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NARRATOR: The Milky Way galaxy...
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a vast cosmic city
of 200 billion stars.
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We live in a quiet neighborhood,
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tucked away in a safe neck
of the woods.
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But what if we could take our planet
on a journey across the galaxy?
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From the violent graveyards
where stars, billions of years old,
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go to die...
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to the cosmic cradles
where new stars burst to life.
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Dare to travel through
billions of years of space and time
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to find out how our galaxy
came to be...
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and the dark fate that awaits us.
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It's the ultimate journey
to uncover the secrets that lie...
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inside the Milky Way.
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Modern cities are a testament
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to some of the greatest accomplishments
of human civilization--
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feats of engineering that dazzle
with millions of lights.
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But the bright lights conceal
something even more amazing.
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Turn them off and behold...
a great city in the sky.
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JAMES BULLOCK: What is this?
Well, this is the Milky Way.
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This is our galaxy.
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Well, if you'd like, you could think
of the galaxy as a city of stars.
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NARRATOR: Our sun is just one
of the 200 billion stars
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that make up a vast cosmic city.
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A city we're just beginning to know.
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BULLOCK: It's really a wonderful time
to be an astronomer,
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especially in studies
of the Milky Way.
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We're undergoing something
of a revolution.
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In fact we can take you places
that are really quite remarkable.
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NARRATOR: We're about
to make a major move.
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We're picking up the earth
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and traveling across
thousands of light years--
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relocating to distant neighborhoods
of the galaxy.
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From our new address
the sky looks different...
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full of wonder and beauty...
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lit by a multitude of brilliant suns...
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...revealing the power of stars
that lived billions of years ago.
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Out here we'll get a glimpse of the future,
when our sun exists no more.
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It's a journey to unravel some
of the greatest mysteries of the universe:
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how the Milky Way was born,
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how it survived for so long
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and how it will eventually die.
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But before our trip can begin,
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we need a map
of where we're headed.
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And making one is the job
of astronomers
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like Robert Kirshner
and James Bullock.
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The first obstacle is simply figuring out
what kind of galaxy the Milky Way is.
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The Hubble Space Telescope
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gives astronomers the capability
to see billions of other galaxies.
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Each one is different.
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But it turns out there is a pattern.
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BULLOCK: When we look out to study
other galaxies in the universe,
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We see that there are basically
two types of galaxies.
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NARRATOR: The first type,
elliptical galaxies,
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appear as large balls of stars,
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and no matter what angle
they're viewed from,
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they always look rounded.
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The other main class is
the so-called "spiral galaxies,"
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because their stars are contained in arms
that spiral out from their centers.
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From a distance, a spiral galaxy
looks something like a Frisbee.
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The key to correctly
identifying the Milky Way
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is written across our night sky.
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BULLOCK: The Milky Way,
we believe, is a spiral galaxy.
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So what we're really seeing,
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when we look up at night at this band,
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is we're seeing our place
in the universe.
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We're part of a giant disc of stars.
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NARRATOR: But that's just
an insider's view.
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BULLOCK: Now, of course I can't show you
a picture of the galaxy in all its glory.
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We can't fly above the galaxy
and take a picture of it and show you.
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We're stuck in the disc of the galaxy,
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but we can still image it
from the ground.
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In fact, this image is a picture
of our galaxy, the Milky Way,
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taken from Earth.
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NARRATOR: This is one
of the most detailed images
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of our galaxy ever created.
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It's made from 800 million pixels
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contained in over a thousand
individual photographs,
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taken from the darkest
places on Earth.
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The photos have been painstakingly
stitched together
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to create this breathtaking view.
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But impressive as it is,
it's only part of the picture.
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ROBERT KIRSHNER:
It's something like a pizza.
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And if you were in the pizza,
if you were a pepperoni,
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your view would not be a very clear one
of what the whole story was.
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In the same way, we don't see
the whole reach of the Milky Way.
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NARRATOR: What astronomers
really need is a bird's eye view.
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KIRSHNER: You would need
to get out of the Milky Way
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to really see what it looks like.
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We don't have a way to do that,
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but we can look at other galaxies
and see what they look like.
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NARRATOR: Hubble's cameras capture
nearby galaxies in amazing detail--
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like Messier 74.
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Although it's over 30 million
light years away,
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it's one of our closest neighbors.
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Messier 74 is
a beautiful spiral galaxy.
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Its large, starry arms sweep out
from a bright core.
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BULLOCK: This is an example
of a galaxy
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that astronomers think looks
a lot like our galaxy, the Milky Way.
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This is a great representation
of our own star city.
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In the central region
we have the downtown.
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This is the bulge,
this bright spot in the middle,
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and from that we see,
spiraling out, these arms,
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these beautiful spiral structures
we see in this galaxy.
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NARRATOR: Astronomers compare
Hubble's incredibly detailed images
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of other spiral galaxies
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with the best images
of our own galaxy
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taken from the ground.
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Using satellites to measure
the distance and density
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of stars in different directions,
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astronomers reveal the grand plan
underlying our star city.
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At its heart, a bright central region--
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the galactic core--
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our galaxy's downtown district.
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From here two majestic spiral arms,
bright bands of billions of stars,
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sweep out--
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Scutum Centaurus
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and the Perseus arm.
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There are also three smaller arms.
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From one end to the other,
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our galaxy measures
a staggering 600,000 trillion miles.
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BULLOCK: It takes light 100,000 years
to cross our galaxy.
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This is a big galaxy,
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and it's quite amazing,
if you think about it,
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that we understand as much
as we do about this system.
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NARRATOR: Our sun and the solar system
are located here--
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in a quiet neighborhood
nestled between two spiral arms.
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This is the galactic home address
that we know so well.
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But our surrounding neighborhoods
are wildly different.
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Like any large city, there are
dynamic industrial zones...
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where heat and pressure
forge new stars
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and others die
in violent explosions.
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Downtown, in the very heart
of the galaxy,
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stars jostle for space,
pulled by mysterious forces.
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[people screaming]
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Our galaxy also has quaint,
historic neighborhoods
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that tell the story of how
our star city was founded.
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Now we head to one of the most spectacular
locations in the Milky Way--
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a place that holds the clue
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to how the 200 billion
stars of the galaxy
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were first created--
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and it's just around the corner.
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We're picking up and leaving home.
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We're taking our planet on a journey.
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The destination?
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A place where stars are born.
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It may look close by, but even
traveling at the speed of light--
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186,000 miles a second--
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the trip takes 1,500 years.
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We arrive at a vast glowing cloud
of gas and dust:
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the Great Orion Nebula.
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Beautiful new colors
fill our evening sky.
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But this cloud isn't
just a work of art.
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It holds the key to how our sun,
and every star in the galaxy,
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came to be.
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The Milky Way is filled with
billions of stars in every direction.
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From Earth the naked eye
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also picks out large, dark,
seemingly starless patches.
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To astronomer James Bullock,
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in these areas, there's more
than meets the eye.
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BULLOCK: Perhaps the most beautiful
part of this image
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is that we have this contrast
of dark and light regions
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running through the plane
of the disc.
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What that really is, it's dust.
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There are clouds of dust
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that are casting a shadow
from the back of the stars,
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and the stars are trying
to shine their light through,
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there are dust clouds there
that are blocking the light,
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much like a cloud on Earth
would block the Sun.
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NARRATOR: These vast clouds
of cosmic gas and dust
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stretch thousands of light years
across the Milky Way.
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Hubble finds them
in most spiral galaxies.
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Dark, ghostly bands,
woven through the spiral arms--
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and spreading across the entire disc.
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But there's something strange
about this gas and dust.
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Sometimes it glows.
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These bright glowing clouds
are called nebulas.
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Each one is unique...
and breathtakingly beautiful.
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The Eagle Nebula, with towering pillars
up to four light years in size,
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and the Carina Nebula,
with its distinctive green glow.
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These vibrant colors reveal
what gases nebulas are made of.
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KIRSHNER: So, for example,
if there's oxygen gas,
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you get a green glow.
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If there is hydrogen gas,
you get a red glow.
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So analyzing the light from a nebula
turns out to be very instructive.
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It tells us what's there, it tells us
what the physical conditions are,
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we can tell how dense it is,
how hot it is
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and what it's made of.
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We can find out a lot
about the neighborhood
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by looking at these clues that come
directly from the glowing gas.
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NARRATOR: The gases glow
at thousands of degrees,
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heated from a mysterious source
hidden deep within the nebulas.
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To figure out what the source is,
we need to peer deep inside.
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KIRSHNER: But of course
the gas and dust is in the way.
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So it's not so easy.
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It's a very mysterious part
of the galaxy.
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It's a place that we have to use
these special tricks to look into.
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NARRATOR: And Kimberly Weaver
is an astrophysicist
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who's got a few tricks
up her sleeve.
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KIMBERLY WEAVER: I've got
a really neat way to show you this.
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This is a bag that you can't see through
with your eye.
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So a normal telescope that
looks at optical light
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could not see through this.
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00:16:45,250 --> 00:16:49,253
In infrared light, a telescope
can see through it.
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00:16:49,288 --> 00:16:50,688
The infrared camera,
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if I put my hand inside,
can see my hand.
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00:16:54,493 --> 00:16:57,261
I'll wiggle my fingers
to show you.
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00:16:57,296 --> 00:17:01,098
But you're seeing the heat
from my hand inside the bag,
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00:17:01,133 --> 00:17:06,070
and this is just like a star that's
hidden inside a cloud of gas and dust,
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00:17:06,104 --> 00:17:10,775
that infrared astronomers can detect
by using an infrared telescope.
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00:17:13,779 --> 00:17:18,149
This is a picture of the Orion Nebula
in visible light.
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We can see all of the gas here
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located in front of what we know
are stars in the background,
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00:17:24,523 --> 00:17:29,527
and we want to be able to look inside
this nebula and see the stars.
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00:17:29,561 --> 00:17:31,796
In infrared light, in this image,
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00:17:31,830 --> 00:17:36,634
we can now pick out the stars
inside the nebula,
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00:17:36,668 --> 00:17:41,105
and we can see dusty cocoons
around the stars.
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00:17:41,139 --> 00:17:47,044
NARRATOR: But scientists still need
a way to strip away the remaining dust.
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WEAVER: How do we get rid
of all this haze and fog?
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00:17:52,551 --> 00:17:55,186
The way to do that is
with an X-ray picture.
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00:17:55,220 --> 00:17:57,955
Now when we transition
into the X-ray image,
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00:17:57,990 --> 00:18:00,258
you can see just
the stars themselves,
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00:18:00,292 --> 00:18:03,527
the X-rays coming
from the surfaces of the stars,
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00:18:03,562 --> 00:18:06,631
and now we can study them
in great detail.
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00:18:09,668 --> 00:18:12,536
NARRATOR: By analyzing the light
from these stars,
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00:18:12,571 --> 00:18:16,607
astronomers make
an astounding discovery.
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00:18:19,411 --> 00:18:26,017
Hidden within the Orion Nebula are some
of the youngest stars ever found--
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00:18:26,051 --> 00:18:29,987
stars just a few
hundred thousand years old--
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00:18:30,022 --> 00:18:34,191
a mere heartbeat
in the life of the galaxy.
229
00:18:34,226 --> 00:18:37,395
And it's not just the Orion Nebula.
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00:18:39,331 --> 00:18:45,736
Nebulas house baby stars
in every spiral arm of the galaxy.
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00:18:48,240 --> 00:18:51,375
BULLOCK: These regions
are the nurseries for new stars.
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00:18:51,410 --> 00:18:53,277
There are young stars
in these regions
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00:18:53,312 --> 00:18:56,047
that are heating up gas clouds
that surround them
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00:18:56,081 --> 00:18:59,684
and making those
gas clouds glow pink.
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00:18:59,718 --> 00:19:02,420
Stars are made out of gas, basically,
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00:19:02,454 --> 00:19:04,355
and our galaxy has gas.
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00:19:04,389 --> 00:19:06,424
In fact, our galaxy, you can think of it
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00:19:06,458 --> 00:19:08,526
as having an atmosphere
of gas and dust
239
00:19:08,560 --> 00:19:10,995
that surrounds all of the stars
that we see in the disc,
240
00:19:11,029 --> 00:19:15,099
and it's from this gas
that new stars are born.
241
00:19:15,133 --> 00:19:19,570
NARRATOR: By observing nebulas
at different stages in their evolution,
242
00:19:19,604 --> 00:19:25,743
the story of a star's birth
begins to emerge.
243
00:19:25,777 --> 00:19:32,450
It all starts inside a cold, dark cloud
of dust and hydrogen gas,
244
00:19:32,484 --> 00:19:36,921
where a quiet tug of war begins.
245
00:19:36,955 --> 00:19:41,559
The cloud wants to dissipate,
like smoke in the air,
246
00:19:41,593 --> 00:19:45,663
but gravity wants
to pull it together.
247
00:19:45,697 --> 00:19:47,031
KIRSHNER: They're in
a kind of balance
248
00:19:47,065 --> 00:19:52,670
between gravity pulling in
and gas pressure pushing back out.
249
00:19:52,704 --> 00:19:57,074
Gravity wins, and the material
crunches down into a disc
250
00:19:57,109 --> 00:20:01,812
that is the beginning
of becoming a star.
251
00:20:01,847 --> 00:20:04,281
NARRATOR: As gravity pulls
more and more gas
252
00:20:04,316 --> 00:20:06,917
towards the center of the disc,
253
00:20:06,952 --> 00:20:12,323
it gets denser and denser
and hotter and hotter....
254
00:20:15,894 --> 00:20:19,964
...until finally,
at 18 million degrees,
255
00:20:19,998 --> 00:20:24,101
a miraculous transformation
takes place.
256
00:20:24,136 --> 00:20:28,272
Hydrogen atoms fuse together
to form helium--
257
00:20:28,306 --> 00:20:34,145
and with a burst of nuclear energy,
a star begins to shine.
258
00:20:34,179 --> 00:20:39,183
KIRSHNER: These stars eventually get
their nuclear fires going in the core.
259
00:20:39,217 --> 00:20:41,419
And when they do, they heat up,
260
00:20:41,453 --> 00:20:44,321
they can expel the material
that's around them
261
00:20:44,356 --> 00:20:48,759
so that it kind of clears up
the neighborhood.
262
00:20:48,794 --> 00:20:51,896
NARRATOR: Over the next
few million years,
263
00:20:51,930 --> 00:20:58,202
winds blow the surrounding gas
into spectacular swirling patterns.
264
00:21:01,606 --> 00:21:05,142
KIRSHNER: It blows away the gas,
it blows away the dust
265
00:21:05,177 --> 00:21:07,211
and it lets us see
this beautiful new thing,
266
00:21:07,245 --> 00:21:09,246
this place where the star
has been born.
267
00:21:31,002 --> 00:21:33,571
NARRATOR: A human lifetime
is too short
268
00:21:33,605 --> 00:21:38,275
to witness the wonder of a star's birth
in the spiral arms.
269
00:21:38,310 --> 00:21:44,748
But by speeding up millions of years
of cosmic time into just a few seconds,
270
00:21:44,783 --> 00:21:48,319
we can see one star born
after another.
271
00:21:55,827 --> 00:22:00,865
Here and there are even more
brilliant flashes of light,
272
00:22:00,899 --> 00:22:05,436
coming from some of the most violent
and dangerous neighborhoods
273
00:22:05,470 --> 00:22:09,540
in the entire Milky Way galaxy.
274
00:22:09,574 --> 00:22:13,644
Here stars aren't born...
275
00:22:13,678 --> 00:22:15,412
they die.
276
00:22:28,193 --> 00:22:30,027
We're taking the Earth
277
00:22:30,061 --> 00:22:32,296
from the familiar neighborhood
of the sun
278
00:22:32,330 --> 00:22:35,432
to visit the wonders
of the Perseus Arm,
279
00:22:35,467 --> 00:22:40,137
nearly 6,500 light years away.
280
00:22:40,839 --> 00:22:46,577
Here lies one of the galaxy's
most beautiful sights--
281
00:22:46,611 --> 00:22:50,681
the Crab Nebula.
282
00:22:50,715 --> 00:22:58,322
Although it's made of gas and dust,
this nebula hasn't created stars...yet.
283
00:23:01,693 --> 00:23:03,627
But for Alex Filippenko,
284
00:23:03,662 --> 00:23:08,265
this area does represent
the industrial zone of our galaxy,
285
00:23:08,300 --> 00:23:13,437
where the building blocks of Earth
were manufactured long ago.
286
00:23:13,471 --> 00:23:17,708
ALEX FILIPPENKO: Look at that
molten iron. Holy moly!
287
00:23:17,742 --> 00:23:20,477
The Crab Nebula is a fascinating object.
288
00:23:20,512 --> 00:23:23,981
We see these very rapidly
expanding gases.
289
00:23:25,984 --> 00:23:30,421
NARRATOR: The crab may look static,
but gases are racing out from its center
290
00:23:30,455 --> 00:23:36,226
at over three million miles an hour,
291
00:23:36,261 --> 00:23:42,566
put into motion by a phenomenally
powerful and violent event in the past.
292
00:23:47,172 --> 00:23:49,873
FILIPPENKO: When we examine
the gases of the Crab Nebula,
293
00:23:49,908 --> 00:23:51,976
which are expanding outward,
294
00:23:52,010 --> 00:23:55,779
and we extrapolate that expansion
backward in time,
295
00:23:55,814 --> 00:23:58,382
we find that all of the gases
were at a common point
296
00:23:58,416 --> 00:24:01,518
about a thousand years ago.
297
00:24:05,190 --> 00:24:08,192
NARRATOR: Back on Earth,
a thousand years ago,
298
00:24:08,226 --> 00:24:12,229
early civilizations
watched the heavens.
299
00:24:12,263 --> 00:24:20,638
In 1054, Chinese manuscripts describe
the sudden arrival of a brilliant new star.
300
00:24:20,672 --> 00:24:28,045
It shines brighter than any other star,
so brightly it's visible during the day.
301
00:24:28,079 --> 00:24:32,282
But then it mysteriously disappears.
302
00:24:34,953 --> 00:24:40,224
Today, the Crab Nebula lies
in exactly the same part of the sky
303
00:24:40,258 --> 00:24:43,894
where the Chinese observed
their brilliant star.
304
00:24:46,164 --> 00:24:50,634
What they witnessed was
the moment the crab was born.
305
00:24:53,071 --> 00:24:54,638
FILIPPENKO: The Crab Nebula
was produced
306
00:24:54,673 --> 00:25:00,010
by the colossal titanic explosion
of a star at the end of its life.
307
00:25:00,045 --> 00:25:02,212
It's a supernova remnant.
308
00:25:04,749 --> 00:25:07,217
NARRATOR: The spiral arms
of our Milky Way
309
00:25:07,252 --> 00:25:11,822
are littered with these
colorful remnants.
310
00:25:11,856 --> 00:25:15,759
Tombstones of stars
that died violently
311
00:25:15,794 --> 00:25:20,564
in cataclysmic explosions
called supernovas.
312
00:25:23,668 --> 00:25:28,706
To figure out this mystery, astronomers
need to locate the next victim--
313
00:25:28,740 --> 00:25:32,643
a massive star at the brink of death.
314
00:25:34,713 --> 00:25:36,747
FILIPPENKO: Astronomers
are like detectives.
315
00:25:36,781 --> 00:25:39,683
We have to figure out
what's going on in the universe
316
00:25:39,718 --> 00:25:42,986
sometimes based on
a minimal number of clues,
317
00:25:43,021 --> 00:25:48,158
and in the case of most astronomers,
the clues come from only the light.
318
00:25:50,128 --> 00:25:53,731
NARRATOR: Andy Howell knows
catching light from a supernova
319
00:25:53,765 --> 00:25:56,734
is all about timing.
320
00:25:58,236 --> 00:26:01,405
ANDY HOWELL: Supernovae happen
about once every 70 years
321
00:26:01,439 --> 00:26:02,806
in a galaxy on average,
322
00:26:02,841 --> 00:26:05,175
so about the human lifetime.
323
00:26:05,210 --> 00:26:08,479
So chances are you're not going
to see one in your lifetime.
324
00:26:08,513 --> 00:26:11,515
In fact the last one in our galaxy
that anybody saw
325
00:26:11,549 --> 00:26:13,650
was about 400 years ago.
326
00:26:13,685 --> 00:26:15,853
So it's been a long time,
327
00:26:15,887 --> 00:26:18,622
and, you know, I study
supernovae for a living.
328
00:26:18,656 --> 00:26:24,027
I couldn't do this if I had to just
wait for one in our galaxy.
329
00:26:24,062 --> 00:26:26,964
NARRATOR: But thankfully
for Howell and Filippenko,
330
00:26:26,998 --> 00:26:29,867
there's no shortage of galaxies.
331
00:26:32,137 --> 00:26:36,874
HOWELL: So what we do is we look
at other galaxies, more distant galaxies.
332
00:26:36,908 --> 00:26:39,309
There are billions
of galaxies out there,
333
00:26:39,344 --> 00:26:43,680
and we see the supernovae
that happen in those galaxies.
334
00:26:43,715 --> 00:26:48,786
And if you look at 70 galaxies,
on average you'll find one a year.
335
00:26:48,820 --> 00:26:52,723
If you look at 700 galaxies,
you'll find ten a year, and so on.
336
00:26:52,757 --> 00:26:54,258
FILIPPENKO: There's power in numbers.
337
00:26:54,292 --> 00:27:00,764
If we look at thousands of galaxies,
we improve our odds tremendously.
338
00:27:00,799 --> 00:27:02,699
NARRATOR: This is a supernova
339
00:27:02,734 --> 00:27:06,837
that Filippenko and his colleagues
are lucky enough to catch--
340
00:27:06,871 --> 00:27:14,912
an exploding star on the outskirts
of a galaxy 55 million light years away.
341
00:27:14,946 --> 00:27:18,949
It briefly outshines
the entire galaxy--
342
00:27:18,983 --> 00:27:25,122
the light of a billion suns
distilled into one dying star.
343
00:27:27,058 --> 00:27:28,826
HOWELL: It takes supernova light
344
00:27:28,860 --> 00:27:31,695
a million, or even
a billion years to get here
345
00:27:31,729 --> 00:27:34,364
if they're millions or billions
of light years away.
346
00:27:34,399 --> 00:27:36,500
But they only shine
for about a month,
347
00:27:36,534 --> 00:27:39,770
so we have this little tiny window
to study these things
348
00:27:39,804 --> 00:27:42,406
before that light is gone forever.
349
00:27:42,440 --> 00:27:45,209
NARRATOR: In the workshop,
Howell and his team
350
00:27:45,243 --> 00:27:48,645
are busy preparing
their telescopes.
351
00:27:49,714 --> 00:27:52,549
HOWELL: Pretty cool.
WOMAN: That's right.
352
00:27:52,584 --> 00:27:54,885
HOWELL: We're building
a network of telescopes
353
00:27:54,919 --> 00:27:57,654
so that we can study supernovae
in greater numbers,
354
00:27:57,689 --> 00:28:01,225
in greater detail, than we've
ever been able to before.
355
00:28:03,461 --> 00:28:05,462
Let me show you the telescopes
we're building.
356
00:28:05,496 --> 00:28:07,931
These are the 0.4 meter telescopes
357
00:28:07,966 --> 00:28:09,833
and there are four of them here,
358
00:28:09,868 --> 00:28:13,337
and we're building them,
20 of them in total,
359
00:28:13,371 --> 00:28:15,172
and putting them
all around the world.
360
00:28:15,206 --> 00:28:17,941
So some of these first ones
will go to Chile,
361
00:28:17,976 --> 00:28:20,677
we have some in Hawaii already.
362
00:28:20,712 --> 00:28:22,479
So let me show you one
of the bigger telescopes
363
00:28:22,513 --> 00:28:24,414
we're building here.
364
00:28:24,449 --> 00:28:26,650
Here we have
the one meter telescope.
365
00:28:26,684 --> 00:28:28,485
We're building about fifteen.
366
00:28:28,519 --> 00:28:31,221
The mirror's not here yet, but this
is where it's going to go.
367
00:28:31,256 --> 00:28:34,191
That will reflect the light
we gather from the supernova.
368
00:28:34,225 --> 00:28:36,426
We have to be able to point
anywhere in the sky,
369
00:28:36,461 --> 00:28:39,763
and so you can see that the telescope
pivots along this axis,
370
00:28:39,797 --> 00:28:42,065
and this C ring moves.
371
00:28:45,169 --> 00:28:46,970
The great thing about
this kind of observing
372
00:28:47,005 --> 00:28:49,039
is that it's totally robotic,
373
00:28:49,073 --> 00:28:51,341
and I can just sit here
in Santa Barbara
374
00:28:51,376 --> 00:28:54,745
and have a beer and pizza
while the telescopes do their work.
375
00:28:54,779 --> 00:29:00,083
All new discoveries about supernovae
from all different places in the universe.
376
00:29:00,118 --> 00:29:03,086
NARRATOR: Once they've caught
the light of a dying star,
377
00:29:03,121 --> 00:29:05,555
the detective work begins.
378
00:29:07,358 --> 00:29:10,928
FILIPPENKO: We collect that light
and we analyze it in great detail
379
00:29:10,962 --> 00:29:13,430
in order to determine
what's going on,
380
00:29:13,464 --> 00:29:15,666
what's the chemical makeup
of the star,
381
00:29:15,700 --> 00:29:17,868
what's the pressure inside,
what's the temperature,
382
00:29:17,902 --> 00:29:20,437
what kind of nuclear reactions
are going on,
383
00:29:20,471 --> 00:29:22,439
how does a star explode.
384
00:29:22,473 --> 00:29:27,577
All of these things we figured out
through the analysis of light.
385
00:29:30,281 --> 00:29:34,484
NARRATOR: Astronomers deduce
that only stars with a huge mass
386
00:29:34,519 --> 00:29:36,620
go out with a bang.
387
00:29:39,223 --> 00:29:42,926
FILIPPENKO: A massive star has
a very interesting and vigorous life.
388
00:29:42,961 --> 00:29:46,496
Initially it fuses hydrogen
to form helium,
389
00:29:46,531 --> 00:29:47,831
and that produces energy.
390
00:29:47,865 --> 00:29:50,067
That makes the star shine.
391
00:29:50,101 --> 00:29:52,970
Then the ashes of that reaction,
the helium,
392
00:29:53,004 --> 00:29:55,539
fuse together to form
carbon and oxygen,
393
00:29:55,573 --> 00:29:57,574
releasing yet more energy.
394
00:29:57,608 --> 00:30:01,178
Then the carbon and oxygen
can fuse into still heavier elements,
395
00:30:01,212 --> 00:30:04,781
magnesium and sodium and neon
and things like that,
396
00:30:04,816 --> 00:30:08,986
and then silicon and sulfur,
and finally iron.
397
00:30:09,020 --> 00:30:14,424
NARRATOR: When it starts to make iron,
the giant star is doomed.
398
00:30:16,928 --> 00:30:20,864
In the core a fierce battle
takes place:
399
00:30:20,898 --> 00:30:25,135
energy pushes outwards,
holding it up,
400
00:30:25,169 --> 00:30:28,772
while gravity wants
to crush it inwards.
401
00:30:30,842 --> 00:30:37,180
The battle continues as the star
makes heavier and heavier elements--
402
00:30:37,215 --> 00:30:41,785
producing energy while
fending off total collapse.
403
00:30:45,089 --> 00:30:50,360
But once it starts to form iron,
the battle is lost.
404
00:30:54,632 --> 00:30:57,834
FILIPPENKO: Fusion of iron nuclei
into heavier things
405
00:30:57,869 --> 00:31:01,204
does not release energy,
it absorbs energy.
406
00:31:01,239 --> 00:31:03,540
So an iron core builds up,
407
00:31:03,574 --> 00:31:07,544
but finally it becomes
so massive that gravity wins.
408
00:31:07,578 --> 00:31:09,846
The iron core collapses.
409
00:31:09,881 --> 00:31:13,550
In less than a second
the outer layers collapse inward,
410
00:31:13,584 --> 00:31:17,354
then rebound and get blown
to smithereens.
411
00:31:37,608 --> 00:31:44,114
NARRATOR: But from this death
comes new life.
412
00:31:44,148 --> 00:31:48,585
[train horn blows]
413
00:31:58,763 --> 00:32:03,300
[horn blows]
414
00:32:03,334 --> 00:32:05,001
FILIPPENKO: We're at a foundry here,
415
00:32:05,036 --> 00:32:09,873
and they're pouring molten iron
from old machinery,
416
00:32:09,907 --> 00:32:13,376
and they're going to make parts
for new machines out of that iron.
417
00:32:13,411 --> 00:32:15,278
So they're recycling it.
418
00:32:15,313 --> 00:32:19,382
But all that iron was created
and ejected into the cosmos
419
00:32:19,417 --> 00:32:24,087
by gigantic stars that exploded
as supernovae.
420
00:32:25,823 --> 00:32:29,893
Those explosions created the iron,
ejected it into the cosmos,
421
00:32:29,927 --> 00:32:33,897
and then it got incorporated
into planetary systems like ours.
422
00:32:33,931 --> 00:32:40,604
But ultimately the atoms of iron
were created by exploding stars.
423
00:32:40,638 --> 00:32:46,810
NARRATOR: Supernovas are
the industrial zones of our star city--
424
00:32:46,844 --> 00:32:51,181
cosmic foundries
that forge new elements.
425
00:32:54,552 --> 00:32:56,753
In catastrophic explosions
426
00:32:56,787 --> 00:33:00,490
heavy elements are spewed out
into our galaxy,
427
00:33:00,525 --> 00:33:04,361
enriching it over billions of years.
428
00:33:04,395 --> 00:33:07,264
FILIPPENKO: So if some stars
were not to explode
429
00:33:07,298 --> 00:33:11,501
in the industrial zones
of galaxies like our Milky Way,
430
00:33:11,536 --> 00:33:15,505
then we wouldn't have these
industrial zones here on Earth.
431
00:33:15,540 --> 00:33:16,907
It all is linked.
432
00:33:16,941 --> 00:33:20,710
We're all linked to the cosmos.
433
00:33:20,745 --> 00:33:23,847
NARRATOR: Our lives today
are only possible
434
00:33:23,881 --> 00:33:28,752
because of events that happened
thousands of millions of years ago
435
00:33:28,786 --> 00:33:32,389
in the hearts of supernovas.
436
00:33:32,423 --> 00:33:35,492
[horn blows]
437
00:33:38,629 --> 00:33:43,366
FILIPPENKO: It's fascinating to realize
that the heavy elements in our bodies,
438
00:33:43,401 --> 00:33:46,870
the carbon in our cells,
the calcium in our bones,
439
00:33:46,904 --> 00:33:51,074
the oxygen that we breathe,
the iron in our red blood cells,
440
00:33:51,108 --> 00:33:54,578
all of those heavy elements
were synthesized,
441
00:33:54,612 --> 00:33:58,048
created through
nuclear reactions in stars
442
00:33:58,082 --> 00:34:02,619
and ejected into the cosmos
by supernovae.
443
00:34:06,924 --> 00:34:13,196
NARRATOR: But only a handful of stars
are massive enough to die as supernovas.
444
00:34:13,231 --> 00:34:19,469
Most stars, like our sun,
suffer a more gentle death.
445
00:34:19,503 --> 00:34:23,206
FILIPPENKO: Most stars don't die
in a cataclysmic explosion.
446
00:34:23,241 --> 00:34:26,076
Our own sun, for example,
a typical star,
447
00:34:26,110 --> 00:34:28,778
will die with a whimper,
not a bang.
448
00:34:33,684 --> 00:34:36,853
NARRATOR: Death comes
when the gravity pulling in
449
00:34:36,887 --> 00:34:42,292
finally succumbs
to the nuclear energy pushing out.
450
00:34:45,529 --> 00:34:51,501
When this happens, any star,
even our sun, will die.
451
00:34:53,804 --> 00:34:55,972
FILIPPENKO: In about
four or five billion years
452
00:34:56,007 --> 00:35:00,277
it'll grow into a much bigger star,
a star called a red giant,
453
00:35:00,311 --> 00:35:02,679
and the outer atmosphere of gases
454
00:35:02,713 --> 00:35:06,549
will be held so loosely
by the sun at that time
455
00:35:06,584 --> 00:35:12,188
that the gases will be blown away gently,
in what I call a cosmic burp.
456
00:35:14,225 --> 00:35:18,261
NARRATOR: These cosmic burps
leave behind dying stars
457
00:35:18,296 --> 00:35:24,634
that litter the spiral arms as they
slowly shed layers of elements.
458
00:35:26,003 --> 00:35:29,306
HOWELL: Some layers are oxygen
and some layers are silicon
459
00:35:29,340 --> 00:35:31,274
and some layers are sulfur,
460
00:35:31,309 --> 00:35:33,209
and those are
the different colors we see
461
00:35:33,244 --> 00:35:35,979
in the Hubble Space Telescope images.
462
00:35:38,282 --> 00:35:44,287
NARRATOR: Not far from our sun
is a place where a star is dying:
463
00:35:44,322 --> 00:35:47,490
the Helix Nebula.
464
00:35:47,525 --> 00:35:52,395
It sheds light on how
most stars end their lives.
465
00:35:56,000 --> 00:36:00,203
Our sun is destined to follow
a similar path when it dies,
466
00:36:00,237 --> 00:36:03,173
five billion years from now.
467
00:36:08,145 --> 00:36:10,847
But in other neighborhoods
in the galaxy,
468
00:36:10,881 --> 00:36:14,484
stars suffer a fate
worse than death.
469
00:36:14,518 --> 00:36:16,019
At the center of the galaxy
470
00:36:16,053 --> 00:36:20,457
lies a place where stars
disappear altogether.
471
00:36:20,491 --> 00:36:25,095
[people screaming]
472
00:36:31,635 --> 00:36:35,238
We're taking the Earth
from the safety of home
473
00:36:35,272 --> 00:36:39,743
to go downtown,
to the heart of the Milky Way.
474
00:36:43,547 --> 00:36:50,720
It's a dynamic, exciting district,
but it's also a risky place to hang out.
475
00:36:50,755 --> 00:36:53,123
[screaming]
476
00:36:53,157 --> 00:36:59,195
Andrea Ghez has spent over 15 years
exploring this neighborhood.
477
00:37:00,464 --> 00:37:02,999
ANDREA GHEZ: If we were to take a trip
from the spiral arms,
478
00:37:03,033 --> 00:37:05,068
out where we are by the sun,
479
00:37:05,102 --> 00:37:08,405
down to the center of the galaxy,
it would be an interesting trip.
480
00:37:08,439 --> 00:37:11,374
It would be very much like
moving from the suburbs
481
00:37:11,409 --> 00:37:18,181
into the heart of a very busy
metropolitan area.
482
00:37:18,215 --> 00:37:23,753
NARRATOR: As we head downtown,
the number of stars increases.
483
00:37:23,788 --> 00:37:28,191
GHEZ: So the density of stars is
tremendous at the center of the galaxy.
484
00:37:28,225 --> 00:37:32,228
It's about a billion times higher
than out here by the sun.
485
00:37:35,065 --> 00:37:38,201
NARRATOR: Here, at the center
of the galaxy,
486
00:37:38,235 --> 00:37:41,504
there are so many stars in the sky
487
00:37:41,539 --> 00:37:45,341
that the Earth is bathed
in perpetual light.
488
00:37:48,312 --> 00:37:54,083
It's a stunning but dangerous
sight to behold.
489
00:37:54,118 --> 00:37:57,954
The stars aren't just close together.
490
00:37:57,988 --> 00:38:00,957
They're moving at super speed.
491
00:38:05,563 --> 00:38:06,996
GHEZ: Going to the heart
of the galaxy
492
00:38:07,031 --> 00:38:11,000
might not be dissimilar to going
to an amusement park.
493
00:38:11,035 --> 00:38:13,470
The rides are somewhat similar
494
00:38:13,504 --> 00:38:17,006
to how the stars orbit
the center of the galaxy.
495
00:38:18,909 --> 00:38:23,146
Ten million miles per hour,
compared to, say, our sun,
496
00:38:23,180 --> 00:38:27,217
is about a factor of 50 times faster.
497
00:38:27,251 --> 00:38:30,753
So something has to be going on
at the center of our galaxy
498
00:38:30,788 --> 00:38:32,922
to make that happen.
499
00:38:34,825 --> 00:38:39,128
NARRATOR: But figuring out what
is no small task.
500
00:38:39,163 --> 00:38:44,868
The heart of our galaxy lies
26,000 light years away.
501
00:38:44,902 --> 00:38:46,603
It's difficult to observe
502
00:38:46,637 --> 00:38:51,908
through the vast amounts
of stars, gas and dust.
503
00:38:51,942 --> 00:38:55,979
And there's another problem
even closer to home:
504
00:38:56,013 --> 00:38:58,681
the Earth's atmosphere.
505
00:39:00,217 --> 00:39:01,518
GHEZ: The atmosphere
is great for us.
506
00:39:01,552 --> 00:39:03,186
It allows us to survive
here on Earth,
507
00:39:03,220 --> 00:39:06,856
but it's an absolute headache
for astronomers.
508
00:39:06,891 --> 00:39:08,424
It's very much like the problem
509
00:39:08,459 --> 00:39:11,094
of looking at a pebble
at the bottom of a stream.
510
00:39:11,128 --> 00:39:13,963
The water in the stream
is moving by and it's turbulent
511
00:39:13,998 --> 00:39:16,699
and it makes it very difficult
to get a clear vision.
512
00:39:16,734 --> 00:39:19,202
In the same way, looking
through the Earth's atmosphere
513
00:39:19,236 --> 00:39:24,874
prevents us from getting clear pictures
of the stars at the center of the galaxy.
514
00:39:24,909 --> 00:39:26,943
NARRATOR:
So astronomers like Ghez
515
00:39:26,977 --> 00:39:30,480
turn to a technique
called adaptive optics
516
00:39:30,514 --> 00:39:33,583
to get a better view.
517
00:39:33,617 --> 00:39:38,288
By measuring how a laser beam
is distorted in moving air,
518
00:39:38,322 --> 00:39:42,992
it's possible to compensate
for the atmosphere's blurring effect.
519
00:39:44,361 --> 00:39:46,396
GHEZ: So let me show you
an example
520
00:39:46,430 --> 00:39:49,098
of how powerful
adaptive optics is.
521
00:39:49,133 --> 00:39:50,300
The stars that we want to see
522
00:39:50,334 --> 00:39:52,735
are the ones that are
at the very center,
523
00:39:52,770 --> 00:39:53,970
and we think the heart
of the galaxy
524
00:39:54,004 --> 00:39:57,640
is right within the center of this box,
which is panned out here.
525
00:39:57,675 --> 00:40:01,177
Without adaptive optics, this region
looks completely blurry.
526
00:40:01,211 --> 00:40:03,112
You don't see the individual stars.
527
00:40:03,147 --> 00:40:08,751
With adaptive optics
you see the individual stars.
528
00:40:08,786 --> 00:40:12,755
NARRATOR: For 15 years Ghez
has taken infrared images
529
00:40:12,790 --> 00:40:15,658
of the stars at the heart
of the galaxy
530
00:40:15,693 --> 00:40:20,863
to produce an extraordinary
time-lapse movie.
531
00:40:20,898 --> 00:40:23,399
GHEZ: So if we zoom in
to the very heart of the galaxy
532
00:40:23,434 --> 00:40:25,168
we can actually see
the data that we've taken
533
00:40:25,202 --> 00:40:26,869
over the last 15 years,
534
00:40:26,904 --> 00:40:28,271
and you can see the stars
535
00:40:28,305 --> 00:40:30,173
and you can see the tremendous motion
that they've gone through.
536
00:40:30,207 --> 00:40:33,610
in particular SO-2,
which is my favorite star--
537
00:40:33,644 --> 00:40:35,645
every astronomer
has a favorite one--
538
00:40:35,679 --> 00:40:37,714
so you can see SO-2
goes around
539
00:40:37,748 --> 00:40:40,850
and in particular you can see,
as it gets to the center of the frame,
540
00:40:40,884 --> 00:40:42,452
it moves much more quickly.
541
00:40:42,486 --> 00:40:45,355
So something's interesting
as it goes through that region.
542
00:40:45,389 --> 00:40:48,625
So putting everything together,
all the measurements that we've made,
543
00:40:48,659 --> 00:40:50,393
we've been able to make
an animation
544
00:40:50,427 --> 00:40:56,032
that shows how the stars have moved
over the course of 15 years.
545
00:40:56,066 --> 00:40:59,736
Each star goes whipping
around the center of the galaxy.
546
00:40:59,770 --> 00:41:02,472
in particular the most striking thing
that you'll notice
547
00:41:02,506 --> 00:41:05,708
is the motion of SO-2.
548
00:41:05,743 --> 00:41:09,379
So SO-2 goes on an incredible
roller coaster ride.
549
00:41:09,413 --> 00:41:13,282
it comes whipping around
and then back out.
550
00:41:13,317 --> 00:41:16,085
NARRATOR: For an object to have
enough gravitational pull
551
00:41:16,120 --> 00:41:21,924
to send SO-2 on rapid orbit
around the center of the galaxy...
552
00:41:21,959 --> 00:41:26,295
it must also have a huge mass.
553
00:41:31,802 --> 00:41:35,204
GHEZ: SO-2 goes around
once every 15 years,
554
00:41:35,239 --> 00:41:40,843
and what it tells us is that there
is four million times the mass of the sun
555
00:41:40,878 --> 00:41:43,746
confined within its orbit.
556
00:41:46,984 --> 00:41:49,886
NARRATOR: Astronomers know
of only one contender
557
00:41:49,920 --> 00:41:54,824
that has a giant mass
but is so small.
558
00:41:54,858 --> 00:41:57,060
GHEZ: So that's an incredible
amount of mass
559
00:41:57,094 --> 00:41:58,961
inside a very small volume,
560
00:41:58,996 --> 00:42:03,633
and that's the key
to proving a black hole.
561
00:42:03,667 --> 00:42:06,369
NARRATOR: And so at the center
of our galaxy
562
00:42:06,403 --> 00:42:09,372
lies a massive black hole,
563
00:42:09,406 --> 00:42:15,445
an object whose gravity is so strong
not even light can escape it.
564
00:42:18,148 --> 00:42:23,152
This is a real image
of the center of our galaxy.
565
00:42:24,521 --> 00:42:26,956
We can't see the black hole--
566
00:42:26,990 --> 00:42:33,930
but we can see bright clouds
of dust and gas spiraling toward it.
567
00:42:36,967 --> 00:42:39,702
We're nearing the black hole.
568
00:42:39,737 --> 00:42:44,307
It's at the center of a stream
of dust and gas...
569
00:42:46,977 --> 00:42:52,515
...the debris of stars blown apart
after straying too close.
570
00:42:56,720 --> 00:42:58,654
GHEZ: Black holes grow with time,
571
00:42:58,689 --> 00:43:02,024
and that happens
by material falling onto it,
572
00:43:02,059 --> 00:43:03,593
accreting onto it,
573
00:43:03,627 --> 00:43:06,863
and that material can come
in the form of either gas
574
00:43:06,897 --> 00:43:12,702
or stars that get torn apart
by the black hole itself.
575
00:43:12,736 --> 00:43:17,774
NARRATOR: At the center
is the invisible black hole.
576
00:43:17,808 --> 00:43:22,578
This is the material it feeds on.
577
00:43:22,613 --> 00:43:26,983
The glowing region
is the accretion disc.
578
00:43:27,017 --> 00:43:29,719
Here star debris falls inward
579
00:43:29,753 --> 00:43:33,055
and whips around
at astonishing speed.
580
00:43:33,090 --> 00:43:37,326
Friction heats the debris up
to such high temperatures
581
00:43:37,361 --> 00:43:40,963
that it glows white hot.
582
00:43:40,998 --> 00:43:43,432
GHEZ: So at the center of our galaxy
we do have a black hole.
583
00:43:43,467 --> 00:43:45,101
We now know that today,
584
00:43:45,135 --> 00:43:48,805
but it's not producing
a tremendous amount of energy.
585
00:43:48,839 --> 00:43:52,508
So it's perhaps, we could say,
it's a black hole that's on a diet.
586
00:43:52,543 --> 00:43:57,246
It simply doesn't have
a lot of material to feast on.
587
00:43:57,281 --> 00:44:01,384
NARRATOR: But what would happen
if SO-2 and the other stars
588
00:44:01,418 --> 00:44:05,521
were pulled inward
by the black hole?
589
00:44:05,556 --> 00:44:08,457
GHEZ: What happens when
that material falls onto the black hole
590
00:44:08,492 --> 00:44:09,959
is that the black hole,
591
00:44:09,993 --> 00:44:12,628
there's radiation associated
with the black hole
592
00:44:12,663 --> 00:44:14,697
and it can generate these jets,
593
00:44:14,731 --> 00:44:18,634
squirting out from the center
of the galaxy.
594
00:44:18,669 --> 00:44:22,939
NARRATOR: Spewing out subatomic particles
close to the speed of light,
595
00:44:22,973 --> 00:44:27,310
the beams are like
vast cosmic searchlights.
596
00:44:39,056 --> 00:44:41,624
This is Messier 87,
597
00:44:41,658 --> 00:44:48,030
a large elliptical galaxy that has
a super massive black hole at its heart.
598
00:44:48,065 --> 00:44:52,735
It's feasting on its own stars.
599
00:44:52,769 --> 00:44:55,171
Shooting out from its bright core
600
00:44:55,205 --> 00:44:59,809
are jets that travel
over 5,000 light years.
601
00:45:01,545 --> 00:45:05,114
GHEZ: I like to call these
the prima donnas of the galaxy world.
602
00:45:05,148 --> 00:45:09,552
These are the ten percent
of galaxies that are showoffs.
603
00:45:12,656 --> 00:45:15,825
NARRATOR: Astronomers believe
that the massive black hole
604
00:45:15,859 --> 00:45:17,560
at the heart of the Milky Way
605
00:45:17,594 --> 00:45:21,030
has been there from the very start.
606
00:45:23,433 --> 00:45:27,203
But in order to get back
to where the galaxy first began,
607
00:45:27,237 --> 00:45:33,376
we have to travel out to the oldest
neighborhood in our star city.
608
00:45:44,221 --> 00:45:48,257
We're traveling upward,
away from our solar system,
609
00:45:48,292 --> 00:45:52,962
out of the spiral arms
of our Milky Way.
610
00:45:52,996 --> 00:46:00,469
Up ahead lie vast clusters of stars
that orbit the heart of our star city.
611
00:46:03,040 --> 00:46:06,842
There are over 150 of them.
612
00:46:09,413 --> 00:46:13,683
These satellite towns,
called globular clusters,
613
00:46:13,717 --> 00:46:19,722
hold the answer to one of
the greatest mysteries in astronomy:
614
00:46:19,756 --> 00:46:23,559
the true age of our galaxy.
615
00:46:26,596 --> 00:46:30,466
BULLOCK: Globular clusters are
really fascinating groups of stars.
616
00:46:30,500 --> 00:46:32,969
They contain about
a million stars each,
617
00:46:33,003 --> 00:46:35,071
and the thing that's
really cool about them
618
00:46:35,105 --> 00:46:39,775
is the stars are
really tightly packed.
619
00:46:39,810 --> 00:46:41,344
KIRSHNER: If you could visit
a globular cluster,
620
00:46:41,378 --> 00:46:44,447
the night sky would be
spectacular,
621
00:46:44,481 --> 00:46:48,417
where many of the stars would be
as bright as the full moon.
622
00:46:48,452 --> 00:46:53,122
And the nighttime sky in all directions
would be filled with bright nearby stars.
623
00:46:53,156 --> 00:46:55,558
There'd be like fireworks all the time.
624
00:46:58,829 --> 00:47:01,664
NARRATOR: Besides the sheer
number of stars,
625
00:47:01,698 --> 00:47:06,902
there's something even more intriguing
about these clusters.
626
00:47:06,937 --> 00:47:08,971
BULLOCK: One of the very interesting
aspects of globular clusters
627
00:47:09,006 --> 00:47:13,209
is there's no sign of young stars.
628
00:47:15,912 --> 00:47:19,982
NARRATOR: Stars are like people.
629
00:47:20,017 --> 00:47:24,487
Look at them,
and you can guess their age
630
00:47:24,521 --> 00:47:28,424
and the lives they've led.
631
00:47:28,458 --> 00:47:34,130
With people, gray hairs and wrinkles
are the telltale signs.
632
00:47:34,164 --> 00:47:37,967
With stars, it's color and size.
633
00:47:40,037 --> 00:47:42,004
BULLOCK: So the biggest stars,
the most massive stars,
634
00:47:42,039 --> 00:47:45,408
the ones with the most gas,
live life in the fast lane.
635
00:47:45,442 --> 00:47:47,543
They live very short
amounts of time.
636
00:47:47,577 --> 00:47:50,413
But they burn very brightly
and they're very, very hot,
637
00:47:50,447 --> 00:47:53,616
and so they tend to be blue.
638
00:47:53,650 --> 00:47:55,918
KIRSHNER: On the other hand
you have the red stars,
639
00:47:55,952 --> 00:47:59,121
which use their energy
very conservatively,
640
00:47:59,156 --> 00:48:02,324
last for a long time,
don't glow too brightly.
641
00:48:02,359 --> 00:48:05,494
And those stars last
for a very long time.
642
00:48:05,529 --> 00:48:07,363
BULLOCK: So by measuring
the brightnesses
643
00:48:07,397 --> 00:48:10,399
and the colors of the stars
in a globular cluster,
644
00:48:10,434 --> 00:48:12,068
we can figure out
how old they are.
645
00:48:12,102 --> 00:48:13,469
And here's the remarkable thing.
646
00:48:13,503 --> 00:48:15,638
They're very old.
647
00:48:15,672 --> 00:48:18,841
Globular clusters, at least the stars
in globular clusters,
648
00:48:18,875 --> 00:48:23,179
in many cases are almost
as old as the universe itself.
649
00:48:27,317 --> 00:48:31,620
NARRATOR: Globular clusters
are living fossils.
650
00:48:31,655 --> 00:48:34,523
They're like discovering
a community of people
651
00:48:34,558 --> 00:48:37,893
who've been around
since the stone age.
652
00:48:40,764 --> 00:48:46,402
Some stars here have been shining
for 12 billion years--
653
00:48:46,436 --> 00:48:49,805
more than twice as long as the sun.
654
00:48:49,840 --> 00:48:54,710
And that's a helpful tool in placing
an age on the Milky Way.
655
00:48:56,813 --> 00:48:59,148
BULLOCK: Globular clusters
are part of our galaxy.
656
00:48:59,182 --> 00:49:00,282
They orbit our galaxy.
657
00:49:00,317 --> 00:49:03,352
In some sense they're tracers
of our galaxy itself.
658
00:49:03,386 --> 00:49:05,921
And so by the fact that
the globular clusters are so old,
659
00:49:05,956 --> 00:49:08,791
it suggests that the galaxy is old.
660
00:49:11,795 --> 00:49:15,131
NARRATOR: And our galaxy
isn't just old--
661
00:49:15,165 --> 00:49:18,834
it's very old.
662
00:49:18,869 --> 00:49:25,074
In fact, the Milky Way is one
of the oldest objects in the cosmos.
663
00:49:25,108 --> 00:49:29,712
It's been around almost since
the beginning of the entire universe--
664
00:49:29,746 --> 00:49:32,681
at least 12 billion years.
665
00:49:34,784 --> 00:49:40,222
Globular clusters also show
that the chemistry of the galaxy back then
666
00:49:40,257 --> 00:49:44,460
was very different
from how it is today.
667
00:49:46,863 --> 00:49:49,765
KIRSHNER: We can measure
the chemical properties of those stars.
668
00:49:49,799 --> 00:49:54,270
Turns out they have very low abundances
of the heavy elements.
669
00:49:54,304 --> 00:49:58,073
Things like iron are very rare
in globular cluster stars,
670
00:49:58,108 --> 00:50:00,709
compared to a star like the sun.
671
00:50:02,746 --> 00:50:08,384
NARRATOR: That means the early galaxy
was a far less colorful place.
672
00:50:12,389 --> 00:50:15,591
Without heavy elements
there weren't the beautiful hues
673
00:50:15,625 --> 00:50:20,462
we see in nebulas and
supernova remnants today.
674
00:50:20,497 --> 00:50:25,801
Even more importantly--
it was a galaxy without life.
675
00:50:27,537 --> 00:50:32,808
It took billions of years for stars
to form enough heavy elements
676
00:50:32,842 --> 00:50:37,880
for the evolution of life to begin
anywhere in the Milky Way...
677
00:50:42,652 --> 00:50:44,620
...leaving many to wonder
678
00:50:44,654 --> 00:50:49,191
how the galaxy has managed
to keep going for so long.
679
00:50:55,031 --> 00:50:57,566
BULLOCK: One of the puzzles
about our galaxy
680
00:50:57,601 --> 00:51:01,136
is that we know that it's had
stars forming continuously
681
00:51:01,171 --> 00:51:03,472
for about the last
ten billion years.
682
00:51:03,506 --> 00:51:06,175
But at the rate it's eating up
its gas now,
683
00:51:06,209 --> 00:51:08,844
it's forming new stars,
it should burn out that gas soon.
684
00:51:08,878 --> 00:51:10,179
It should run out of fuel.
685
00:51:10,213 --> 00:51:12,648
And so there has to be
some source for new fuel.
686
00:51:12,682 --> 00:51:16,752
NARRATOR: That source must be
outside the galaxy.
687
00:51:16,786 --> 00:51:22,458
And recently astronomers
made a startling discovery:
688
00:51:22,492 --> 00:51:27,463
Globular clusters aren't the only
groups of stars orbiting the Milky Way.
689
00:51:27,497 --> 00:51:31,767
There are other tiny galaxies
circling our galaxy
690
00:51:31,801 --> 00:51:35,638
called ultra faint dwarf galaxies.
691
00:51:35,672 --> 00:51:37,339
BULLOCK: The reason
why we haven't known
692
00:51:37,374 --> 00:51:39,642
about these dwarf galaxies
for very long,
693
00:51:39,676 --> 00:51:42,611
these so-called
ultra faint dwarf galaxies,
694
00:51:42,646 --> 00:51:45,214
is that they contain
just a few hundred stars,
695
00:51:45,248 --> 00:51:47,016
a thousand stars.
696
00:51:47,050 --> 00:51:50,319
So you try to find a clump
of a thousand stars
697
00:51:50,353 --> 00:51:52,755
while looking through a mass
of a billion stars.
698
00:51:52,789 --> 00:51:53,789
It's not easy.
699
00:51:53,823 --> 00:51:55,591
This is a needle
in a haystack problem.
700
00:51:55,625 --> 00:51:57,793
And it's only because
we have the precise maps,
701
00:51:57,827 --> 00:52:00,229
it's the precision
of modern astronomy
702
00:52:00,263 --> 00:52:01,697
that's allowed us to discover
703
00:52:01,731 --> 00:52:04,767
these extremely interesting
dwarf galaxies.
704
00:52:07,070 --> 00:52:10,806
NARRATOR: These elusive bodies
may help solve the mystery
705
00:52:10,840 --> 00:52:13,709
of what's fueling the galaxy.
706
00:52:15,312 --> 00:52:19,114
BULLOCK: So these dwarf galaxies
are whizzing around our galaxy.
707
00:52:19,149 --> 00:52:20,649
They're in orbit around it.
708
00:52:20,684 --> 00:52:22,618
Now sometimes they get too close,
709
00:52:22,652 --> 00:52:25,087
and when they get too close
they get ripped apart.
710
00:52:25,121 --> 00:52:29,925
In fact they get eaten,
in some sense, by our galaxy.
711
00:52:29,959 --> 00:52:34,563
NARRATOR: This computer model
shows dwarf galaxies as colored discs
712
00:52:34,597 --> 00:52:37,733
with our galaxy in the center.
713
00:52:37,767 --> 00:52:43,105
Over time, our galaxy
pulls dwarf galaxies in,
714
00:52:43,139 --> 00:52:46,742
devours them, and uses
their gas and dust
715
00:52:46,776 --> 00:52:50,746
to eventually form new stars.
716
00:52:53,116 --> 00:52:54,383
BULLOCK: So in much the same way
717
00:52:54,417 --> 00:52:57,486
that a large city might sort of
cannibalize its neighbors,
718
00:52:57,520 --> 00:53:02,424
the Milky Way is cannibalizing
its dwarf galaxy population.
719
00:53:02,459 --> 00:53:05,494
NARRATOR: Globular clusters
and dwarf galaxies
720
00:53:05,528 --> 00:53:10,299
provide crucial insight
to just how old our galaxy is...
721
00:53:10,333 --> 00:53:15,070
and how it's managed
to survive for so long.
722
00:53:15,105 --> 00:53:20,075
These bodies were once thought
to mark the Milky Way's city limits,
723
00:53:20,110 --> 00:53:24,813
the very outer reaches
of our star city.
724
00:53:24,848 --> 00:53:29,551
But today astronomers
are rethinking all that.
725
00:53:29,586 --> 00:53:34,423
Our galaxy might be bigger
than what we can see,
726
00:53:34,457 --> 00:53:39,461
spreading out further
than we ever imagined.
727
00:53:43,433 --> 00:53:45,100
We're picking up our Earth
728
00:53:45,135 --> 00:53:48,370
and moving from our quiet suburb
to a new neighborhood
729
00:53:48,405 --> 00:53:51,607
in the outer spiral arm
of our galaxy.
730
00:53:51,641 --> 00:53:53,942
Here we'll uncover the mystery
731
00:53:53,977 --> 00:53:59,047
of what holds all the stars
in the Milky Way together.
732
00:54:01,651 --> 00:54:06,121
From our new address, the night sky
looks a little different.
733
00:54:06,156 --> 00:54:11,126
The Milky Way is smaller
and the sky darker.
734
00:54:11,161 --> 00:54:17,466
Here, tens of thousands of light years
away from the center of our galaxy,
735
00:54:17,500 --> 00:54:21,870
we're still bound
by the force of gravity.
736
00:54:24,441 --> 00:54:26,575
BULLOCK: Gravity is the force
that makes any two objects
737
00:54:26,609 --> 00:54:28,277
want to move towards each other.
738
00:54:32,415 --> 00:54:38,821
NARRATOR: On Earth, cities are built
with iron girders and concrete beams--
739
00:54:38,855 --> 00:54:44,760
an invisible scaffold which holds
buildings up against the pull of gravity.
740
00:54:47,464 --> 00:54:54,036
Without this scaffolding, skyscrapers
would crumble and bridges collapse.
741
00:54:57,407 --> 00:55:02,511
Gravity governs Earth
and the entire universe.
742
00:55:10,286 --> 00:55:15,524
Anything that has mass
has a gravitational pull.
743
00:55:15,558 --> 00:55:19,361
The more the mass,
the stronger the pull.
744
00:55:21,664 --> 00:55:28,470
With 200 billion stars,
the Milky Way has a huge mass--
745
00:55:28,505 --> 00:55:32,975
and a tremendous
gravitational attraction to match.
746
00:55:33,009 --> 00:55:38,280
So, like a building, our galaxy
also needs propping up
747
00:55:38,314 --> 00:55:41,416
against the force of gravity.
748
00:55:43,786 --> 00:55:45,854
BULLOCK: Imagine the disc
of our galaxy.
749
00:55:45,889 --> 00:55:47,789
If you just took a disc of stars
750
00:55:47,824 --> 00:55:48,824
and put it there,
751
00:55:48,858 --> 00:55:50,359
gravity would tend to make
752
00:55:50,393 --> 00:55:52,194
this disc collapse in on itself,
753
00:55:52,228 --> 00:55:54,263
and it would immediately
just fall together.
754
00:55:54,297 --> 00:55:56,698
That's not what we see
with the galaxy.
755
00:55:56,733 --> 00:56:00,002
What's actually going on is the stars
are orbiting around the center,
756
00:56:00,036 --> 00:56:01,770
and that's what keeps them
from falling in,
757
00:56:01,804 --> 00:56:05,774
in much the same way that the Earth
is orbiting around the sun.
758
00:56:06,910 --> 00:56:11,847
NARRATOR: The planets in our solar system
are in a delicate balance--
759
00:56:11,881 --> 00:56:14,616
gravity pulls them towards the sun
760
00:56:14,651 --> 00:56:20,822
while their orbital velocity wants
to fling them out into space.
761
00:56:22,692 --> 00:56:24,793
In order to stay balanced,
762
00:56:24,827 --> 00:56:29,865
planets further from the sun
must orbit more slowly.
763
00:56:31,234 --> 00:56:33,001
BULLOCK: If you go
to more distant planets
764
00:56:33,036 --> 00:56:34,469
at the edge of the solar system,
765
00:56:34,504 --> 00:56:37,205
they're going around the sun
much more slowly than the Earth is,
766
00:56:37,240 --> 00:56:40,075
and that's because
the gravity is weaker.
767
00:56:40,109 --> 00:56:45,180
NARRATOR: The same should hold true
for stars in the Milky Way.
768
00:56:45,214 --> 00:56:49,818
They all orbit the center
of the galaxy,
769
00:56:49,852 --> 00:56:54,823
but the stars in the outer arm
should be traveling more slowly
770
00:56:54,857 --> 00:56:58,493
than those closer
to the galaxy's heart.
771
00:56:58,528 --> 00:57:00,796
BULLOCK: What's interesting
is that's not what's going on.
772
00:57:04,434 --> 00:57:06,501
The stars in the outer parts
of the galaxy
773
00:57:06,536 --> 00:57:10,739
are spinning around just as quickly
as those in the inner parts.
774
00:57:10,773 --> 00:57:13,775
NARRATOR: And they're not
the only ones.
775
00:57:13,810 --> 00:57:16,645
BULLOCK: It's not just our galaxy;
it's every galaxy we look at.
776
00:57:16,679 --> 00:57:23,118
Every galaxy we look at seems to be
spinning too fast in its outer parts.
777
00:57:23,152 --> 00:57:24,519
NARRATOR: These speeding stars
778
00:57:24,554 --> 00:57:28,290
should be flung out
of the galaxy altogether.
779
00:57:28,324 --> 00:57:31,627
But they're not.
780
00:57:31,661 --> 00:57:34,229
BULLOCK: That is a puzzle.
781
00:57:34,263 --> 00:57:36,565
This means that there's
a lot more mass there
782
00:57:36,599 --> 00:57:38,533
that we just can't see.
783
00:57:40,603 --> 00:57:42,871
NARRATOR: Mass that produces
the gravity
784
00:57:42,905 --> 00:57:47,075
that holds these stars
in their orbits.
785
00:57:49,679 --> 00:57:52,614
But when astronomers
look for the mass,
786
00:57:52,649 --> 00:57:57,219
there appears to be
nothing there...
787
00:57:57,253 --> 00:58:04,760
leading cosmologists like Joel Primack
to an astounding conclusion.
788
00:58:04,794 --> 00:58:06,762
JOEL PRIMACK: All of the galaxies,
789
00:58:06,796 --> 00:58:10,265
all of the stars and gas and dust
and planets and everything else
790
00:58:10,299 --> 00:58:13,635
that we can see with
our greatest telescopes,
791
00:58:13,670 --> 00:58:18,940
represent about half of one percent
of what's actually out there.
792
00:58:18,975 --> 00:58:20,709
The rest is invisible.
793
00:58:20,743 --> 00:58:25,514
It's mostly some mysterious substance
that we call dark matter.
794
00:58:25,548 --> 00:58:27,749
BULLOCK: You can't see dark matter.
795
00:58:27,784 --> 00:58:30,252
The reason why you
can see normal matter
796
00:58:30,286 --> 00:58:33,488
is because light shines on it
and reflects off of it.
797
00:58:33,523 --> 00:58:35,223
That's how you can see me.
798
00:58:35,258 --> 00:58:36,391
Dark matter doesn't work that way.
799
00:58:36,426 --> 00:58:39,695
The light goes right through
the dark matter.
800
00:58:39,729 --> 00:58:43,632
The way we detect dark matter
is because it has mass.
801
00:58:43,666 --> 00:58:47,402
Anything with mass affects
other things via gravity.
802
00:58:47,437 --> 00:58:49,838
That's the golden rule of mass,
that's what mass does,
803
00:58:49,872 --> 00:58:54,042
it tugs on other things
because of gravity.
804
00:58:54,077 --> 00:58:59,881
NARRATOR: Without dark matter,
the Milky Way couldn't exist.
805
00:58:59,916 --> 00:59:01,383
BULLOCK: So the galaxy is spinning.
806
00:59:01,417 --> 00:59:04,820
The galaxy is spinning fairly rapidly.
807
00:59:04,854 --> 00:59:08,557
The reason why it can spin so rapidly
is because it has so much dark matter.
808
00:59:08,591 --> 00:59:12,761
The dark matter has a lot of mass
and therefore it has a lot of gravity,
809
00:59:12,795 --> 00:59:16,898
and that's what keeps the stars
whizzing around.
810
00:59:16,933 --> 00:59:19,101
If you were to magically take
all of the dark matter
811
00:59:19,135 --> 00:59:20,502
away from our galaxy,
812
00:59:20,536 --> 00:59:21,536
it would fly apart.
813
00:59:21,571 --> 00:59:23,171
The stars would just
keep going straight
814
00:59:23,206 --> 00:59:26,541
and in a very short amount of time
the galaxy would just be gone.
815
00:59:26,576 --> 00:59:31,079
PRIMACK: There'd be just a mess
of stuff flying every which way.
816
00:59:31,114 --> 00:59:32,814
And that's not just true
of our galaxy,
817
00:59:32,849 --> 00:59:34,082
it's true of every galaxy
818
00:59:34,117 --> 00:59:36,852
and every cluster of galaxies
in the universe.
819
00:59:36,886 --> 00:59:40,922
They're all held together
by this invisible stuff
820
00:59:40,957 --> 00:59:43,325
that we call dark matter.
821
00:59:43,359 --> 00:59:46,862
BULLOCK: So we need the dark matter.
822
00:59:46,896 --> 00:59:49,798
It's the glue that holds
galaxies together.
823
00:59:52,468 --> 00:59:54,569
NARRATOR: The discovery
of dark matter
824
00:59:54,604 --> 00:59:59,307
has revolutionized our picture
of the Milky Way.
825
00:59:59,342 --> 01:00:05,580
The stars of the galaxy represent
just a fraction of its mass.
826
01:00:05,615 --> 01:00:11,386
The rest is made up of an invisible halo
of dark matter--
827
01:00:11,420 --> 01:00:17,726
surrounding every single star
and every creature in the galaxy.
828
01:00:20,329 --> 01:00:23,064
PRIMACK: The stars are
just the central region.
829
01:00:23,099 --> 01:00:25,934
The halo is at least ten times bigger
830
01:00:25,968 --> 01:00:29,437
and weighs much more
than ten times more
831
01:00:29,472 --> 01:00:33,341
than all the stars and gas and dust
that we can see.
832
01:00:33,376 --> 01:00:38,713
It's that whole structure
that's the real Milky Way galaxy.
833
01:00:38,748 --> 01:00:40,315
And that's not just true
of our galaxy,
834
01:00:40,349 --> 01:00:43,351
it's true of every galaxy
we've ever studied.
835
01:00:45,721 --> 01:00:51,960
NARRATOR: But dark matter does more
than simply hold galaxies together.
836
01:00:51,994 --> 01:00:55,497
Astronomers now think
it binds the Milky Way
837
01:00:55,531 --> 01:01:02,804
into an extraordinary structure
with billions of other galaxies--
838
01:01:02,839 --> 01:01:08,410
a structure that reaches
to the very edge of the universe.
839
01:01:14,383 --> 01:01:17,219
We've left our home galaxy
to take the earth
840
01:01:17,253 --> 01:01:22,157
across billions of light years
of space and time.
841
01:01:27,563 --> 01:01:28,763
BULLOCK: One of the great things
about telescopes
842
01:01:28,798 --> 01:01:31,399
is they're time machines.
843
01:01:31,434 --> 01:01:33,869
Because light travels at a finite speed,
844
01:01:33,903 --> 01:01:35,503
when we look at distant objects
845
01:01:35,538 --> 01:01:39,507
we see them as they were
when the light left them.
846
01:01:39,542 --> 01:01:43,345
NARRATOR: As astronomers look back
over billions of years,
847
01:01:43,379 --> 01:01:47,148
they see a universe
teeming with galaxies.
848
01:01:50,453 --> 01:01:55,757
But these galaxies aren't scattered
randomly through space.
849
01:01:58,261 --> 01:02:07,035
They cluster along delicate filaments
woven in an intricate structure--
850
01:02:07,069 --> 01:02:10,105
a vast cosmic web
that holds the answer
851
01:02:10,139 --> 01:02:14,109
to the birth of galaxies
themselves.
852
01:02:18,614 --> 01:02:23,084
It's a story shrouded
in darkness.
853
01:02:23,119 --> 01:02:30,992
Look back far enough and gradually
all the galaxies disappear.
854
01:02:31,027 --> 01:02:34,496
We've reached a mysterious
period of time,
855
01:02:34,530 --> 01:02:38,333
12.5 billion years ago.
856
01:02:38,367 --> 01:02:40,669
BULLOCK: There's this time period
that we can't see
857
01:02:40,703 --> 01:02:42,370
because nothing's formed yet.
858
01:02:42,405 --> 01:02:46,141
It's this epoch that's called
the dark ages.
859
01:02:49,078 --> 01:02:53,114
NARRATOR: During the dark ages,
the universe was a very different place
860
01:02:53,149 --> 01:02:56,084
than the one we live in today.
861
01:02:58,688 --> 01:03:02,724
It's filled with dense clouds
of hydrogen gas.
862
01:03:04,994 --> 01:03:08,897
Just as gas obscures stars
in the Milky Way today,
863
01:03:08,931 --> 01:03:15,403
these clouds of hydrogen block the view
inside the early universe.
864
01:03:15,438 --> 01:03:18,540
BULLOCK: It's extremely frustrating
because this region,
865
01:03:18,574 --> 01:03:22,043
this time period, holds within it,
in some sense,
866
01:03:22,078 --> 01:03:25,714
the Rosetta Stone
of galaxy formation.
867
01:03:25,748 --> 01:03:28,283
NARRATOR: But there is one clue
to what's happening
868
01:03:28,317 --> 01:03:33,121
inside those dense
hydrogen clouds.
869
01:03:33,155 --> 01:03:34,990
Look back further in time
870
01:03:35,024 --> 01:03:40,829
to a moment just 380,000 years
after the big bang.
871
01:03:40,863 --> 01:03:44,199
The universe isn't filled
with darkness...
872
01:03:47,536 --> 01:03:50,438
but with light.
873
01:03:50,473 --> 01:03:55,343
Its faint afterglow is still visible
to astronomers today.
874
01:03:57,813 --> 01:03:59,014
BULLOCK: In fact,
this picture is amazing.
875
01:03:59,048 --> 01:04:01,416
This is a picture
of the early universe.
876
01:04:01,450 --> 01:04:06,521
This is an image of the afterglow
of the big bang.
877
01:04:06,555 --> 01:04:10,191
NARRATOR: The universe is filled
with a hot atmosphere
878
01:04:10,226 --> 01:04:13,028
of matter and radiation.
879
01:04:15,464 --> 01:04:19,968
But already the seeds of change
are being sown.
880
01:04:24,740 --> 01:04:26,441
BULLOCK: Everywhere we look
around us in the universe
881
01:04:26,475 --> 01:04:29,844
we see structure; we see galaxies
all over the place.
882
01:04:29,879 --> 01:04:31,713
Where do these galaxies
come from?
883
01:04:31,747 --> 01:04:34,816
There's a big clue to this
buried in this picture.
884
01:04:34,850 --> 01:04:36,484
If you look closely,
you can see
885
01:04:36,519 --> 01:04:39,320
that there are red spots
and there are blue spots.
886
01:04:39,355 --> 01:04:43,458
These red regions are regions
where there's basically more stuff,
887
01:04:43,492 --> 01:04:48,096
and the blue regions are the regions
where there's less stuff.
888
01:04:48,130 --> 01:04:50,899
NARRATOR: This image reveals
tiny variations
889
01:04:50,933 --> 01:04:55,637
in the density of the gas
that fills the early universe.
890
01:04:58,107 --> 01:05:02,143
Minute ripples
that will grow with time.
891
01:05:04,380 --> 01:05:07,882
BULLOCK: We think that these ripples,
these primordial ripples,
892
01:05:07,917 --> 01:05:10,785
are the seeds
to all future structure.
893
01:05:10,820 --> 01:05:15,090
These ripples eventually grew
into what became the first galaxies.
894
01:05:15,124 --> 01:05:17,058
NARRATOR: It takes
a powerful force
895
01:05:17,093 --> 01:05:21,529
to grow something so small
into something so big.
896
01:05:21,564 --> 01:05:24,365
BULLOCK: It's gravity
that amplifies these ripples,
897
01:05:24,400 --> 01:05:28,536
and in fact we need
an additional source of gravity
898
01:05:28,571 --> 01:05:32,240
to amplify those ripples to form
galaxies like we see today,
899
01:05:32,274 --> 01:05:35,677
and that additional gravity comes
in the form of dark matter.
900
01:05:38,848 --> 01:05:43,184
PRIMACK: What happens is that first
the dark matter forms the structure.
901
01:05:43,219 --> 01:05:46,554
The ordinary matter
then follows the dark matter.
902
01:05:46,589 --> 01:05:49,591
The ordinary matter is hydrogen
and helium at this stage.
903
01:05:49,625 --> 01:05:53,595
And the hydrogen and helium
fall to the center
904
01:05:53,629 --> 01:05:56,264
of the dark matter halos
that are forming,
905
01:05:56,298 --> 01:06:00,502
and that's going to become
the galaxies.
906
01:06:00,536 --> 01:06:02,770
NARRATOR: Dark matter may be
the missing link
907
01:06:02,805 --> 01:06:06,674
between these minute ripples
in the early universe
908
01:06:06,709 --> 01:06:11,479
and the vast cosmic web
that now fills space.
909
01:06:17,086 --> 01:06:20,955
But dark matter is invisible.
910
01:06:22,191 --> 01:06:27,428
So there's no way to actually see it
creating the cosmic web.
911
01:06:29,498 --> 01:06:31,633
But the process can be simulated
912
01:06:31,667 --> 01:06:36,137
in one of the world's
most powerful super computers.
913
01:06:39,441 --> 01:06:42,877
PRIMACK: Here we are at NASA Ames,
914
01:06:42,912 --> 01:06:48,650
the research center where we have
the Pleiades super computer.
915
01:06:48,684 --> 01:06:54,055
Each one of these cabinets
contains 512 processors.
916
01:06:54,089 --> 01:06:57,692
Let me show you.
917
01:06:57,726 --> 01:07:01,663
So that's half a terabyte
in each one of these cabinets.
918
01:07:01,697 --> 01:07:03,731
There's 110 of these cabinets
919
01:07:03,766 --> 01:07:07,702
to make up the entire
Pleiades super computer.
920
01:07:07,736 --> 01:07:09,904
So this is a really big
super computer.
921
01:07:09,939 --> 01:07:12,006
This is NASA's biggest.
922
01:07:14,210 --> 01:07:16,311
NARRATOR: The challenge
is equally big--
923
01:07:16,345 --> 01:07:18,780
to develop a virtual universe--
924
01:07:18,814 --> 01:07:22,884
from its early beginnings
all the way to the present day--
925
01:07:22,918 --> 01:07:30,024
to see what role dark matter might
have played in shaping the cosmos.
926
01:07:30,059 --> 01:07:33,328
If you tried to do this
on a home computer,
927
01:07:33,362 --> 01:07:36,598
it would take over 680 years.
928
01:07:38,467 --> 01:07:40,201
PRIMACK: If we're doing
our job right,
929
01:07:40,236 --> 01:07:44,239
we can put the pictures
into a video, if you like,
930
01:07:44,273 --> 01:07:48,009
that shows the whole structure
of the universe.
931
01:07:48,043 --> 01:07:51,079
NARRATOR: And this is the end result.
932
01:07:51,113 --> 01:07:53,248
It's called Bolshoi--
933
01:07:53,282 --> 01:07:55,817
an amazing visualization
934
01:07:55,851 --> 01:07:58,886
of what the structure
of dark matter might look like
935
01:07:58,921 --> 01:08:01,356
in the universe today.
936
01:08:05,194 --> 01:08:06,694
PRIMACK: So what we're looking at
937
01:08:06,729 --> 01:08:12,233
is a region about 200 million
light years across,
938
01:08:12,268 --> 01:08:15,737
which is actually just a small part
of our really big simulation
939
01:08:15,771 --> 01:08:18,906
that we call Bolshoi,
which is Russian for "big."
940
01:08:18,941 --> 01:08:22,343
Everything that you see here
is actually completely invisible.
941
01:08:22,378 --> 01:08:26,314
It's not the visible universe
that you're seeing.
942
01:08:26,348 --> 01:08:29,651
The bright spots are dark matter.
943
01:08:29,685 --> 01:08:35,757
They're the halos of dark matter
within which galaxies form.
944
01:08:35,791 --> 01:08:41,062
And each one of these little blobs
would represent probably one,
945
01:08:41,096 --> 01:08:45,233
or at most a couple
of Milky Way size galaxies.
946
01:08:45,267 --> 01:08:51,572
And you can see that the galaxies
are in long chains,
947
01:08:51,607 --> 01:08:53,875
filaments we call them.
948
01:08:53,909 --> 01:09:00,381
Basically all the structure is forming
along these filaments of dark matter.
949
01:09:03,118 --> 01:09:06,354
NARRATOR: Now comes
the real test of success:
950
01:09:06,388 --> 01:09:09,691
Primack compares
the Bolshoi predictions
951
01:09:09,725 --> 01:09:15,730
with the actual structure of galaxies
scientists see in the universe.
952
01:09:15,764 --> 01:09:17,398
PRIMACK: As far as we can tell,
953
01:09:17,433 --> 01:09:20,935
these simulated universes
that we make in the super computers
954
01:09:20,969 --> 01:09:23,271
look just like the observed universe.
955
01:09:23,305 --> 01:09:25,673
There don't seem to be
any discrepancies at all.
956
01:09:25,708 --> 01:09:29,110
This is exactly the way
we see the galaxies distributed
957
01:09:29,144 --> 01:09:32,914
in the observed universe.
958
01:09:32,948 --> 01:09:37,785
NARRATOR: The Bolshoi simulations
are astounding.
959
01:09:37,820 --> 01:09:43,691
They match the pattern of galaxies
seen in the cosmos today perfectly.
960
01:09:46,862 --> 01:09:48,496
It's persuasive evidence
961
01:09:48,530 --> 01:09:54,602
that dark matter has been sculpting
the universe for billions of years.
962
01:09:58,841 --> 01:10:00,575
PRIMACK: No, I'm really
impressed with this
963
01:10:00,609 --> 01:10:02,510
because we stuck
our necks way out
964
01:10:02,544 --> 01:10:05,680
when we made
these first predictions,
965
01:10:05,714 --> 01:10:08,349
and they turned out to be right.
966
01:10:08,384 --> 01:10:10,752
And they keep turning out
to be right.
967
01:10:10,786 --> 01:10:14,522
And, you know, this is, of course,
great joy for a theorist.
968
01:10:16,692 --> 01:10:20,194
NARRATOR: By going back
to the beginning of the universe,
969
01:10:20,229 --> 01:10:22,764
astronomers
have uncovered the origin
970
01:10:22,798 --> 01:10:28,369
of the underlying structure
of the entire cosmos.
971
01:10:28,404 --> 01:10:32,540
But our time travel
is far from over.
972
01:10:32,574 --> 01:10:39,647
The question of how the first galaxies
kindled the very first stars still remains.
973
01:10:43,185 --> 01:10:48,956
We're taking the earth
inside the dark age--
974
01:10:48,991 --> 01:10:53,094
a time over 12.5 billion years ago.
975
01:10:53,128 --> 01:10:57,598
The sight is spectacular.
976
01:10:57,633 --> 01:11:02,737
Our skies are lit by the first stars
of the Milky Way.
977
01:11:05,340 --> 01:11:09,243
Their light pierces the hydrogen fog--
978
01:11:09,278 --> 01:11:14,348
bathing the earth in strong
ultraviolet energy.
979
01:11:14,383 --> 01:11:21,556
These first stars will change the way
we see the universe forever.
980
01:11:21,590 --> 01:11:26,027
Tom Abel studies the life and death
of these early stars.
981
01:11:28,897 --> 01:11:31,866
TOM ABEL: The beautiful thing
is that we now have computers.
982
01:11:31,900 --> 01:11:34,435
We program them
with the laws of physics,
983
01:11:34,470 --> 01:11:36,571
put in some gravity,
hydrodynamics,
984
01:11:36,605 --> 01:11:39,240
how gases move around,
some of the chemistry,
985
01:11:39,274 --> 01:11:42,009
and as we evolve it
all together,
986
01:11:42,044 --> 01:11:45,213
we gain an intuition
of how stars come about,
987
01:11:45,247 --> 01:11:50,418
and in the case of the very first stars,
this is absolutely crucial.
988
01:11:53,088 --> 01:11:55,389
NARRATOR: Abel begins
with the basic ingredients
989
01:11:55,424 --> 01:11:58,926
available during the dark ages:
990
01:11:58,961 --> 01:12:03,831
hydrogen, helium,
dark matter and gravity.
991
01:12:05,834 --> 01:12:07,768
Using computer models,
992
01:12:07,803 --> 01:12:12,306
Abel recreates the lives
of these early stars.
993
01:12:17,546 --> 01:12:20,348
ABEL: Here we see one of
the first stars in the universe.
994
01:12:20,382 --> 01:12:22,650
It's a hundred times
as massive as the sun,
995
01:12:22,684 --> 01:12:26,153
a million times as bright.
996
01:12:26,188 --> 01:12:29,891
NARRATOR: The first stars are huge--
997
01:12:29,925 --> 01:12:33,361
swollen by the massive amounts
of hydrogen gas
998
01:12:33,395 --> 01:12:38,499
pulled in by the gravitational force
of dark matter.
999
01:12:38,534 --> 01:12:40,668
ABEL: And so even though
they have all this fuel to burn
1000
01:12:40,702 --> 01:12:42,470
you'd think they could live
for a long time.
1001
01:12:42,504 --> 01:12:44,839
They run through it so quickly
1002
01:12:44,873 --> 01:12:50,778
that even after a few million years
they're already dead.
1003
01:12:50,812 --> 01:12:52,813
NARRATOR: The first stars
in our Milky Way
1004
01:12:52,848 --> 01:12:56,150
are fierce, high octane stars--
1005
01:12:56,184 --> 01:13:00,521
burning their hydrogen fuel
at tremendous rates--
1006
01:13:00,556 --> 01:13:04,125
racing through their life cycle.
1007
01:13:04,159 --> 01:13:05,593
ABEL: They're like the rock stars.
1008
01:13:05,627 --> 01:13:07,261
They live fast and die young.
1009
01:13:07,296 --> 01:13:09,130
They run through
their fuel very quickly
1010
01:13:09,164 --> 01:13:13,234
and even afterjust a few million years
they already die.
1011
01:13:13,268 --> 01:13:16,504
NARRATOR: They die in some
of the most violent explosions
1012
01:13:16,538 --> 01:13:20,408
ever to rock the universe--
1013
01:13:20,442 --> 01:13:24,278
gigantic supernovas
that shine brilliantly.
1014
01:13:28,350 --> 01:13:29,717
The energy given off
1015
01:13:29,751 --> 01:13:33,187
during the life and death
of these massive stars
1016
01:13:33,221 --> 01:13:36,891
leads to a miraculous transformation.
1017
01:13:40,495 --> 01:13:43,564
ABEL: In the first billion years
of the universe's history,
1018
01:13:43,599 --> 01:13:47,702
galaxies start to form
in a dark hydrogen fog,
1019
01:13:47,736 --> 01:13:51,105
their light not being able
to get to us.
1020
01:13:51,139 --> 01:13:52,673
But as time progresses
1021
01:13:52,708 --> 01:13:56,644
and their most massive stars
put out ultraviolet radiation,
1022
01:13:56,678 --> 01:14:00,381
it's that radiation itself
that changes the fog around them,
1023
01:14:00,415 --> 01:14:03,217
and the universe becomes
transparent in those regions.
1024
01:14:03,251 --> 01:14:08,489
These galaxies in here are clearing out
the fog around them.
1025
01:14:08,523 --> 01:14:12,393
NARRATOR: The blue voids
are where energy from the new stars
1026
01:14:12,427 --> 01:14:16,030
is clearing the dark hydrogen fog.
1027
01:14:20,902 --> 01:14:23,471
ABEL: But towards a billion years
after the big bang
1028
01:14:23,505 --> 01:14:25,206
the entire fog has cleared
1029
01:14:25,240 --> 01:14:28,342
and we now see all the galaxies,
1030
01:14:28,377 --> 01:14:31,312
and the dark ages end.
1031
01:14:34,116 --> 01:14:36,417
NARRATOR: As the hydrogen fog lifts,
1032
01:14:36,451 --> 01:14:42,189
we get our first glimpse
of newborn galaxies...
1033
01:14:42,224 --> 01:14:46,727
including our very own Milky Way.
1034
01:15:01,276 --> 01:15:04,445
RICHARD ELLIS: This remarkable image
is the Hubble ultra deep field.
1035
01:15:04,479 --> 01:15:07,014
It's the longest exposure
that's ever been taken
1036
01:15:07,049 --> 01:15:08,816
with the Hubble Space Telescope.
1037
01:15:08,850 --> 01:15:10,451
It's a truly remarkable image,
1038
01:15:10,485 --> 01:15:15,022
probably the most famous
to professional astronomers.
1039
01:15:15,057 --> 01:15:20,461
NARRATOR: For over eleven days
Hubble pointed at a tiny patch of sky
1040
01:15:20,495 --> 01:15:24,799
about the width of a dime
held 75 feet away.
1041
01:15:29,037 --> 01:15:32,873
Every faint smudge of light is a galaxy.
1042
01:15:36,778 --> 01:15:40,481
For Richard Ellis,
it's a treasure trove.
1043
01:15:41,917 --> 01:15:44,985
ELLIS: So much like an archaeologist
would piece together history
1044
01:15:45,020 --> 01:15:47,855
by digging into deeper
and deeper layers,
1045
01:15:47,889 --> 01:15:51,192
so a cosmologist like myself
uses this image
1046
01:15:51,226 --> 01:15:52,993
to look at the history of the universe,
1047
01:15:53,028 --> 01:15:56,864
how the most distant galaxies,
seen as they were a long time ago,
1048
01:15:56,898 --> 01:16:02,436
evolve and grow to the bigger systems
that we see around us today.
1049
01:16:02,471 --> 01:16:08,476
NARRATOR: This image gives us
a sense of the dawn of our Milky Way.
1050
01:16:08,510 --> 01:16:10,711
ELLIS: When we look
at these early galaxies,
1051
01:16:10,746 --> 01:16:14,782
they don't resemble the star cities
that we see today.
1052
01:16:14,816 --> 01:16:16,650
They're lumpy, they're irregular,
1053
01:16:16,685 --> 01:16:19,620
they appear to be interacting
with their neighbors,
1054
01:16:19,654 --> 01:16:21,589
they're physically very, very small.
1055
01:16:21,623 --> 01:16:26,594
So clearly the universe was
very different in those early times.
1056
01:16:26,628 --> 01:16:32,399
NARRATOR: 12 billion years ago
the universe is a much smaller place.
1057
01:16:32,434 --> 01:16:36,270
It hasn't yet expanded
to the size it is today.
1058
01:16:38,840 --> 01:16:44,345
Our young Milky Way
is jostling for room.
1059
01:16:44,379 --> 01:16:46,514
ELLIS: So it's very difficult
for these early galaxies
1060
01:16:46,548 --> 01:16:48,349
to establish themselves.
1061
01:16:48,383 --> 01:16:54,922
These early galaxies are struggling
to survive at this very early time.
1062
01:16:56,191 --> 01:16:59,460
NARRATOR: It's survival of the fittest--
1063
01:16:59,494 --> 01:17:04,598
the largest galaxies grow bigger
by devouring the smallest.
1064
01:17:06,802 --> 01:17:08,836
ELLIS: So it's tough
for these early systems to form,
1065
01:17:08,870 --> 01:17:12,339
but clearly they do, and they eventually
merge with their neighbors
1066
01:17:12,374 --> 01:17:15,209
and form the bigger systems
that we see today.
1067
01:17:18,680 --> 01:17:20,815
NARRATOR: These collisions
in the early universe
1068
01:17:20,849 --> 01:17:26,320
created the beautiful spiral galaxy
we live in today...
1069
01:17:28,790 --> 01:17:31,325
...and they've never stopped.
1070
01:17:31,359 --> 01:17:34,228
Astronomers believe
there's still one final collision
1071
01:17:34,262 --> 01:17:37,198
in store for the Milky Way.
1072
01:17:37,232 --> 01:17:40,868
One that will change it forever.
1073
01:17:53,748 --> 01:18:00,521
We've transported the earth
three billion years into the future.
1074
01:18:00,555 --> 01:18:06,393
The sky is dominated by
a massive galaxy called Andromeda.
1075
01:18:08,964 --> 01:18:12,132
The view may look peaceful,
1076
01:18:12,167 --> 01:18:14,969
but one of the greatest calamities
in the universe
1077
01:18:15,003 --> 01:18:17,238
is about to take place...
1078
01:18:19,574 --> 01:18:25,579
...and clues to the impending disaster
lie in these mysterious Hubble images.
1079
01:18:27,349 --> 01:18:31,685
Galaxies unlike any other...
1080
01:18:31,720 --> 01:18:33,487
distorted...
1081
01:18:35,824 --> 01:18:38,993
deformed.
1082
01:18:39,027 --> 01:18:41,929
Astronomers rely
on computers for help
1083
01:18:41,963 --> 01:18:46,467
in decoding what these
mysterious objects represent.
1084
01:18:48,536 --> 01:18:51,906
PRIMACK: What we do is
we make galaxies
1085
01:18:51,940 --> 01:18:55,876
that look just like the Milky Way
and similar galaxies.
1086
01:18:55,911 --> 01:18:58,979
And we let them evolve
in the computer,
1087
01:18:59,014 --> 01:19:01,115
they develop
the spiral structure,
1088
01:19:01,149 --> 01:19:03,651
they look quite realistic.
1089
01:19:03,685 --> 01:19:09,590
We then put them
on a collision path.
1090
01:19:09,624 --> 01:19:11,959
NARRATOR: Freeze frame
these simulations
1091
01:19:11,993 --> 01:19:14,028
and match them with real images
1092
01:19:14,062 --> 01:19:19,633
and suddenly the picture
becomes clear:
1093
01:19:19,668 --> 01:19:25,506
It's the greatest clash
in the cosmos--
1094
01:19:25,540 --> 01:19:28,409
galaxies in collision.
1095
01:19:32,948 --> 01:19:37,184
Like cities, galaxies
tend to cluster.
1096
01:19:37,218 --> 01:19:39,486
Our Milky Way
belongs to a cluster
1097
01:19:39,521 --> 01:19:41,989
called the local group,
1098
01:19:42,023 --> 01:19:45,826
made up of at least 50 galaxies.
1099
01:19:49,331 --> 01:19:52,499
The largest in the pack
is Andromeda--
1100
01:19:52,534 --> 01:19:56,270
a spiral galaxy that's
even bigger than ours.
1101
01:19:58,340 --> 01:20:04,278
Today Andromeda lies
2.5 million light years away.
1102
01:20:04,312 --> 01:20:11,552
But astronomers like Abraham Loeb
believe that distance is closing in.
1103
01:20:11,586 --> 01:20:13,821
ABRAHAM LOEB: When I started
working in astrophysics
1104
01:20:13,855 --> 01:20:15,990
I noticed that most
of my colleagues
1105
01:20:16,024 --> 01:20:19,893
are thinking about other galaxies
interacting with each other,
1106
01:20:19,928 --> 01:20:22,062
colliding with each other,
1107
01:20:22,097 --> 01:20:25,265
and I was wondering why
aren't they examining
1108
01:20:25,300 --> 01:20:29,203
the future of the Milky Way
and the Andromeda Galaxy
1109
01:20:29,237 --> 01:20:32,773
as they will come together.
1110
01:20:32,807 --> 01:20:35,776
NARRATOR: Trouble is brewing
for our star city.
1111
01:20:37,812 --> 01:20:42,249
PRIMACK: Our galaxy is rushing
toward the great galaxy Andromeda,
1112
01:20:42,283 --> 01:20:43,884
they're rushing toward each other,
1113
01:20:43,918 --> 01:20:46,286
and they're going
to encounter each other
1114
01:20:46,321 --> 01:20:49,123
in a couple billion years.
1115
01:20:52,327 --> 01:20:53,927
NARRATOR: Loeb and his colleagues
1116
01:20:53,962 --> 01:20:58,699
decide to simulate this
intergalactic clash of the titans.
1117
01:21:00,668 --> 01:21:05,239
LOEB: This was the first
simulation of its kind.
1118
01:21:05,273 --> 01:21:08,575
Initially the two galaxies
plunge through each other
1119
01:21:08,610 --> 01:21:14,982
producing these beautiful tails of stars,
due to the force of gravity.
1120
01:21:15,016 --> 01:21:18,385
They run away, turn around
and come back together,
1121
01:21:18,420 --> 01:21:20,921
to make one big
spheroid of stars,
1122
01:21:20,955 --> 01:21:24,758
which I called
the Milkomeda Galaxy.
1123
01:21:24,793 --> 01:21:28,195
NARRATOR: When the Milky Way
merges with Andromeda,
1124
01:21:28,229 --> 01:21:32,332
almost one trillion stars
will come together.
1125
01:21:38,239 --> 01:21:39,606
KIRSHNER: The beautiful
spiral structure
1126
01:21:39,641 --> 01:21:41,108
of our Milky Way galaxy
1127
01:21:41,142 --> 01:21:43,277
is not something that's
going to last forever.
1128
01:21:43,311 --> 01:21:47,314
It's going to be a mess,
for a while.
1129
01:21:47,348 --> 01:21:49,383
The collision will not be one
1130
01:21:49,417 --> 01:21:51,418
in which these two things
are destroyed,
1131
01:21:51,453 --> 01:21:54,488
but it is one where the gas
in each system
1132
01:21:54,522 --> 01:21:57,091
will collide with the gas
in the other.
1133
01:21:57,125 --> 01:22:00,794
That it'll have a burst
of star formation.
1134
01:22:00,829 --> 01:22:03,497
LOEB: And the formation
of these new stars
1135
01:22:03,531 --> 01:22:07,968
will mark the rebirth
of a new galaxy.
1136
01:22:12,340 --> 01:22:14,775
NARRATOR: This spectacular
Hubble image
1137
01:22:14,809 --> 01:22:18,512
shows the Antennae Galaxies--
1138
01:22:18,546 --> 01:22:25,652
a grand cosmic collision
between two spiral star cities.
1139
01:22:25,687 --> 01:22:30,424
The galaxies are
in a frenzy of star birth--
1140
01:22:30,458 --> 01:22:36,697
a multitude of nebulas
glow pink in the darkness--
1141
01:22:36,731 --> 01:22:39,833
one final flare of stellar activity
1142
01:22:39,868 --> 01:22:43,504
before the galaxies merge
to become one.
1143
01:22:45,173 --> 01:22:48,709
This is the fate that awaits
our Milky Way
1144
01:22:48,743 --> 01:22:54,014
when it merges with Andromeda
three billion years from now.
1145
01:22:56,584 --> 01:22:57,851
KIRSHNER: When they collide
1146
01:22:57,886 --> 01:23:01,221
there will be a lot of new
star formation that takes place,
1147
01:23:01,256 --> 01:23:05,559
there will be a kind of rejuvenation
of the Milky Way for a little while
1148
01:23:05,593 --> 01:23:08,262
and then eventually
this combined system
1149
01:23:08,296 --> 01:23:10,597
will settle down
to become a new thing,
1150
01:23:10,632 --> 01:23:12,332
probably a bigger galaxy
1151
01:23:12,367 --> 01:23:16,837
than either of the galaxies
out of which it was made.
1152
01:23:16,871 --> 01:23:23,510
NARRATOR: But the real surprise
is the shape of this new galaxy.
1153
01:23:23,545 --> 01:23:25,345
PRIMACK: A new galaxy is formed
1154
01:23:25,380 --> 01:23:29,650
where instead of the discs
that the original galaxies had,
1155
01:23:29,684 --> 01:23:33,053
where all the stars are going around
more or less on a plane,
1156
01:23:33,087 --> 01:23:36,023
instead the stars are going
every which way,
1157
01:23:36,057 --> 01:23:40,661
just like the elliptical galaxies
that we see.
1158
01:23:40,695 --> 01:23:43,263
And so we're pretty sure
that this process
1159
01:23:43,298 --> 01:23:48,702
must be a large part
of how elliptical galaxies form.
1160
01:23:48,736 --> 01:23:51,205
NARRATOR: The collision
of the Milky Way with Andromeda
1161
01:23:51,239 --> 01:23:55,309
will leave behind
a giant elliptical galaxy.
1162
01:23:59,347 --> 01:24:04,151
But before that happens
there'll be one final sight to behold.
1163
01:24:05,687 --> 01:24:08,689
LOEB: The image of Andromeda
will be stretched across the sky,
1164
01:24:08,723 --> 01:24:14,061
looming as big
as the Milky Way itself,
1165
01:24:14,095 --> 01:24:19,032
and it's conceivable that there
would be human beings like ourselves
1166
01:24:19,067 --> 01:24:24,104
looking at the sky and seeing
this spectacular image.
1167
01:24:24,138 --> 01:24:28,909
NARRATOR: We might not be
the only beings enjoying the view.
1168
01:24:28,943 --> 01:24:33,780
Could our galaxy be home
to other civilizations?
1169
01:24:33,815 --> 01:24:39,386
Unknown life yet to be discovered
inside the Milky Way?
1170
01:24:49,664 --> 01:24:55,669
There are around 200 billion stars
in our galaxy.
1171
01:24:55,703 --> 01:25:01,608
But there's only one neighborhood
we know for sure that sustains life:
1172
01:25:06,247 --> 01:25:09,650
Earth.
1173
01:25:09,684 --> 01:25:14,154
GEOFF MARCY: The sun powers almost
everything here on the Earth.
1174
01:25:14,188 --> 01:25:17,057
It's the energy source; it's the engine
1175
01:25:17,091 --> 01:25:19,559
of life and many other processes.
1176
01:25:19,594 --> 01:25:25,299
And life here on Earth
is based heavily on water.
1177
01:25:25,333 --> 01:25:31,238
And it's liquid water that's the key
to life as we know it.
1178
01:25:31,272 --> 01:25:35,208
And it's because liquid water
serves as the solvent,
1179
01:25:35,243 --> 01:25:39,613
the cocktail mixer,
for the biochemistry of life.
1180
01:25:42,417 --> 01:25:45,452
NARRATOR: Earth is the only planet
in our solar system
1181
01:25:45,486 --> 01:25:48,855
with abundant liquid water.
1182
01:25:48,890 --> 01:25:51,124
As with any prime real estate,
1183
01:25:51,159 --> 01:25:55,128
it's all about location,
location, location.
1184
01:25:57,932 --> 01:26:00,167
MARCY: Venus is closer to the sun,
1185
01:26:00,201 --> 01:26:03,503
Mars is farther from the sun,
1186
01:26:03,538 --> 01:26:07,908
and there's a zone in between
the blazing hot furnace of Venus,
1187
01:26:07,942 --> 01:26:09,409
the frigid Mars,
1188
01:26:09,444 --> 01:26:12,346
that zone in between
we call the habitable zone,
1189
01:26:12,380 --> 01:26:14,915
and the Earth lies
smack in that thing,
1190
01:26:14,949 --> 01:26:18,585
where water would be
in liquid form,
1191
01:26:18,619 --> 01:26:23,590
not in steam, too hot,
not in ice form, too cold.
1192
01:26:23,624 --> 01:26:26,760
But rather a temperature that,
as Goldilocks said,
1193
01:26:26,794 --> 01:26:29,262
is just right for life.
1194
01:26:31,866 --> 01:26:34,134
NARRATOR: The location
of a habitable green zone
1195
01:26:34,168 --> 01:26:36,737
depends on the star.
1196
01:26:39,474 --> 01:26:45,078
With hot blue stars,
the green zone is further out.
1197
01:26:45,113 --> 01:26:50,150
With cooler red stars,
it's closer in.
1198
01:26:50,184 --> 01:26:55,589
Every star in the Milky Way
has a habitable zone.
1199
01:26:55,623 --> 01:26:59,726
But not every star has
planets within that zone.
1200
01:27:02,163 --> 01:27:06,633
MARCY: In 1995 something happened
that was extraordinary.
1201
01:27:06,667 --> 01:27:09,469
I got a call from my collaborator,
Paul Butler,
1202
01:27:09,504 --> 01:27:12,739
and all he said was, Geoff,
come over here.
1203
01:27:12,774 --> 01:27:16,777
And it was a moment
that I will never forget.
1204
01:27:16,811 --> 01:27:20,914
I was silent, Paul was silent,
and we were just stunned.
1205
01:27:20,948 --> 01:27:22,883
There on the computer screen
1206
01:27:22,917 --> 01:27:28,121
I saw the unmistakable
signature of a planet.
1207
01:27:30,224 --> 01:27:36,530
NARRATOR: Marcy had discovered
the first planet around another star.
1208
01:27:36,564 --> 01:27:38,799
But he couldn't actually see it
1209
01:27:38,833 --> 01:27:42,536
because the planet
was too small and dim.
1210
01:27:46,207 --> 01:27:51,878
MARCY: Any planet orbiting a star
is lost in the glare of that host star,
1211
01:27:51,913 --> 01:27:55,148
that outshines it
by a factor of a billion.
1212
01:27:55,183 --> 01:28:00,053
And so instead, to detect planets,
we watch the stars.
1213
01:28:00,087 --> 01:28:03,523
And in fact a star
will wobble in space
1214
01:28:03,558 --> 01:28:07,494
because it's yanked on
gravitationally by the planet,
1215
01:28:07,528 --> 01:28:10,363
or planets, orbiting that star.
1216
01:28:10,398 --> 01:28:12,432
And by watching the star alone
1217
01:28:12,467 --> 01:28:15,502
we can determine whether
the star has planets
1218
01:28:15,536 --> 01:28:19,806
and how far out those planets are
from the host star.
1219
01:28:21,709 --> 01:28:25,745
NARRATOR: So far astronomers
have found over 400 planets
1220
01:28:25,780 --> 01:28:28,482
orbiting stars in our galaxy.
1221
01:28:28,516 --> 01:28:32,719
But none of them seem to be
in habitable zones.
1222
01:28:32,753 --> 01:28:37,090
MARCY: One type of giant planet
orbits very close to its star.
1223
01:28:37,124 --> 01:28:38,592
We call them hot Jupiters,
1224
01:28:38,626 --> 01:28:41,495
because these Jupiter-like planets
are so close
1225
01:28:41,529 --> 01:28:47,667
that they're blow-torched
by the intense heat from the star.
1226
01:28:47,702 --> 01:28:51,204
The other sort of planet
we've found is also bizarre.
1227
01:28:51,239 --> 01:28:55,208
We've found planets that orbit
in elongated orbits,
1228
01:28:55,243 --> 01:28:57,644
elliptical, stretched out orbits,
1229
01:28:57,678 --> 01:28:59,746
but then the planets
go very far from the star
1230
01:28:59,780 --> 01:29:03,483
where they would be quite cold.
1231
01:29:03,518 --> 01:29:06,253
And so the planets
that we've found so far
1232
01:29:06,287 --> 01:29:09,523
are a little too weird
for us to imagine
1233
01:29:09,557 --> 01:29:13,560
that life would have
a good chance of surviving.
1234
01:29:13,594 --> 01:29:14,995
MAN: Power on.
1235
01:29:15,029 --> 01:29:16,263
External.
1236
01:29:16,297 --> 01:29:21,134
NARRATOR: But all that may be
about to change.
1237
01:29:21,168 --> 01:29:27,340
Recently NASA launched
a powerful new telescope called Kepler,
1238
01:29:27,375 --> 01:29:29,376
to hunt for Earth-sized planets
1239
01:29:29,410 --> 01:29:33,747
that may orbit habitable zones
around nearby stars.
1240
01:29:36,484 --> 01:29:39,753
MARCY: Kepler works
in the most simple way.
1241
01:29:39,787 --> 01:29:45,091
All Kepler does is monitor
the brightness of 100,000 stars
1242
01:29:45,126 --> 01:29:47,694
with such exquisite precision
1243
01:29:47,728 --> 01:29:51,498
that it would detect a planet
as small as an Earth-like one
1244
01:29:51,532 --> 01:29:54,935
as it blocks the starlight.
1245
01:29:54,969 --> 01:29:56,670
NARRATOR: We see
the same thing from Earth
1246
01:29:56,704 --> 01:30:01,041
when Venus and Mercury
are silhouetted against the sun.
1247
01:30:04,145 --> 01:30:08,014
But Kepler's task is far more difficult.
1248
01:30:10,151 --> 01:30:12,919
MARCY: It's a little bit like
having a searchlight
1249
01:30:12,954 --> 01:30:16,423
in which you're trying to detect
any dust on that searchlight
1250
01:30:16,457 --> 01:30:18,658
by noticing a dimming
of the searchlight
1251
01:30:18,693 --> 01:30:23,964
when one dust particle falls
on this massive searchlight.
1252
01:30:23,998 --> 01:30:25,532
NARRATOR: From this tiny dimming,
1253
01:30:25,566 --> 01:30:29,636
the size of the planet
can be measured.
1254
01:30:29,670 --> 01:30:34,107
And together with the way it
causes its host star to wobble,
1255
01:30:34,141 --> 01:30:37,043
Marcy can work out its density.
1256
01:30:38,512 --> 01:30:40,413
MARCY: And of course
this is glorious
1257
01:30:40,448 --> 01:30:42,749
because by these measurements
1258
01:30:42,783 --> 01:30:45,552
we'll be able to distinguish
gaseous planets,
1259
01:30:45,586 --> 01:30:47,854
probably not suitable for life,
1260
01:30:47,888 --> 01:30:53,560
from the rocky planets that may have
a surface covered by liquid water.
1261
01:30:55,196 --> 01:31:00,100
NARRATOR: Astronomers aren't sure
how many planets Kepler will find--
1262
01:31:00,134 --> 01:31:03,903
but with 200 billion stars
in the Milky Way,
1263
01:31:03,938 --> 01:31:08,308
the odds look promising.
1264
01:31:08,342 --> 01:31:12,312
Seth Shostak has done the math.
1265
01:31:12,346 --> 01:31:13,847
SETH SHOSTAK: You know,
the indications are
1266
01:31:13,881 --> 01:31:16,249
a lot of those stars have planets,
maybe half of them do.
1267
01:31:16,283 --> 01:31:18,451
And since planets, you know,
being like kittens,
1268
01:31:18,486 --> 01:31:20,553
you don't just get one,
you get a couple.
1269
01:31:20,588 --> 01:31:24,724
There are probably on the order
of a million million planets out there.
1270
01:31:27,395 --> 01:31:29,329
NARRATOR: A trillion planets.
1271
01:31:29,363 --> 01:31:33,333
It's an unimaginably vast number.
1272
01:31:33,367 --> 01:31:35,935
But what are the chances
of them being in a location
1273
01:31:35,970 --> 01:31:39,806
where life can flourish?
1274
01:31:39,840 --> 01:31:44,210
MARCY: We can expand the idea
of a habitable zone around a star
1275
01:31:44,245 --> 01:31:49,849
to a habitable zone within
our entire Milky Way galaxy.
1276
01:31:51,052 --> 01:31:53,286
NARRATOR: The search for life begins
1277
01:31:53,320 --> 01:31:57,357
with the search
for a galactic habitable zone,
1278
01:31:57,391 --> 01:32:01,094
the safe haven that
allows life to flourish.
1279
01:32:02,863 --> 01:32:06,599
MARCY: In close, at the hub
there is an extraordinary amount
1280
01:32:06,634 --> 01:32:10,804
of X-rays, harsh radio waves,
even gamma rays
1281
01:32:10,838 --> 01:32:15,475
that would certainly destroy
fragile single-celled life
1282
01:32:15,509 --> 01:32:20,447
just getting a start
toward evolution.
1283
01:32:20,481 --> 01:32:22,649
SHOSTAK: Downtown is dangerous.
1284
01:32:22,683 --> 01:32:24,751
There's a super massive
black hole down there.
1285
01:32:24,785 --> 01:32:29,289
You get too close to that, all sorts
of bad things can happen.
1286
01:32:29,323 --> 01:32:30,757
There are also a lot
of stars down there
1287
01:32:30,791 --> 01:32:32,692
and, you know, a lot of stars
sounds good,
1288
01:32:32,727 --> 01:32:35,795
but on the other hand
if you have too many nearby stars
1289
01:32:35,830 --> 01:32:40,700
they tend to shake up all the comets
in your solar system
1290
01:32:40,735 --> 01:32:42,102
that are constantly
pummeling you
1291
01:32:42,136 --> 01:32:44,971
with these collisions that,
just ask the dinosaurs,
1292
01:32:45,005 --> 01:32:48,074
are not always good for you.
1293
01:32:48,109 --> 01:32:49,843
NARRATOR: The spiral arms may offer
1294
01:32:49,877 --> 01:32:53,546
the safest neighborhoods
in the galaxy.
1295
01:32:53,581 --> 01:32:57,951
But even here, danger
may lurk around the corner.
1296
01:32:59,320 --> 01:33:01,788
SHOSTAK: If you happen to be
on a planet near a supernova,
1297
01:33:01,822 --> 01:33:04,824
that explosion could ruin
your whole day.
1298
01:33:04,859 --> 01:33:06,893
Life might get started,
and then, you know,
1299
01:33:06,927 --> 01:33:10,830
another couple of hundred
million years later it gets wiped out.
1300
01:33:10,865 --> 01:33:13,700
So these areas are sort of
no-go zones, no man's land.
1301
01:33:13,734 --> 01:33:16,569
Well, no alien's land, perhaps.
1302
01:33:16,604 --> 01:33:20,707
NARRATOR: The outer reaches
of our Milky Way are quieter.
1303
01:33:20,741 --> 01:33:25,612
But here life would still
find it difficult to take root.
1304
01:33:25,646 --> 01:33:28,715
MARCY: At the outskirts
of our Milky Way galaxy
1305
01:33:28,749 --> 01:33:30,650
there aren't very many
heavy elements
1306
01:33:30,684 --> 01:33:33,853
of which the cells of our bodies
and life as we know it
1307
01:33:33,888 --> 01:33:35,054
are composed.
1308
01:33:35,089 --> 01:33:38,825
And so we may not have
the essential building blocks of life
1309
01:33:38,859 --> 01:33:42,629
at the outer edges
of our own Milky Way.
1310
01:33:45,399 --> 01:33:50,103
NARRATOR: So it's not an accident
that we are where we are.
1311
01:33:50,137 --> 01:33:54,440
Our neighborhood, tucked away
between two spiral arms,
1312
01:33:54,475 --> 01:33:57,210
is prime real estate.
1313
01:33:57,244 --> 01:34:02,448
It's remained relatively unchanged
for billions of years,
1314
01:34:02,483 --> 01:34:07,453
giving life time
to establish and evolve.
1315
01:34:11,592 --> 01:34:15,128
Other advanced civilizations,
if they exist,
1316
01:34:15,162 --> 01:34:18,431
are likely to live
in similar neighborhoods,
1317
01:34:18,465 --> 01:34:21,935
cocooned from the dangers
of the galaxy.
1318
01:34:24,772 --> 01:34:28,007
We haven't found them yet.
1319
01:34:28,042 --> 01:34:32,812
But then again,
our galaxy's a big place.
1320
01:34:35,182 --> 01:34:36,850
SHOSTAK: We haven't found
any life elsewhere,
1321
01:34:36,884 --> 01:34:38,184
we haven't found pond scum,
1322
01:34:38,219 --> 01:34:40,286
we haven't found
dead pond scum anywhere else,
1323
01:34:40,321 --> 01:34:42,789
not convincingly,
and why is that?
1324
01:34:42,823 --> 01:34:46,092
Well, fewer than a thousand stars
have been looked at carefully
1325
01:34:46,126 --> 01:34:48,661
for planets that might have
intelligent life.
1326
01:34:48,696 --> 01:34:51,731
So you know, it's sort of
like going to Africa
1327
01:34:51,765 --> 01:34:54,934
looking for mega fauna, you know,
elephants, giraffes, something like that,
1328
01:34:54,969 --> 01:34:56,669
and you land in Africa
1329
01:34:56,704 --> 01:34:59,272
and you look at the first
square yard of real estate there
1330
01:34:59,306 --> 01:35:01,608
and you say no elephants here,
then you give up.
1331
01:35:01,642 --> 01:35:04,744
Well, we shouldn't give up,
we're just beginning.
1332
01:35:04,778 --> 01:35:09,716
MARCY: Well, if we do find life,
1333
01:35:09,750 --> 01:35:16,589
it's amazing, if we find life
elsewhere in the universe,
1334
01:35:16,624 --> 01:35:21,828
I think the stock market
won't budge one bit.
1335
01:35:21,862 --> 01:35:26,532
But we humans will know,
for the first time in human history,
1336
01:35:26,567 --> 01:35:29,002
that we're not alone.
1337
01:35:29,036 --> 01:35:33,106
That we have kindred spirits
out among the stars,
1338
01:35:33,140 --> 01:35:38,444
and that our destiny may well be
to venture to the stars,
1339
01:35:38,479 --> 01:35:40,313
communicate with them
1340
01:35:40,347 --> 01:35:45,118
and become members
of a great galactic country club.
110392
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