroke of genius.
321
00:19:47,553 --> 00:19:51,114
Fritz Zwicky
was decades ahead of his time,
322
00:19:51,124 --> 00:19:55,186
and that's why he grated
on the astronomical community.
323
00:19:55,194 --> 00:19:57,390
But, you know, he was right.
324
00:20:01,067 --> 00:20:03,627
Narrator: if what Zwicky called
dark matter
325
00:20:03,636 --> 00:20:05,536
held galaxies together
in groups,
326
00:20:05,538 --> 00:20:10,339
perhaps it also holds
individual galaxies together.
327
00:20:10,343 --> 00:20:15,008
To find out, scientists built
virtual galaxies in computers
328
00:20:15,014 --> 00:20:18,314
with virtual stars
and virtual gravity.
329
00:20:18,317 --> 00:20:20,445
We did a simulation
330
00:20:20,453 --> 00:20:26,222
where we put a lot of particles
in orbit in a flat disk,
331
00:20:26,225 --> 00:20:28,922
which was just like
the picture of our galaxy.
332
00:20:28,928 --> 00:20:32,626
And we expected to find that
we get a perfectly good galaxy,
333
00:20:32,632 --> 00:20:36,159
and we were looking to see
if it had a spiral or whatnot.
334
00:20:36,169 --> 00:20:39,298
But we found
it always came apart.
335
00:20:39,305 --> 00:20:41,933
Narrator: There just wasn't
enough gravity in the galaxy
336
00:20:41,941 --> 00:20:43,409
to hold it together.
337
00:20:43,409 --> 00:20:47,141
So Ostriker then added
extra gravity,
338
00:20:47,146 --> 00:20:49,581
from virtual dark matter.
339
00:20:49,582 --> 00:20:51,277
It seemed like
a natural thing to try.
340
00:20:51,284 --> 00:20:52,945
And it solved the problem.
It fixed it.
341
00:20:54,687 --> 00:20:59,523
Narrator: Gravity from dark
matter held the galaxy together.
342
00:20:59,525 --> 00:21:01,289
Dr. Benson:
Dark matter acts
343
00:21:01,294 --> 00:21:04,025
as a sort of protective
scaffolding for galaxies
344
00:21:04,030 --> 00:21:06,795
that really holds them up
and holds them in place
345
00:21:06,799 --> 00:21:08,995
and prevents them
from falling apart.
346
00:21:09,001 --> 00:21:11,971
Narrator:
Now scientists are discovering
347
00:21:11,971 --> 00:21:15,874
that dark matter doesn't just
hold galaxies together --
348
00:21:15,875 --> 00:21:19,140
it might have sparked them
into life.
349
00:21:19,145 --> 00:21:22,171
Dr. Kaku: We think
that dark matter was created
350
00:21:22,181 --> 00:21:23,512
out of the Big Bang,
351
00:21:23,516 --> 00:21:25,780
and dark matter began to clump,
352
00:21:25,785 --> 00:21:28,516
and these clumpings
of dark matter
353
00:21:28,521 --> 00:21:32,617
eventually became the nuclei,
the seeds, for our galaxy.
354
00:21:32,625 --> 00:21:35,458
Narrator: But scientists
still have no idea
355
00:21:35,461 --> 00:21:38,158
what dark matter actually is.
356
00:21:38,164 --> 00:21:41,065
Dark matter is weird because
we don't understand it at all.
357
00:21:41,067 --> 00:21:43,126
It's clearly
not made of the same stuff
358
00:21:43,136 --> 00:21:44,501
that you and I are made of.
359
00:21:44,504 --> 00:21:47,235
You can't push against it.
You can't feel it.
360
00:21:47,240 --> 00:21:49,140
Yet it's probably all around us.
361
00:21:49,142 --> 00:21:51,304
It's a ghostlike material
362
00:21:51,310 --> 00:21:55,975
that will pass right through you
as if you didn't exist at all.
363
00:21:59,118 --> 00:22:01,985
Narrator: We might not know
much about dark matter,
364
00:22:01,988 --> 00:22:06,858
but the universe is full of it.
365
00:22:06,859 --> 00:22:09,624
So, the dark matter,
weight-for-weight,
366
00:22:09,629 --> 00:22:13,054
makes up at least six times
as much of the universe
367
00:22:13,065 --> 00:22:16,228
as does normal matter, the stuff
that we're all made from.
368
00:22:16,235 --> 00:22:17,737
And without it,
369
00:22:17,737 --> 00:22:21,105
the universe just wouldn't work
the way that it seems to work.
370
00:22:21,107 --> 00:22:22,905
Narrator:
But the universe does work,
371
00:22:22,909 --> 00:22:28,040
so maybe dark matter is real.
372
00:22:28,047 --> 00:22:29,412
Strange stuff,
373
00:22:29,415 --> 00:22:33,648
and recently, it's been detected
in deep space --
374
00:22:33,653 --> 00:22:38,591
not directly but by observing
what it does to light.
375
00:22:38,591 --> 00:22:44,291
It bends it in a process
called gravitational lensing.
376
00:22:44,297 --> 00:22:47,631
Gravitational lensing
really allows us to test
377
00:22:47,633 --> 00:22:49,624
the presence of dark matter.
378
00:22:49,635 --> 00:22:51,831
And the way that works is that,
379
00:22:51,838 --> 00:22:54,273
as a beam of light
from some distant galaxy
380
00:22:54,273 --> 00:22:55,604
is traveling towards us,
381
00:22:55,608 --> 00:22:58,339
if it passes by a large
collection of dark matter,
382
00:22:58,344 --> 00:23:01,109
its path will be deflected
around that dark matter
383
00:23:01,113 --> 00:23:02,478
by the gravitational pull.
384
00:23:04,917 --> 00:23:07,443
Narrator: When the
Hubble telescope looks
385
00:23:07,453 --> 00:23:08,852
deep into the universe,
386
00:23:08,855 --> 00:23:12,519
some galaxies do seem
distorted and stretched.
387
00:23:14,527 --> 00:23:18,794
That's caused by the dark
matter, which warps the image.
388
00:23:18,798 --> 00:23:22,826
It's sort of like
looking through a goldfish bowl.
389
00:23:22,835 --> 00:23:25,429
Dr. Benson: By probing
the shapes of those galaxies
390
00:23:25,438 --> 00:23:26,997
and the degree of distortion,
391
00:23:27,006 --> 00:23:29,304
we can really measure
very accurately
392
00:23:29,308 --> 00:23:31,606
the amount of dark matter
that's there.
393
00:23:34,380 --> 00:23:35,939
Narrator:
It's clear now
394
00:23:35,948 --> 00:23:38,883
that dark matter is a vital
ingredient of the universe.
395
00:23:41,020 --> 00:23:43,887
It's been working
since the dawn of time
396
00:23:43,890 --> 00:23:48,350
and affects
everything everywhere.
397
00:23:48,361 --> 00:23:51,353
It triggers
the birth of galaxies
398
00:23:51,364 --> 00:23:55,358
and keeps them
from falling apart.
399
00:23:55,368 --> 00:23:58,463
We can't see it or detect it,
400
00:23:58,471 --> 00:24:04,433
but, nevertheless, dark matter
is the master of the universe.
401
00:24:10,950 --> 00:24:13,612
Narrator:
Galaxies look isolated.
402
00:24:13,619 --> 00:24:16,919
It's true -- they are
trillions of miles apart.
403
00:24:16,923 --> 00:24:20,860
But, actually, they live
in groups called clusters.
404
00:24:23,029 --> 00:24:26,863
And these clusters of galaxies
are linked together
405
00:24:26,866 --> 00:24:31,303
in superclusters, containing
tens of thousands of galaxies.
406
00:24:31,304 --> 00:24:35,070
So, where does
our Milky Way galaxy fit in?
407
00:24:35,074 --> 00:24:37,736
Dr. Kaku: If you take a look
at the big picture,
408
00:24:37,743 --> 00:24:39,677
you realize that our galaxy
409
00:24:39,679 --> 00:24:43,138
is part of a local group
of galaxies, perhaps 30,
410
00:24:43,149 --> 00:24:45,641
and our galaxy and Andromeda
411
00:24:45,651 --> 00:24:49,713
are the two biggest galaxies
in this local group.
412
00:24:49,722 --> 00:24:52,316
But if you look
even farther out,
413
00:24:52,325 --> 00:24:57,593
we are part of the
Virgo supercluster of galaxies.
414
00:24:57,596 --> 00:24:59,530
Narrator:
Scientists are now mapping
415
00:24:59,532 --> 00:25:01,489
the overall structure
of the universe
416
00:25:01,500 --> 00:25:05,903
and the position of clusters
and superclusters of galaxies.
417
00:25:07,707 --> 00:25:10,108
[thunder crashes]
418
00:25:10,109 --> 00:25:14,239
This is Apache Point
Observatory in New Mexico,
419
00:25:14,246 --> 00:25:18,342
home to the Sloan
Digital Sky Survey, or SDSS.
420
00:25:20,820 --> 00:25:24,188
It's a small telescope
with a big price tag,
421
00:25:24,190 --> 00:25:26,215
and it has a unique mission.
422
00:25:35,701 --> 00:25:40,867
SDSS is building the first
3-D map of the night sky,
423
00:25:40,873 --> 00:25:44,366
a process that's identifying
the exact positions
424
00:25:44,377 --> 00:25:48,837
of tens of millions of galaxies.
425
00:25:50,449 --> 00:25:54,511
To do it,
SDSS goes galaxy hunting
426
00:25:54,520 --> 00:25:59,617
way out into space,
far beyond our Milky Way.
427
00:25:59,625 --> 00:26:03,721
It pinpoints
the positions of galaxies,
428
00:26:03,729 --> 00:26:07,996
and this information is copied
onto aluminum disks.
429
00:26:08,000 --> 00:26:12,198
Long: These aluminum disks
are about 30 inches across,
430
00:26:12,204 --> 00:26:14,764
and they have 640 holes each,
431
00:26:14,774 --> 00:26:17,141
and these holes correspond
432
00:26:17,143 --> 00:26:20,044
to the objects of interest
in the sky.
433
00:26:20,046 --> 00:26:22,538
Narrator:
Each object is a galaxy.
434
00:26:22,548 --> 00:26:25,347
Light from the galaxy
is channeled through a hole
435
00:26:25,351 --> 00:26:28,013
and down a fiberoptic cable.
436
00:26:28,020 --> 00:26:31,581
This method records data
on distance and position
437
00:26:31,590 --> 00:26:35,356
from thousands of galaxies
and plots their location in 3-D.
438
00:26:35,361 --> 00:26:38,092
Long: It's telling us
about their shape.
439
00:26:38,097 --> 00:26:40,532
It's telling us
about their makeup.
440
00:26:40,533 --> 00:26:43,366
It's telling us
how they're distributed.
441
00:26:43,369 --> 00:26:45,633
And all of this
is very important
442
00:26:45,638 --> 00:26:48,403
to astronomy
and understanding our universe.
443
00:26:50,509 --> 00:26:53,171
Narrator: And this
is what they're creating --
444
00:26:53,179 --> 00:26:56,342
the biggest 3-D map ever.
445
00:26:59,785 --> 00:27:03,915
The map is showing us things
we've never seen before.
446
00:27:03,923 --> 00:27:09,487
It shows galaxies
in clusters and superclusters...
447
00:27:09,495 --> 00:27:11,156
But pull back even more,
448
00:27:11,163 --> 00:27:14,599
and we see that these
superclusters are connected
449
00:27:14,600 --> 00:27:19,060
into structures
called filaments.
450
00:27:19,071 --> 00:27:21,369
SDSS has found one
451
00:27:21,373 --> 00:27:25,970
that's 1.4 billion
light-years across.
452
00:27:29,081 --> 00:27:31,573
It's called
the Great Sloan Wall,
453
00:27:31,584 --> 00:27:34,246
and it's
the largest single structure
454
00:27:34,253 --> 00:27:37,951
ever discovered
in the history of science.
455
00:27:40,192 --> 00:27:45,187
Long: You get a sense that
you are in something quite vast.
456
00:27:45,197 --> 00:27:47,564
You can see
the clusters and filaments
457
00:27:47,566 --> 00:27:49,227
as the data would scroll by.
458
00:27:49,235 --> 00:27:52,296
And, you know, each one
of these little, fuzzy spots
459
00:27:52,304 --> 00:27:55,296
were actually galaxies --
not stars but galaxies --
460
00:27:55,307 --> 00:27:57,935
and so you're seeing
whole clusters of these things.
461
00:27:57,943 --> 00:28:02,210
Narrator: SDSS is showing
galactic geography
462
00:28:02,214 --> 00:28:03,909
on a vast scale.
463
00:28:03,916 --> 00:28:07,511
Scientists have taken it
even further.
464
00:28:08,521 --> 00:28:13,391
They've built the whole universe
in a supercomputer.
465
00:28:13,392 --> 00:28:16,828
Here you can't see
individual galaxies.
466
00:28:16,829 --> 00:28:19,992
You can't even see
galaxy clusters.
467
00:28:19,999 --> 00:28:24,232
What you can see
are superclusters,
468
00:28:24,236 --> 00:28:29,902
linked together on filaments
in a vast cosmic web.
469
00:28:29,909 --> 00:28:31,866
Dr. Krauss:
As one begins to come back
470
00:28:31,877 --> 00:28:33,811
from the whole scale
of the universe,
471
00:28:33,812 --> 00:28:36,213
one begins to reveal
a filamentary pattern,
472
00:28:36,215 --> 00:28:40,311
a cosmic web
containing galaxies
473
00:28:40,319 --> 00:28:43,380
and clusters of galaxies
that light up the universe
474
00:28:43,389 --> 00:28:45,255
where there are as many
galaxies in that direction
475
00:28:45,257 --> 00:28:47,453
as that direction as that
direction as that direction.
476
00:28:47,459 --> 00:28:49,928
And, in fact, on larger scales,
477
00:28:49,929 --> 00:28:53,354
the universe
kind of looks like a sponge.
478
00:28:53,365 --> 00:28:56,232
Narrator:
Each of the filaments is home
479
00:28:56,235 --> 00:28:58,397
to millions of galaxy clusters,
480
00:28:58,404 --> 00:29:02,272
all bound together
by dark matter.
481
00:29:02,274 --> 00:29:04,709
In this computer simulation,
482
00:29:04,710 --> 00:29:08,442
the dark matter glows
along the filaments.
483
00:29:08,447 --> 00:29:12,350
Dark matter affects where in
the universe galaxies will form.
484
00:29:12,351 --> 00:29:13,512
When we look at galaxies,
485
00:29:13,519 --> 00:29:15,385
they're not sprinkled around
at random.
486
00:29:15,387 --> 00:29:17,412
They actually tend to form
in little groups,
487
00:29:17,423 --> 00:29:19,755
and that's really reflecting
488
00:29:19,758 --> 00:29:23,524
the large-scale distribution
of dark matter.
489
00:29:23,529 --> 00:29:26,430
Narrator:
Dark matter is the glue
490
00:29:26,432 --> 00:29:31,063
holding together the whole
superstructure of the universe.
491
00:29:31,070 --> 00:29:34,802
It binds galaxies in clusters
492
00:29:34,807 --> 00:29:38,801
and clusters in superclusters.
493
00:29:38,811 --> 00:29:44,272
All these are locked together
in a web of filaments.
494
00:29:44,283 --> 00:29:45,751
Without dark matter,
495
00:29:45,751 --> 00:29:48,345
the whole structure
of the universe
496
00:29:48,354 --> 00:29:51,415
would simply fall apart.
497
00:29:51,423 --> 00:29:55,087
This is the big picture
of our universe.
498
00:29:57,263 --> 00:30:00,665
It's a giant cosmic web.
499
00:30:00,666 --> 00:30:04,660
And hidden deep in one of these
filaments is the Milky Way.
500
00:30:04,670 --> 00:30:08,436
It's been around
for nearly 12 billion years.
501
00:30:12,211 --> 00:30:14,270
But in the future,
502
00:30:14,280 --> 00:30:19,980
it's going to be destroyed
in a gigantic cosmic collision.
503
00:30:29,128 --> 00:30:33,531
Narrator: Galaxies
are vast kingdoms of stars.
504
00:30:33,532 --> 00:30:36,331
Some are giant balls,
505
00:30:36,335 --> 00:30:39,236
and others, complex spirals.
506
00:30:39,238 --> 00:30:42,799
The thing is,
they never stop changing.
507
00:30:42,808 --> 00:30:45,573
While it may seem,
when we look out at our galaxy,
508
00:30:45,577 --> 00:30:49,741
that our galaxy is static
and been here forever, it's not.
509
00:30:49,748 --> 00:30:51,910
Our galaxy is a dynamic place.
510
00:30:51,917 --> 00:30:55,547
Its very nature has been
changing over cosmic time.
511
00:30:57,923 --> 00:31:02,326
Narrator: Galaxies not only
change -- they move, as well.
512
00:31:05,197 --> 00:31:07,757
And sometimes
they run into each other.
513
00:31:07,766 --> 00:31:12,533
And when they do,
it's eat or be eaten.
514
00:31:15,574 --> 00:31:20,239
There's a zoo of galaxies
that you can find out there,
515
00:31:20,245 --> 00:31:23,237
and this entire zoo
can interact or collide
516
00:31:23,248 --> 00:31:26,047
with any of the other members
of the zoo.
517
00:31:28,120 --> 00:31:32,648
Narrator:
This is NGC 2207.
518
00:31:32,658 --> 00:31:37,255
It looks like an enormous
double-spiral galaxy,
519
00:31:37,262 --> 00:31:42,701
but it's actually
two galaxies colliding.
520
00:31:42,701 --> 00:31:45,830
The collision will last
millions of years,
521
00:31:45,838 --> 00:31:50,002
and eventually the two galaxies
will become one.
522
00:31:54,079 --> 00:31:57,379
Collisions like this happen
all over the universe.
523
00:31:57,383 --> 00:32:02,344
Our own Milky Way
is no exception.
524
00:32:02,354 --> 00:32:06,052
The Milky Way is, in fact,
a cannibal,
525
00:32:06,058 --> 00:32:08,789
and it exists
in its present form
526
00:32:08,794 --> 00:32:11,786
by having cannibalized
small galaxies
527
00:32:11,797 --> 00:32:13,765
that it literally ate up.
528
00:32:13,766 --> 00:32:16,360
And today we can see
small streams of stars
529
00:32:16,368 --> 00:32:19,167
that are left over
from the most recent mergers
530
00:32:19,171 --> 00:32:21,469
that have formed
the Milky Way galaxy.
531
00:32:24,276 --> 00:32:28,179
Narrator: But that's nothing
compared to what's coming up.
532
00:32:28,180 --> 00:32:33,812
We are on a collision course
with the galaxy Andromeda.
533
00:32:33,819 --> 00:32:37,949
And for the Milky Way,
that's bad news.
534
00:32:40,559 --> 00:32:44,223
Our Milky Way galaxy
is approaching Andromeda
535
00:32:44,229 --> 00:32:47,893
at the rate of about a quarter
of a million miles per hour,
536
00:32:47,900 --> 00:32:51,268
which means that in 5 billion
to 6 billion years,
537
00:32:51,270 --> 00:32:54,262
it's all over
for the Milky Way galaxy.
538
00:32:54,273 --> 00:32:58,938
You would see
the entire Andromeda galaxy
539
00:32:58,944 --> 00:33:03,347
speeding towards us, really
barreling straight into us.
540
00:33:03,348 --> 00:33:05,442
As the two galaxies interact,
541
00:33:05,451 --> 00:33:08,512
they both become
more and more disturbed
542
00:33:08,520 --> 00:33:10,750
and closer and closer together.
543
00:33:10,756 --> 00:33:13,589
And the whole process
starts to snowball.
544
00:33:13,592 --> 00:33:16,584
The two galaxies
will enter a death dance.
545
00:33:16,595 --> 00:33:20,589
Narrator: This is a simulation
of the future collision,
546
00:33:20,599 --> 00:33:22,966
sped up millions of times.
547
00:33:27,372 --> 00:33:29,773
As the galaxies crash together,
548
00:33:29,775 --> 00:33:34,269
clouds of gas and dust are
thrown out in all directions.
549
00:33:42,387 --> 00:33:44,913
Gravity
from the merging galaxies
550
00:33:44,923 --> 00:33:50,453
rips stars from their orbits
and shoots them deep into space.
551
00:33:50,462 --> 00:33:52,897
Dr. Kaku:
As we approach doomsday
552
00:33:52,898 --> 00:33:56,334
for the Milky Way galaxy,
it would be spectacular.
553
00:33:56,335 --> 00:33:58,394
We would have a front-row seat
554
00:33:58,403 --> 00:34:01,065
on the destruction
of our own galaxy.
555
00:34:04,176 --> 00:34:08,204
And eventually, the two galaxies
will go right through each other
556
00:34:08,213 --> 00:34:11,444
and then come back
and then coalesce.
557
00:34:11,450 --> 00:34:16,115
Narrator: It's strange, but the
stars themselves won't collide.
558
00:34:16,121 --> 00:34:19,955
They're still too far apart.
559
00:34:19,958 --> 00:34:21,392
All of the stars are basically
560
00:34:21,393 --> 00:34:23,259
just gonna pass
right by each other.
561
00:34:23,262 --> 00:34:26,163
The probability
of one individual star
562
00:34:26,164 --> 00:34:29,828
hitting another individual star
are basically zero.
563
00:34:33,305 --> 00:34:36,764
Narrator: However, the gas
and dust between the stars
564
00:34:36,775 --> 00:34:38,277
will start to heat up.
565
00:34:38,277 --> 00:34:40,507
Eventually, it ignites,
566
00:34:40,512 --> 00:34:44,813
and the clashing galaxies
will glow white-hot.
567
00:34:46,885 --> 00:34:51,721
So, at a certain point,
the sky could be on fire.
568
00:34:55,661 --> 00:35:00,223
The Milky Way and Andromeda as
we know it will cease to exist,
569
00:35:00,232 --> 00:35:02,963
and Milkomeda will be born,
570
00:35:02,968 --> 00:35:06,802
and it will look like
a whole new galaxy.
571
00:35:18,350 --> 00:35:21,149
Narrator:
This new galaxy, Milkomeda,
572
00:35:21,153 --> 00:35:23,884
will become
a huge, elliptical galaxy
573
00:35:23,889 --> 00:35:26,358
without any arms
or spiral shape.
574
00:35:28,293 --> 00:35:31,627
There's no escaping
what's going to happen.
575
00:35:31,630 --> 00:35:35,362
The question is,
what's it mean for planet Earth?
576
00:35:35,367 --> 00:35:37,995
We may either be
thrown out into outer space
577
00:35:38,003 --> 00:35:43,874
when the arms of the Milky Way
galaxy are ripped apart,
578
00:35:43,875 --> 00:35:48,574
or we could wind up in
the stomach of this new galaxy.
579
00:35:48,580 --> 00:35:53,677
Narrator: Stars and planets will
be pushed all over the place,
580
00:35:53,685 --> 00:35:58,714
so this may well be
the end of planet Earth.
581
00:36:05,464 --> 00:36:10,197
Galaxies all over the universe
will continue to collide.
582
00:36:13,071 --> 00:36:16,097
But this age
of galactic cannibalism
583
00:36:16,108 --> 00:36:19,840
will eventually pass...
584
00:36:19,845 --> 00:36:23,179
Because there is
an even more destructive force
585
00:36:23,181 --> 00:36:24,410
in the universe,
586
00:36:24,416 --> 00:36:26,748
a force that nothing can stop.
587
00:36:30,822 --> 00:36:35,123
It will ultimately push galaxies
away from each other,
588
00:36:35,127 --> 00:36:39,894
stretching everything,
until the universe...
589
00:36:39,898 --> 00:36:42,390
Rips itself apart.
590
00:36:48,640 --> 00:36:49,698
Narrator:
Galaxies are home
591
00:36:49,708 --> 00:36:54,874
to stars, solar systems,
planets, and moons.
592
00:36:54,880 --> 00:37:00,011
Everything that's important
happens in galaxies.
593
00:37:00,018 --> 00:37:03,283
Dr. Krauss: Galaxies are
the lifeblood of the universe.
594
00:37:03,288 --> 00:37:06,053
We arose
because we live in a galaxy,
595
00:37:06,058 --> 00:37:07,355
and everything we can see
596
00:37:07,359 --> 00:37:09,885
and everything that matters
to us in the universe
597
00:37:09,895 --> 00:37:11,090
happens within galaxies.
598
00:37:12,898 --> 00:37:14,889
Narrator:
But the truth is,
599
00:37:14,900 --> 00:37:19,633
galaxies are delicate structures
held together by dark matter.
600
00:37:19,638 --> 00:37:22,266
Now scientists have found
another force
601
00:37:22,274 --> 00:37:23,935
at work in the universe.
602
00:37:23,942 --> 00:37:27,207
It's called dark energy.
603
00:37:27,212 --> 00:37:30,773
Dark energy has the opposite
effect of dark matter.
604
00:37:30,782 --> 00:37:34,844
Instead of binding galaxies
together, it pushes them apart.
605
00:37:34,853 --> 00:37:36,878
Dr. Krauss:
The dark energy,
606
00:37:36,888 --> 00:37:39,949
which we've only discovered
in the last decade,
607
00:37:39,958 --> 00:37:42,222
which is the dominant stuff
in the universe,
608
00:37:42,227 --> 00:37:43,422
is far more mysterious.
609
00:37:43,428 --> 00:37:45,795
We don't have the slightest idea
why it's there.
610
00:37:50,168 --> 00:37:53,263
Dr. Benson: What it's made from,
we don't really know.
611
00:37:53,271 --> 00:37:55,899
We know it's there,
but we don't really know
612
00:37:55,907 --> 00:37:57,409
what it is or what it's doing.
613
00:37:57,409 --> 00:37:59,776
Dark energy is really weird.
614
00:37:59,778 --> 00:38:03,339
It's as if
space has little springs in it
615
00:38:03,348 --> 00:38:07,649
which are causing things
to repel each other
616
00:38:07,652 --> 00:38:09,677
and push them apart.
617
00:38:09,688 --> 00:38:11,622
Narrator:
Far in the future,
618
00:38:11,623 --> 00:38:14,251
scientists think
that dark energy will win
619
00:38:14,259 --> 00:38:17,991
the cosmic battle
with dark matter.
620
00:38:17,996 --> 00:38:21,057
And that victory will start
to drive galaxies apart.
621
00:38:21,066 --> 00:38:24,001
Dr. Krauss: Dark energy's
gonna kill galaxies off.
622
00:38:24,002 --> 00:38:27,267
It's gonna do that by causing
all the galaxies to recede
623
00:38:27,272 --> 00:38:30,572
further and further away from us
until they're invisible,
624
00:38:30,575 --> 00:38:32,009
until they're moving
away from us
625
00:38:32,010 --> 00:38:33,273
faster than the speed of light.
626
00:38:33,278 --> 00:38:35,372
So, the rest of the universe
will literally disappear
627
00:38:35,380 --> 00:38:36,711
before our very eyes.
628
00:38:36,715 --> 00:38:40,083
Not today, not tomorrow,
but in perhaps a trillion years,
629
00:38:40,085 --> 00:38:42,952
the rest of the universe
will have disappeared.
630
00:38:42,954 --> 00:38:47,790
Narrator: Galaxies will become
lonely outposts in deep space.
631
00:38:51,730 --> 00:38:56,463
But that's not going to happen
for a very, very long time.
632
00:38:56,468 --> 00:38:59,961
For now,
the universe is thriving
633
00:38:59,971 --> 00:39:02,963
and galaxies are creating
the right conditions
634
00:39:02,974 --> 00:39:05,102
for life to exist.
635
00:39:05,110 --> 00:39:07,579
Without galaxies,
I wouldn't be here.
636
00:39:07,579 --> 00:39:08,978
You wouldn't be here.
637
00:39:08,980 --> 00:39:11,381
Perhaps life itself
wouldn't be here.
638
00:39:13,418 --> 00:39:15,113
Narrator: We're lucky.
639
00:39:15,120 --> 00:39:17,020
Life has only evolved on Earth
640
00:39:17,022 --> 00:39:19,582
because our tiny solar system
was born
641
00:39:19,591 --> 00:39:21,559
in the right part of the galaxy.
642
00:39:24,529 --> 00:39:27,055
If we were
any closer to the center,
643
00:39:27,065 --> 00:39:30,228
well, we wouldn't be here.
644
00:39:32,270 --> 00:39:34,534
Dr. Kaku:
At the center of a galaxy,
645
00:39:34,539 --> 00:39:36,303
life can be extremely violent.
646
00:39:36,308 --> 00:39:39,107
And, in fact,
if our solar system were closer
647
00:39:39,110 --> 00:39:40,805
to the center of our galaxy,
648
00:39:40,812 --> 00:39:44,214
it would be so radioactive
that we couldn't exist at all.
649
00:39:44,216 --> 00:39:49,518
Narrator: Too far away from
the center would be just as bad.
650
00:39:53,291 --> 00:39:57,091
Out there,
there aren't as many stars.
651
00:39:57,095 --> 00:40:00,258
We might not exist at all.
652
00:40:00,265 --> 00:40:04,600
So, in some sense, we are in the
Goldilocks Zone of the galaxy --
653
00:40:04,603 --> 00:40:08,631
not too close, not too far,
but just right.
654
00:40:08,640 --> 00:40:10,665
Narrator:
Scientists believe
655
00:40:10,675 --> 00:40:13,042
that this galactic
Goldilocks Zone
656
00:40:13,044 --> 00:40:17,140
might contain millions of stars,
657
00:40:17,148 --> 00:40:21,745
so there may be other solar
systems that can support life
658
00:40:21,753 --> 00:40:24,085
right here in our own galaxy.
659
00:40:24,089 --> 00:40:26,854
And if our galaxy
has a habitable zone,
660
00:40:26,858 --> 00:40:28,952
then other galaxies could, too.
661
00:40:28,960 --> 00:40:31,429
Dr. Ghez:
The universe is immense,
662
00:40:31,429 --> 00:40:35,127
and the amazing thing is that
we're always discovering more.
663
00:40:35,133 --> 00:40:38,831
Every time we think we know
the answer to one problem,
664
00:40:38,837 --> 00:40:42,102
we find it's embedded
in a much bigger problem.
665
00:40:42,107 --> 00:40:43,506
And that's exciting.
666
00:40:46,111 --> 00:40:48,842
Narrator: There are
endless questions to ask
667
00:40:48,847 --> 00:40:50,941
and mysteries to solve...
668
00:40:50,949 --> 00:40:54,010
In our own galaxy,
the Milky Way,
669
00:40:54,019 --> 00:40:57,045
and in galaxies
all across the universe.
670
00:40:57,055 --> 00:40:58,853
10 years ago,
who would have thought
671
00:40:58,857 --> 00:41:00,450
that we would be able
to identify
672
00:41:00,458 --> 00:41:01,857
the black hole at the center?
673
00:41:01,860 --> 00:41:04,056
Who would have thought
10 years ago
674
00:41:04,062 --> 00:41:05,826
that the astronomical
community
675
00:41:05,830 --> 00:41:08,527
would believe in dark matter
and dark energy?
676
00:41:08,533 --> 00:41:10,160
Narrator:
More and more,
677
00:41:10,168 --> 00:41:14,264
scientific research
is focusing on galaxies.
678
00:41:14,272 --> 00:41:18,334
They hold the key
to how the universe works.
679
00:41:18,343 --> 00:41:20,835
We should be amazed
to live at this time, here,
680
00:41:20,845 --> 00:41:23,371
at a random time
in the history of the universe,
681
00:41:23,381 --> 00:41:26,817
on a random planet, at the
outskirts of a random galaxy,
682
00:41:26,818 --> 00:41:29,685
where we can ask questions
and understand things
683
00:41:29,688 --> 00:41:33,215
from the beginning
of the universe to the end.
684
00:41:33,224 --> 00:41:36,717
We should celebrate
our brief moment in the sun.
685
00:41:39,331 --> 00:41:42,699
Narrator:
Galaxies are born...
686
00:41:42,701 --> 00:41:46,126
They evolve...
687
00:41:46,137 --> 00:41:49,767
They collide...
688
00:41:49,774 --> 00:41:53,039
And they die.
689
00:41:53,044 --> 00:41:58,847
Galaxies are the superstars
of the scientific world.
690
00:41:58,850 --> 00:42:04,812
And even the scientists who
study them have their favorites.
691
00:42:04,823 --> 00:42:07,656
The Whirlpool galaxy, or M51.
692
00:42:11,629 --> 00:42:13,927
I kind of like
the Sombrero galaxy,
693
00:42:13,932 --> 00:42:16,401
if I had to put one on a wall.
694
00:42:16,401 --> 00:42:17,527
[laughs]
695
00:42:17,535 --> 00:42:20,869
Dr. Krauss: The Sombrero galaxy,
ring galaxies --
696
00:42:20,872 --> 00:42:22,772
they're just beautiful
to look at.
697
00:42:25,877 --> 00:42:29,142
My favorite galaxy
is the Milky Way galaxy.
698
00:42:29,147 --> 00:42:31,980
It's my true home.
699
00:42:41,126 --> 00:42:43,720
Narrator:
We're lucky that the Milky Way
700
00:42:43,728 --> 00:42:46,595
provides the right conditions
for us to live.
701
00:42:46,598 --> 00:42:51,968
Our destiny is linked to
our galaxy and to all galaxies.
702
00:42:55,840 --> 00:42:58,639
They made us, they shape us,
703
00:42:58,643 --> 00:43:02,238
and our future
is in their hands.
56710
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