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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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00:16:36,263 --> 00:16:40,267
In infrared light, a telescope
can see through it.
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00:16:40,300 --> 00:16:41,702
The infrared camera,
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if I put my hand inside,
can see my hand.
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00:16:45,505 --> 00:16:48,275
I'll wiggle my fingers
to show you.
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00:16:48,308 --> 00:16:52,112
But you're seeing the heat
from my hand inside the bag,
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00:16:52,145 --> 00:16:57,084
and this is just like a star that's
hidden inside a cloud of gas and dust,
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00:16:57,117 --> 00:17:01,788
that infrared astronomers can detect
by using an infrared telescope.
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00:17:04,791 --> 00:17:09,162
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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00:17:15,535 --> 00:17:20,540
and we want to be able to look inside
this nebula and see the stars.
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00:17:20,574 --> 00:17:22,809
In infrared light, in this image,
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00:17:22,843 --> 00:17:27,647
we can now pick out the stars
inside the nebula,
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00:17:27,681 --> 00:17:32,119
and we can see dusty cocoons
around the stars.
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00:17:32,152 --> 00:17:38,058
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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00:17:43,563 --> 00:17:46,199
The way to do that is
with an X-ray picture.
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00:17:46,233 --> 00:17:48,969
Now when we transition
into the X-ray image,
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00:17:49,002 --> 00:17:51,271
you can see just
the stars themselves,
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00:17:51,304 --> 00:17:54,541
the X-rays coming
from the surfaces of the stars,
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and now we can study them
in great detail.
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00:18:00,680 --> 00:18:03,550
NARRATOR: By analyzing the light
from these stars,
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00:18:03,583 --> 00:18:07,621
astronomers make
an astounding discovery.
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00:18:10,423 --> 00:18:17,030
Hidden within the Orion Nebula are some
of the youngest stars ever found...
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00:18:17,063 --> 00:18:21,001
stars just a few
hundred thousand years old...
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00:18:21,034 --> 00:18:25,205
a mere heartbeat
in the life of the galaxy.
229
00:18:25,238 --> 00:18:28,408
And it's not just the Orion Nebula.
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Nebulas house baby stars
in every spiral arm of the galaxy.
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00:18:39,252 --> 00:18:42,389
BULLOCK: These regions
are the nurseries for new stars.
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00:18:42,422 --> 00:18:44,291
There are young stars
in these regions
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00:18:44,324 --> 00:18:47,060
that are heating up gas clouds
that surround them
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00:18:47,093 --> 00:18:50,697
and making those
gas clouds glow pink.
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00:18:50,730 --> 00:18:53,433
Stars are made out of gas, basically,
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00:18:53,466 --> 00:18:55,368
and our galaxy has gas.
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00:18:55,402 --> 00:18:57,437
In fact, our galaxy, you can think of it
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00:18:57,470 --> 00:18:59,539
as having an atmosphere
of gas and dust
239
00:18:59,573 --> 00:19:02,008
that surrounds all of the stars
that we see in the disc,
240
00:19:02,042 --> 00:19:06,112
and it's from this gas
that new stars are born.
241
00:19:06,146 --> 00:19:10,584
NARRATOR: By observing nebulas
at different stages in their evolution,
242
00:19:10,617 --> 00:19:16,756
the story of a star's birth
begins to emerge.
243
00:19:16,790 --> 00:19:23,463
It all starts inside a cold, dark cloud
of dust and hydrogen gas,
244
00:19:23,496 --> 00:19:27,934
where a quiet tug of war begins.
245
00:19:27,968 --> 00:19:32,572
The cloud wants to dissipate,
like smoke in the air,
246
00:19:32,606 --> 00:19:36,676
but gravity wants
to pull it together.
247
00:19:36,710 --> 00:19:38,044
KIRSHNER: They're in
a kind of balance
248
00:19:38,078 --> 00:19:43,683
between gravity pulling in
and gas pressure pushing back out.
249
00:19:43,717 --> 00:19:48,088
Gravity wins, and the material
crunches down into a disc
250
00:19:48,121 --> 00:19:52,826
that is the beginning
of becoming a star.
251
00:19:52,859 --> 00:19:55,295
NARRATOR: As gravity pulls
more and more gas
252
00:19:55,328 --> 00:19:57,931
towards the center of the disc,
253
00:19:57,964 --> 00:20:03,336
it gets denser and denser
and hotter and hotter...
254
00:20:06,907 --> 00:20:10,977
...until finally,
at 18 million degrees,
255
00:20:11,011 --> 00:20:15,115
a miraculous transformation
takes place.
256
00:20:15,148 --> 00:20:19,286
Hydrogen atoms fuse together
to form helium...
257
00:20:19,319 --> 00:20:25,158
and with a burst of nuclear energy,
a star begins to shine.
258
00:20:25,191 --> 00:20:30,196
KIRSHNER: These stars eventually get
their nuclear fires going in the core.
259
00:20:30,230 --> 00:20:32,432
And when they do, they heat up,
260
00:20:32,465 --> 00:20:35,335
they can expel the material
that's around them
261
00:20:35,368 --> 00:20:39,773
so that it kind of clears up
the neighborhood.
262
00:20:39,806 --> 00:20:42,909
NARRATOR: Over the next
few million years,
263
00:20:42,943 --> 00:20:49,215
winds blow the surrounding gas
into spectacular swirling patterns.
264
00:20:52,619 --> 00:20:56,156
KIRSHNER: It blows away the gas,
it blows away the dust
265
00:20:56,189 --> 00:20:58,224
and it lets us see
this beautiful new thing,
266
00:20:58,258 --> 00:21:00,260
this place where the star
has been born.
267
00:21:22,015 --> 00:21:24,584
NARRATOR: A human lifetime
is too short
268
00:21:24,617 --> 00:21:29,289
to witness the wonder of a star's birth
in the spiral arms.
269
00:21:29,322 --> 00:21:35,762
But by speeding up millions of years
of cosmic time into just a few seconds,
270
00:21:35,795 --> 00:21:39,332
we can see one star born
after another.
271
00:21:46,840 --> 00:21:51,878
Here and there are even more
brilliant flashes of light,
272
00:21:51,911 --> 00:21:56,449
coming from some of the most violent
and dangerous neighborhoods
273
00:21:56,483 --> 00:22:00,553
in the entire Milky Way galaxy.
274
00:22:00,587 --> 00:22:04,657
Here stars aren't born...
275
00:22:04,691 --> 00:22:06,426
they die.
276
00:22:19,205 --> 00:22:21,041
We're taking the Earth
277
00:22:21,074 --> 00:22:23,309
from the familiar neighborhood
of the sun
278
00:22:23,343 --> 00:22:26,446
to visit the wonders
of the Perseus Arm,
279
00:22:26,479 --> 00:22:31,151
nearly 6,500 light years away.
280
00:22:31,851 --> 00:22:37,590
Here lies one of the galaxy's
most beautiful sights...
281
00:22:37,624 --> 00:22:41,694
the Crab Nebula.
282
00:22:41,728 --> 00:22:49,335
Although it's made of gas and dust,
this nebula hasn't created stars... yet.
283
00:22:52,705 --> 00:22:54,641
But for Alex Filippenko,
284
00:22:54,674 --> 00:22:59,279
this area does represent
the industrial zone of our galaxy,
285
00:22:59,312 --> 00:23:04,451
where the building blocks of Earth
were manufactured long ago.
286
00:23:04,484 --> 00:23:08,721
ALEX FILIPPENKO: Look at that
molten iron. Holy moly!
287
00:23:08,755 --> 00:23:11,491
The Crab Nebula is a fascinating object.
288
00:23:11,524 --> 00:23:14,994
We see these very rapidly
expanding gases.
289
00:23:16,996 --> 00:23:21,434
NARRATOR: The crab may look static,
but gases are racing out from its center
290
00:23:21,468 --> 00:23:27,240
at over three million miles an hour,
291
00:23:27,273 --> 00:23:33,580
put into motion by a phenomenally
powerful and violent event in the past.
292
00:23:38,184 --> 00:23:40,887
FILIPPENKO: When we examine
the gases of the Crab Nebula,
293
00:23:40,920 --> 00:23:42,989
which are expanding outward,
294
00:23:43,022 --> 00:23:46,793
and we extrapolate that expansion
backward in time,
295
00:23:46,826 --> 00:23:49,395
we find that all of the gases
were at a common point
296
00:23:49,429 --> 00:23:52,532
about a thousand years ago.
297
00:23:56,202 --> 00:23:59,205
NARRATOR: Back on Earth,
a thousand years ago,
298
00:23:59,239 --> 00:24:03,243
early civilizations
watched the heavens.
299
00:24:03,276 --> 00:24:11,651
In 1054, Chinese manuscripts describe
the sudden arrival of a brilliant new star.
300
00:24:11,684 --> 00:24:19,058
It shines brighter than any other star,
so brightly it's visible during the day.
301
00:24:19,092 --> 00:24:23,296
But then it mysteriously disappears.
302
00:24:25,965 --> 00:24:31,237
Today, the Crab Nebula lies
in exactly the same part of the sky
303
00:24:31,271 --> 00:24:34,908
where the Chinese observed
their brilliant star.
304
00:24:37,177 --> 00:24:41,648
What they witnessed was
the moment the crab was born.
305
00:24:44,083 --> 00:24:45,652
FILIPPENKO: The Crab Nebula
was produced
306
00:24:45,685 --> 00:24:51,024
by the colossal titanic explosion
of a star at the end of its life.
307
00:24:51,057 --> 00:24:53,226
It's a supernova remnant.
308
00:24:55,762 --> 00:24:58,231
NARRATOR: The spiral arms
of our Milky Way
309
00:24:58,264 --> 00:25:02,835
are littered with these
colorful remnants.
310
00:25:02,869 --> 00:25:06,773
Tombstones of stars
that died violently
311
00:25:06,806 --> 00:25:11,578
in cataclysmic explosions
called supernovas.
312
00:25:14,681 --> 00:25:19,719
To figure out this mystery, astronomers
need to locate the next victim...
313
00:25:19,752 --> 00:25:23,656
a massive star at the brink of death.
314
00:25:25,725 --> 00:25:27,760
FILIPPENKO: Astronomers
are like detectives.
315
00:25:27,794 --> 00:25:30,697
We have to figure out
what's going on in the universe
316
00:25:30,730 --> 00:25:34,000
sometimes based on
a minimal number of clues,
317
00:25:34,033 --> 00:25:39,172
and in the case of most astronomers,
the clues come from only the light.
318
00:25:41,140 --> 00:25:44,744
NARRATOR: Andy Howell knows
catching light from a supernova
319
00:25:44,777 --> 00:25:47,747
is all about timing.
320
00:25:49,249 --> 00:25:52,418
ANDY HOWELL: Supernovae happen
about once every 70 years
321
00:25:52,452 --> 00:25:53,820
in a galaxy on average,
322
00:25:53,853 --> 00:25:56,189
so about the human lifetime.
323
00:25:56,222 --> 00:25:59,492
So chances are you're not going
to see one in your lifetime.
324
00:25:59,525 --> 00:26:02,528
In fact the last one in our galaxy
that anybody saw
325
00:26:02,562 --> 00:26:04,664
was about 400 years ago.
326
00:26:04,697 --> 00:26:06,866
So it's been a long time,
327
00:26:06,899 --> 00:26:09,636
and, you know, I study
supernovae for a living.
328
00:26:09,669 --> 00:26:15,041
I couldn't do this if I had to just
wait for one in our galaxy.
329
00:26:15,074 --> 00:26:17,977
NARRATOR: But thankfully
for Howell and Filippenko,
330
00:26:18,011 --> 00:26:20,880
there's no shortage of galaxies.
331
00:26:23,149 --> 00:26:27,887
HOWELL: So what we do is we look
at other galaxies, more distant galaxies.
332
00:26:27,920 --> 00:26:30,323
There are billions
of galaxies out there,
333
00:26:30,356 --> 00:26:34,694
and we see the supernovae
that happen in those galaxies.
334
00:26:34,727 --> 00:26:39,799
And if you look at 70 galaxies,
on average you'll find one a year.
335
00:26:39,832 --> 00:26:43,736
If you look at 700 galaxies,
you'll find ten a year, and so on.
336
00:26:43,770 --> 00:26:45,271
FILIPPENKO: There's power in numbers.
337
00:26:45,305 --> 00:26:51,778
If we look at thousands of galaxies,
we improve our odds tremendously.
338
00:26:51,811 --> 00:26:53,713
NARRATOR: This is a supernova
339
00:26:53,746 --> 00:26:57,850
that Filippenko and his colleagues
are lucky enough to catch...
340
00:26:57,884 --> 00:27:05,925
an exploding star on the outskirts
of a galaxy 55 million light years away.
341
00:27:05,958 --> 00:27:09,962
It briefly outshines
the entire galaxy...
342
00:27:09,996 --> 00:27:16,135
the light of a billion suns
distilled into one dying star.
343
00:27:18,071 --> 00:27:19,839
HOWELL: It takes supernova light
344
00:27:19,872 --> 00:27:22,709
a million, or even
a billion years to get here
345
00:27:22,742 --> 00:27:25,378
if they're millions or billions
of light years away.
346
00:27:25,411 --> 00:27:27,513
But they only shine
for about a month,
347
00:27:27,547 --> 00:27:30,783
so we have this little tiny window
to study these things
348
00:27:30,817 --> 00:27:33,419
before that light is gone forever.
349
00:27:33,453 --> 00:27:36,222
NARRATOR: In the workshop,
Howell and his team
350
00:27:36,255 --> 00:27:39,659
are busy preparing
their telescopes.
351
00:27:40,727 --> 00:27:43,563
HOWELL: Pretty cool.
WOMAN: That's right.
352
00:27:43,596 --> 00:27:45,898
HOWELL: We're building
a network of telescopes
353
00:27:45,932 --> 00:27:48,668
so that we can study supernovae
in greater numbers,
354
00:27:48,701 --> 00:27:52,238
in greater detail, than we've
ever been able to before.
355
00:27:54,474 --> 00:27:56,476
Let me show you the telescopes
we're building.
356
00:27:56,509 --> 00:27:58,945
These are the 0.4 meter telescopes
357
00:27:58,978 --> 00:28:00,847
and there are four of them here,
358
00:28:00,880 --> 00:28:04,350
and we're building them,
20 of them in total,
359
00:28:04,384 --> 00:28:06,185
and putting them
all around the world.
360
00:28:06,219 --> 00:28:08,955
So some of these first ones
will go to Chile,
361
00:28:08,988 --> 00:28:11,691
we have some in Hawaii already.
362
00:28:11,724 --> 00:28:13,493
So let me show you one
of the bigger telescopes
363
00:28:13,526 --> 00:28:15,428
we're building here.
364
00:28:15,461 --> 00:28:17,663
Here we have
the one meter telescope.
365
00:28:17,697 --> 00:28:19,499
We're building about fifteen.
366
00:28:19,532 --> 00:28:22,235
The mirror's not here yet, but this
is where it's going to go.
367
00:28:22,268 --> 00:28:25,204
That will reflect the light
we gather from the supernova.
368
00:28:25,238 --> 00:28:27,440
We have to be able to point
anywhere in the sky,
369
00:28:27,473 --> 00:28:30,777
and so you can see that the telescope
pivots along this axis,
370
00:28:30,810 --> 00:28:33,079
and this C ring moves.
371
00:28:36,182 --> 00:28:37,984
The great thing about
this kind of observing
372
00:28:38,017 --> 00:28:40,052
is that it's totally robotic,
373
00:28:40,086 --> 00:28:42,355
and I can just sit here
in Santa Barbara
374
00:28:42,388 --> 00:28:45,758
and have a beer and pizza
while the telescopes do their work.
375
00:28:45,792 --> 00:28:51,097
All new discoveries about supernovae
from all different places in the universe.
376
00:28:51,130 --> 00:28:54,100
NARRATOR: Once they've caught
the light of a dying star,
377
00:28:54,133 --> 00:28:56,569
the detective work begins.
378
00:28:58,371 --> 00:29:01,941
FILIPPENKO: We collect that light
and we analyze it in great detail
379
00:29:01,974 --> 00:29:04,444
in order to determine
what's going on,
380
00:29:04,477 --> 00:29:06,679
what's the chemical makeup
of the star,
381
00:29:06,712 --> 00:29:08,881
what's the pressure inside,
what's the temperature,
382
00:29:08,915 --> 00:29:11,451
what kind of nuclear reactions
are going on,
383
00:29:11,484 --> 00:29:13,453
how does a star explode.
384
00:29:13,486 --> 00:29:18,591
All of these things we figured out
through the analysis of light.
385
00:29:21,294 --> 00:29:25,498
NARRATOR: Astronomers deduce
that only stars with a huge mass
386
00:29:25,531 --> 00:29:27,633
go out with a bang.
387
00:29:30,236 --> 00:29:33,940
FILIPPENKO: A massive star has
a very interesting and vigorous life.
388
00:29:33,973 --> 00:29:37,510
Initially it fuses hydrogen
to form helium,
389
00:29:37,543 --> 00:29:38,845
and that produces energy.
390
00:29:38,878 --> 00:29:41,080
That makes the star shine.
391
00:29:41,113 --> 00:29:43,983
Then the ashes of that reaction,
the helium,
392
00:29:44,016 --> 00:29:46,552
fuse together to form
carbon and oxygen,
393
00:29:46,586 --> 00:29:48,588
releasing yet more energy.
394
00:29:48,621 --> 00:29:52,191
Then the carbon and oxygen
can fuse into still heavier elements,
395
00:29:52,225 --> 00:29:55,795
magnesium and sodium and neon
and things like that,
396
00:29:55,828 --> 00:29:59,999
and then silicon and sulfur,
and finally iron.
397
00:30:00,032 --> 00:30:05,438
NARRATOR: When it starts to make iron,
the giant star is doomed.
398
00:30:07,940 --> 00:30:11,878
In the core a fierce battle
takes place:
399
00:30:11,911 --> 00:30:16,148
energy pushes outwards,
holding it up,
400
00:30:16,182 --> 00:30:19,785
while gravity wants
to crush it inwards.
401
00:30:21,854 --> 00:30:28,194
The battle continues as the star
makes heavier and heavier elements...
402
00:30:28,227 --> 00:30:32,798
producing energy while
fending off total collapse.
403
00:30:36,102 --> 00:30:41,374
But once it starts to form iron,
the battle is lost.
404
00:30:45,645 --> 00:30:48,848
FILIPPENKO: Fusion of iron nuclei
into heavier things
405
00:30:48,881 --> 00:30:52,218
does not release energy,
it absorbs energy.
406
00:30:52,251 --> 00:30:54,554
So an iron core builds up,
407
00:30:54,587 --> 00:30:58,558
but finally it becomes
so massive that gravity wins.
408
00:30:58,591 --> 00:31:00,860
The iron core collapses.
409
00:31:00,893 --> 00:31:04,564
In less than a second
the outer layers collapse inward,
410
00:31:04,597 --> 00:31:08,367
then rebound and get blown
to smithereens.
411
00:31:28,621 --> 00:31:35,127
NARRATOR: But from this death
comes new life.
412
00:31:35,161 --> 00:31:39,599
[train horn blows]
413
00:31:49,775 --> 00:31:54,313
[horn blows]
414
00:31:54,347 --> 00:31:56,015
FILIPPENKO: We're at a foundry here,
415
00:31:56,048 --> 00:32:00,886
and they're pouring molten iron
from old machinery,
416
00:32:00,920 --> 00:32:04,390
and they're going to make parts
for new machines out of that iron.
417
00:32:04,423 --> 00:32:06,292
So they're recycling it.
418
00:32:06,325 --> 00:32:10,396
But all that iron was created
and ejected into the cosmos
419
00:32:10,429 --> 00:32:15,101
by gigantic stars that exploded
as supernovae.
420
00:32:16,836 --> 00:32:20,906
Those explosions created the iron,
ejected it into the cosmos,
421
00:32:20,940 --> 00:32:24,910
and then it got incorporated
into planetary systems like ours.
422
00:32:24,944 --> 00:32:31,617
But ultimately the atoms of iron
were created by exploding stars.
423
00:32:31,651 --> 00:32:37,823
NARRATOR: Supernovas are
the industrial zones of our star city...
424
00:32:37,857 --> 00:32:42,194
cosmic foundries
that forge new elements.
425
00:32:45,564 --> 00:32:47,767
In catastrophic explosions
426
00:32:47,800 --> 00:32:51,504
heavy elements are spewed out
into our galaxy,
427
00:32:51,537 --> 00:32:55,374
enriching it over billions of years.
428
00:32:55,408 --> 00:32:58,277
FILIPPENKO: So if some stars
were not to explode
429
00:32:58,310 --> 00:33:02,515
in the industrial zones
of galaxies like our Milky Way,
430
00:33:02,548 --> 00:33:06,519
then we wouldn't have these
industrial zones here on Earth.
431
00:33:06,552 --> 00:33:07,920
It all is linked.
432
00:33:07,953 --> 00:33:11,724
We're all linked to the cosmos.
433
00:33:11,757 --> 00:33:14,860
NARRATOR: Our lives today
are only possible
434
00:33:14,894 --> 00:33:19,765
because of events that happened
thousands of millions of years ago
435
00:33:19,799 --> 00:33:23,402
in the hearts of supernovas.
436
00:33:23,436 --> 00:33:26,505
[horn blows]
437
00:33:29,642 --> 00:33:34,380
FILIPPENKO: It's fascinating to realize
that the heavy elements in our bodies,
438
00:33:34,413 --> 00:33:37,883
the carbon in our cells,
the calcium in our bones,
439
00:33:37,917 --> 00:33:42,088
the oxygen that we breathe,
the iron in our red blood cells,
440
00:33:42,121 --> 00:33:45,591
all of those heavy elements
were synthesized,
441
00:33:45,624 --> 00:33:49,061
created through
nuclear reactions in stars
442
00:33:49,095 --> 00:33:53,632
and ejected into the cosmos
by supernovae.
443
00:33:57,937 --> 00:34:04,210
NARRATOR: But only a handful of stars
are massive enough to die as supernovas.
444
00:34:04,243 --> 00:34:10,483
Most stars, like our sun,
suffer a more gentle death.
445
00:34:10,516 --> 00:34:14,220
FILIPPENKO: Most stars don't die
in a cataclysmic explosion.
446
00:34:14,253 --> 00:34:17,089
Our own sun, for example,
a typical star,
447
00:34:17,123 --> 00:34:19,792
will die with a whimper,
not a bang.
448
00:34:24,697 --> 00:34:27,867
NARRATOR: Death comes
when the gravity pulling in
449
00:34:27,900 --> 00:34:33,305
finally succumbs
to the nuclear energy pushing out.
450
00:34:36,542 --> 00:34:42,515
When this happens, any star,
even our sun, will die.
451
00:34:44,817 --> 00:34:46,986
FILIPPENKO: In about
four or five billion years
452
00:34:47,019 --> 00:34:51,290
it'll grow into a much bigger star,
a star called a red giant,
453
00:34:51,323 --> 00:34:53,692
and the outer atmosphere of gases
454
00:34:53,726 --> 00:34:57,563
will be held so loosely
by the sun at that time
455
00:34:57,596 --> 00:35:03,202
that the gases will be blown away gently,
in what I call a cosmic burp.
456
00:35:05,237 --> 00:35:09,275
NARRATOR: These cosmic burps
leave behind dying stars
457
00:35:09,308 --> 00:35:15,648
that litter the spiral arms as they
slowly shed layers of elements.
458
00:35:17,016 --> 00:35:20,319
HOWELL: Some layers are oxygen
and some layers are silicon
459
00:35:20,352 --> 00:35:22,288
and some layers are sulfur,
460
00:35:22,321 --> 00:35:24,223
and those are
the different colors we see
461
00:35:24,256 --> 00:35:26,992
in the Hubble Space Telescope images.
462
00:35:29,295 --> 00:35:35,301
NARRATOR: Not far from our sun
is a place where a star is dying:
463
00:35:35,334 --> 00:35:38,504
the Helix Nebula.
464
00:35:38,537 --> 00:35:43,409
It sheds light on how
most stars end their lives.
465
00:35:47,012 --> 00:35:51,217
Our sun is destined to follow
a similar path when it dies,
466
00:35:51,250 --> 00:35:54,186
five billion years from now.
467
00:35:59,158 --> 00:36:01,861
But in other neighborhoods
in the galaxy,
468
00:36:01,894 --> 00:36:05,497
stars suffer a fate
worse than death.
469
00:36:05,531 --> 00:36:07,032
At the center of the galaxy
470
00:36:07,066 --> 00:36:11,470
lies a place where stars
disappear altogether.
471
00:36:11,503 --> 00:36:16,108
[people screaming]
472
00:36:22,648 --> 00:36:26,252
We're taking the Earth
from the safety of home
473
00:36:26,285 --> 00:36:30,756
to go downtown,
to the heart of the Milky Way.
474
00:36:34,560 --> 00:36:41,734
It's a dynamic, exciting district,
but it's also a risky place to hang out.
475
00:36:41,767 --> 00:36:44,136
[screaming]
476
00:36:44,169 --> 00:36:50,209
Andrea Ghez has spent over 15 years
exploring this neighborhood.
477
00:36:51,477 --> 00:36:54,013
ANDREA GHEZ: If we were to take a trip
from the spiral arms,
478
00:36:54,046 --> 00:36:56,081
out where we are by the sun,
479
00:36:56,115 --> 00:36:59,418
down to the center of the galaxy,
it would be an interesting trip.
480
00:36:59,451 --> 00:37:02,388
It would be very much like
moving from the suburbs
481
00:37:02,421 --> 00:37:09,194
into the heart of a very busy
metropolitan area.
482
00:37:09,228 --> 00:37:14,767
NARRATOR: As we head downtown,
the number of stars increases.
483
00:37:14,800 --> 00:37:19,204
GHEZ: So the density of stars is
tremendous at the center of the galaxy.
484
00:37:19,238 --> 00:37:23,242
It's about a billion times higher
than out here by the sun.
485
00:37:26,078 --> 00:37:29,214
NARRATOR: Here, at the center
of the galaxy,
486
00:37:29,248 --> 00:37:32,518
there are so many stars in the sky
487
00:37:32,551 --> 00:37:36,355
that the Earth is bathed
in perpetual light.
488
00:37:39,325 --> 00:37:45,097
It's a stunning but dangerous
sight to behold.
489
00:37:45,130 --> 00:37:48,968
The stars aren't just close together.
490
00:37:49,001 --> 00:37:51,971
They're moving at super speed.
491
00:37:56,575 --> 00:37:58,010
GHEZ: Going to the heart
of the galaxy
492
00:37:58,043 --> 00:38:02,014
might not be dissimilar to going
to an amusement park.
493
00:38:02,047 --> 00:38:04,483
The rides are somewhat similar
494
00:38:04,516 --> 00:38:08,020
to how the stars orbit
the center of the galaxy.
495
00:38:09,922 --> 00:38:14,159
Ten million miles per hour,
compared to, say, our sun,
496
00:38:14,193 --> 00:38:18,230
is about a factor of 50 times faster.
497
00:38:18,263 --> 00:38:21,767
So something has to be going on
at the center of our galaxy
498
00:38:21,800 --> 00:38:23,936
to make that happen.
499
00:38:25,838 --> 00:38:30,142
NARRATOR: But figuring out what
is no small task.
500
00:38:30,175 --> 00:38:35,881
The heart of our galaxy lies
26,000 light years away.
501
00:38:35,914 --> 00:38:37,616
It's difficult to observe
502
00:38:37,649 --> 00:38:42,921
through the vast amounts
of stars, gas and dust.
503
00:38:42,955 --> 00:38:46,992
And there's another problem
even closer to home:
504
00:38:47,026 --> 00:38:49,695
the Earth's atmosphere.
505
00:38:51,230 --> 00:38:52,531
GHEZ: The atmosphere
is great for us.
506
00:38:52,564 --> 00:38:54,199
It allows us to survive
here on Earth,
507
00:38:54,233 --> 00:38:57,870
but it's an absolute headache
for astronomers.
508
00:38:57,903 --> 00:38:59,438
It's very much like the problem
509
00:38:59,471 --> 00:39:02,107
of looking at a pebble
at the bottom of a stream.
510
00:39:02,141 --> 00:39:04,977
The water in the stream
is moving by and it's turbulent
511
00:39:05,010 --> 00:39:07,713
and it makes it very difficult
to get a clear vision.
512
00:39:07,746 --> 00:39:10,215
In the same way, looking
through the Earth's atmosphere
513
00:39:10,249 --> 00:39:15,888
prevents us from getting clear pictures
of the stars at the center of the galaxy.
514
00:39:15,921 --> 00:39:17,956
NARRATOR:
So astronomers like Ghez
515
00:39:17,990 --> 00:39:21,493
turn to a technique
called adaptive optics
516
00:39:21,527 --> 00:39:24,596
to get a better view.
517
00:39:24,630 --> 00:39:29,301
By measuring how a laser beam
is distorted in moving air,
518
00:39:29,334 --> 00:39:34,006
it's possible to compensate
for the atmosphere's blurring effect.
519
00:39:35,374 --> 00:39:37,409
GHEZ: So let me show you
an example
520
00:39:37,443 --> 00:39:40,112
of how powerful
adaptive optics is.
521
00:39:40,145 --> 00:39:41,313
The stars that we want to see
522
00:39:41,346 --> 00:39:43,749
are the ones that are
at the very center,
523
00:39:43,782 --> 00:39:44,983
and we think the heart
of the galaxy
524
00:39:45,017 --> 00:39:48,654
is right within the center of this box,
which is panned out here.
525
00:39:48,687 --> 00:39:52,191
Without adaptive optics, this region
looks completely blurry.
526
00:39:52,224 --> 00:39:54,126
You don't see the individual stars.
527
00:39:54,159 --> 00:39:59,765
With adaptive optics
you see the individual stars.
528
00:39:59,798 --> 00:40:03,769
NARRATOR: For 15 years Ghez
has taken infrared images
529
00:40:03,802 --> 00:40:06,672
of the stars at the heart
of the galaxy
530
00:40:06,705 --> 00:40:11,877
to produce an extraordinary
time-lapse movie.
531
00:40:11,910 --> 00:40:14,413
GHEZ: So if we zoom in
to the very heart of the galaxy
532
00:40:14,446 --> 00:40:16,181
we can actually see
the data that we've taken
533
00:40:16,215 --> 00:40:17,883
over the last 15 years,
534
00:40:17,916 --> 00:40:19,284
and you can see the stars
535
00:40:19,318 --> 00:40:21,186
and you can see the tremendous motion
that they've gone through.
536
00:40:21,220 --> 00:40:24,623
In particular SO-2,
which is my favorite star...
537
00:40:24,656 --> 00:40:26,658
every astronomer
has a favorite one...
538
00:40:26,692 --> 00:40:28,727
so you can see SO-2
goes around
539
00:40:28,760 --> 00:40:31,864
and in particular you can see,
as it gets to the center of the frame,
540
00:40:31,897 --> 00:40:33,465
it moves much more quickly.
541
00:40:33,499 --> 00:40:36,368
So something's interesting
as it goes through that region.
542
00:40:36,401 --> 00:40:39,638
So putting everything together,
all the measurements that we've made,
543
00:40:39,671 --> 00:40:41,406
we've been able to make
an animation
544
00:40:41,440 --> 00:40:47,045
that shows how the stars have moved
over the course of 15 years.
545
00:40:47,079 --> 00:40:50,749
Each star goes whipping
around the center of the galaxy.
546
00:40:50,782 --> 00:40:53,485
In particular the most striking thing
that you'll notice
547
00:40:53,519 --> 00:40:56,722
is the motion of SO-2.
548
00:40:56,755 --> 00:41:00,392
So SO-2 goes on an incredible
roller coaster ride.
549
00:41:00,425 --> 00:41:04,296
It comes whipping around
and then back out.
550
00:41:04,329 --> 00:41:07,099
NARRATOR: For an object to have
enough gravitational pull
551
00:41:07,132 --> 00:41:12,938
to send SO-2 on rapid orbit
around the center of the galaxy...
552
00:41:12,971 --> 00:41:17,309
it must also have a huge mass.
553
00:41:22,814 --> 00:41:26,218
GHEZ: SO-2 goes around
once every 15 years,
554
00:41:26,251 --> 00:41:31,857
and what it tells us is that there
is four million times the mass of the sun
555
00:41:31,890 --> 00:41:34,760
confined within its orbit.
556
00:41:37,996 --> 00:41:40,899
NARRATOR: Astronomers know
of only one contender
557
00:41:40,933 --> 00:41:45,837
that has a giant mass
but is so small.
558
00:41:45,871 --> 00:41:48,073
GHEZ: So that's an incredible
amount of mass
559
00:41:48,106 --> 00:41:49,975
inside a very small volume,
560
00:41:50,008 --> 00:41:54,646
and that's the key
to proving a black hole.
561
00:41:54,680 --> 00:41:57,382
NARRATOR: And so at the center
of our galaxy
562
00:41:57,416 --> 00:42:00,385
lies a massive black hole,
563
00:42:00,419 --> 00:42:06,458
an object whose gravity is so strong
not even light can escape it.
564
00:42:09,161 --> 00:42:14,166
This is a real image
of the center of our galaxy.
565
00:42:15,534 --> 00:42:17,970
We can't see the black hole...
566
00:42:18,003 --> 00:42:24,943
but we can see bright clouds
of dust and gas spiraling toward it.
567
00:42:27,980 --> 00:42:30,716
We're nearing the black hole.
568
00:42:30,749 --> 00:42:35,320
It's at the center of a stream
of dust and gas...
569
00:42:37,990 --> 00:42:43,528
...the debris of stars blown apart
after straying too close.
570
00:42:47,733 --> 00:42:49,668
GHEZ: Black holes grow with time,
571
00:42:49,701 --> 00:42:53,038
and that happens
by material falling onto it,
572
00:42:53,071 --> 00:42:54,606
accreting onto it,
573
00:42:54,640 --> 00:42:57,876
and that material can come
in the form of either gas
574
00:42:57,909 --> 00:43:03,715
or stars that get torn apart
by the black hole itself.
575
00:43:03,749 --> 00:43:08,787
NARRATOR: At the center
is the invisible black hole.
576
00:43:08,820 --> 00:43:13,592
This is the material it feeds on.
577
00:43:13,625 --> 00:43:17,996
The glowing region
is the accretion disc.
578
00:43:18,030 --> 00:43:20,732
Here star debris falls inward
579
00:43:20,766 --> 00:43:24,069
and whips around
at astonishing speed.
580
00:43:24,102 --> 00:43:28,340
Friction heats the debris up
to such high temperatures
581
00:43:28,373 --> 00:43:31,977
that it glows white hot.
582
00:43:32,010 --> 00:43:34,446
GHEZ: So at the center of our galaxy
we do have a black hole.
583
00:43:34,479 --> 00:43:36,114
We now know that today,
584
00:43:36,148 --> 00:43:39,818
but it's not producing
a tremendous amount of energy.
585
00:43:39,851 --> 00:43:43,522
So it's perhaps, we could say,
it's a black hole that's on a diet.
586
00:43:43,555 --> 00:43:48,260
It simply doesn't have
a lot of material to feast on.
587
00:43:48,293 --> 00:43:52,397
NARRATOR: But what would happen
if SO-2 and the other stars
588
00:43:52,431 --> 00:43:56,535
were pulled inward
by the black hole?
589
00:43:56,568 --> 00:43:59,471
GHEZ: What happens when
that material falls onto the black hole
590
00:43:59,504 --> 00:44:00,972
is that the black hole,
591
00:44:01,006 --> 00:44:03,642
there's radiation associated
with the black hole
592
00:44:03,675 --> 00:44:05,711
and it can generate these jets,
593
00:44:05,744 --> 00:44:09,648
squirting out from the center
of the galaxy.
594
00:44:09,681 --> 00:44:13,952
NARRATOR: Spewing out subatomic particles
close to the speed of light,
595
00:44:13,985 --> 00:44:18,323
the beams are like
vast cosmic searchlights.
596
00:44:30,068 --> 00:44:32,637
This is Messier 87,
597
00:44:32,671 --> 00:44:39,044
a large elliptical galaxy that has
a super massive black hole at its heart.
598
00:44:39,077 --> 00:44:43,749
It's feasting on its own stars.
599
00:44:43,782 --> 00:44:46,184
Shooting out from its bright core
600
00:44:46,218 --> 00:44:50,822
are jets that travel
over 5,000 light years.
601
00:44:52,557 --> 00:44:56,128
GHEZ: I like to call these
the prima donnas of the galaxy world.
602
00:44:56,161 --> 00:45:00,565
These are the ten percent
of galaxies that are showoffs.
603
00:45:03,668 --> 00:45:06,838
NARRATOR: Astronomers believe
that the massive black hole
604
00:45:06,872 --> 00:45:08,573
at the heart of the Milky Way
605
00:45:08,607 --> 00:45:12,043
has been there from the very start.
606
00:45:14,446 --> 00:45:18,216
But in order to get back
to where the galaxy first began,
607
00:45:18,250 --> 00:45:24,389
we have to travel out to the oldest
neighborhood in our star city.
608
00:45:35,233 --> 00:45:39,271
We're traveling upward,
away from our solar system,
609
00:45:39,304 --> 00:45:43,975
out of the spiral arms
of our Milky Way.
610
00:45:44,009 --> 00:45:51,483
Up ahead lie vast clusters of stars
that orbit the heart of our star city.
611
00:45:54,052 --> 00:45:57,856
There are over 150 of them.
612
00:46:00,425 --> 00:46:04,696
These satellite towns,
called globular clusters,
613
00:46:04,729 --> 00:46:10,735
hold the answer to one of
the greatest mysteries in astronomy:
614
00:46:10,769 --> 00:46:14,573
the true age of our galaxy.
615
00:46:17,609 --> 00:46:21,480
BULLOCK: Globular clusters are
really fascinating groups of stars.
616
00:46:21,513 --> 00:46:23,982
They contain about
a million stars each,
617
00:46:24,015 --> 00:46:26,084
and the thing that's
really cool about them
618
00:46:26,117 --> 00:46:30,789
is the stars are
really tightly packed.
619
00:46:30,822 --> 00:46:32,357
KIRSHNER: If you could visit
a globular cluster,
620
00:46:32,390 --> 00:46:35,460
the night sky would be
spectacular,
621
00:46:35,494 --> 00:46:39,431
where many of the stars would be
as bright as the full moon.
622
00:46:39,464 --> 00:46:44,135
And the nighttime sky in all directions
would be filled with bright nearby stars.
623
00:46:44,169 --> 00:46:46,571
There'd be like fireworks all the time.
624
00:46:49,841 --> 00:46:52,677
NARRATOR: Besides the sheer
number of stars,
625
00:46:52,711 --> 00:46:57,916
there's something even more intriguing
about these clusters.
626
00:46:57,949 --> 00:46:59,985
BULLOCK: One of the very interesting
aspects of globular clusters
627
00:47:00,018 --> 00:47:04,222
is there's no sign of young stars.
628
00:47:06,925 --> 00:47:10,996
NARRATOR: Stars are like people.
629
00:47:11,029 --> 00:47:15,500
Look at them,
and you can guess their age
630
00:47:15,534 --> 00:47:19,437
and the lives they've led.
631
00:47:19,471 --> 00:47:25,143
With people, gray hairs and wrinkles
are the telltale signs.
632
00:47:25,176 --> 00:47:28,980
With stars, it's color and size.
633
00:47:31,049 --> 00:47:33,018
BULLOCK: So the biggest stars,
the most massive stars,
634
00:47:33,051 --> 00:47:36,421
the ones with the most gas,
live life in the fast lane.
635
00:47:36,454 --> 00:47:38,557
They live very short
amounts of time.
636
00:47:38,590 --> 00:47:41,426
But they burn very brightly
and they're very, very hot,
637
00:47:41,459 --> 00:47:44,629
and so they tend to be blue.
638
00:47:44,663 --> 00:47:46,932
KIRSHNER: On the other hand
you have the red stars,
639
00:47:46,965 --> 00:47:50,135
which use their energy
very conservatively,
640
00:47:50,168 --> 00:47:53,338
last for a long time,
don't glow too brightly.
641
00:47:53,371 --> 00:47:56,508
And those stars last
for a very long time.
642
00:47:56,541 --> 00:47:58,376
BULLOCK: So by measuring
the brightnesses
643
00:47:58,410 --> 00:48:01,413
and the colors of the stars
in a globular cluster,
644
00:48:01,446 --> 00:48:03,081
we can figure out
how old they are.
645
00:48:03,114 --> 00:48:04,482
And here's the remarkable thing.
646
00:48:04,516 --> 00:48:06,651
They're very old.
647
00:48:06,685 --> 00:48:09,854
Globular clusters, at least the stars
in globular clusters,
648
00:48:09,888 --> 00:48:14,192
in many cases are almost
as old as the universe itself.
649
00:48:18,330 --> 00:48:22,634
NARRATOR: Globular clusters
are living fossils.
650
00:48:22,667 --> 00:48:25,537
They're like discovering
a community of people
651
00:48:25,570 --> 00:48:28,907
who've been around
since the stone age.
652
00:48:31,776 --> 00:48:37,415
Some stars here have been shining
for 12 billion years...
653
00:48:37,449 --> 00:48:40,819
more than twice as long as the sun.
654
00:48:40,852 --> 00:48:45,724
And that's a helpful tool in placing
an age on the Milky Way.
655
00:48:47,826 --> 00:48:50,161
BULLOCK: Globular clusters
are part of our galaxy.
656
00:48:50,195 --> 00:48:51,296
They orbit our galaxy.
657
00:48:51,329 --> 00:48:54,366
In some sense they're tracers
of our galaxy itself.
658
00:48:54,399 --> 00:48:56,935
And so by the fact that
the globular clusters are so old,
659
00:48:56,968 --> 00:48:59,804
it suggests that the galaxy is old.
660
00:49:02,807 --> 00:49:06,144
NARRATOR: And our galaxy
isn't just old...
661
00:49:06,177 --> 00:49:09,848
it's very old.
662
00:49:09,881 --> 00:49:16,087
In fact, the Milky Way is one
of the oldest objects in the cosmos.
663
00:49:16,121 --> 00:49:20,725
It's been around almost since
the beginning of the entire universe...
664
00:49:20,759 --> 00:49:23,695
at least 12 billion years.
665
00:49:25,797 --> 00:49:31,236
Globular clusters also show
that the chemistry of the galaxy back then
666
00:49:31,269 --> 00:49:35,473
was very different
from how it is today.
667
00:49:37,876 --> 00:49:40,779
KIRSHNER: We can measure
the chemical properties of those stars.
668
00:49:40,812 --> 00:49:45,283
Turns out they have very low abundances
of the heavy elements.
669
00:49:45,316 --> 00:49:49,087
Things like iron are very rare
in globular cluster stars,
670
00:49:49,120 --> 00:49:51,723
compared to a star like the sun.
671
00:49:53,758 --> 00:49:59,397
NARRATOR: That means the early galaxy
was a far less colorful place.
672
00:50:03,401 --> 00:50:06,604
Without heavy elements
there weren't the beautiful hues
673
00:50:06,638 --> 00:50:11,476
we see in nebulas and
supernova remnants today.
674
00:50:11,509 --> 00:50:16,815
Even more importantly...
it was a galaxy without life.
675
00:50:18,550 --> 00:50:23,822
It took billions of years for stars
to form enough heavy elements
676
00:50:23,855 --> 00:50:28,893
for the evolution of life to begin
anywhere in the Milky Way...
677
00:50:33,665 --> 00:50:35,633
...leaving many to wonder
678
00:50:35,667 --> 00:50:40,205
how the galaxy has managed
to keep going for so long.
679
00:50:46,044 --> 00:50:48,580
BULLOCK: One of the puzzles
about our galaxy
680
00:50:48,613 --> 00:50:52,150
is that we know that it's had
stars forming continuously
681
00:50:52,183 --> 00:50:54,486
for about the last
ten billion years.
682
00:50:54,519 --> 00:50:57,188
But at the rate it's eating up
its gas now,
683
00:50:57,222 --> 00:50:59,858
it's forming new stars,
it should burn out that gas soon.
684
00:50:59,891 --> 00:51:01,192
It should run out of fuel.
685
00:51:01,226 --> 00:51:03,661
And so there has to be
some source for new fuel.
686
00:51:03,695 --> 00:51:07,766
NARRATOR: That source must be
outside the galaxy.
687
00:51:07,799 --> 00:51:13,471
And recently astronomers
made a startling discovery:
688
00:51:13,505 --> 00:51:18,476
Globular clusters aren't the only
groups of stars orbiting the Milky Way.
689
00:51:18,510 --> 00:51:22,781
There are other tiny galaxies
circling our galaxy
690
00:51:22,814 --> 00:51:26,651
called ultra faint dwarf galaxies.
691
00:51:26,684 --> 00:51:28,353
BULLOCK: The reason
why we haven't known
692
00:51:28,386 --> 00:51:30,655
about these dwarf galaxies
for very long,
693
00:51:30,688 --> 00:51:33,625
these so-called
ultra faint dwarf galaxies,
694
00:51:33,658 --> 00:51:36,227
is that they contain
just a few hundred stars,
695
00:51:36,261 --> 00:51:38,029
a thousand stars.
696
00:51:38,062 --> 00:51:41,332
So you try to find a clump
of a thousand stars
697
00:51:41,366 --> 00:51:43,768
while looking through a mass
of a billion stars.
698
00:51:43,802 --> 00:51:44,803
It's not easy.
699
00:51:44,836 --> 00:51:46,604
This is a needle
in a haystack problem.
700
00:51:46,638 --> 00:51:48,807
And it's only because
we have the precise maps,
701
00:51:48,840 --> 00:51:51,242
it's the precision
of modern astronomy
702
00:51:51,276 --> 00:51:52,710
that's allowed us to discover
703
00:51:52,744 --> 00:51:55,780
these extremely interesting
dwarf galaxies.
704
00:51:58,082 --> 00:52:01,820
NARRATOR: These elusive bodies
may help solve the mystery
705
00:52:01,853 --> 00:52:04,722
of what's fueling the galaxy.
706
00:52:06,324 --> 00:52:10,128
BULLOCK: So these dwarf galaxies
are whizzing around our galaxy.
707
00:52:10,161 --> 00:52:11,663
They're in orbit around it.
708
00:52:11,696 --> 00:52:13,631
Now sometimes they get too close,
709
00:52:13,665 --> 00:52:16,100
and when they get too close
they get ripped apart.
710
00:52:16,134 --> 00:52:20,939
In fact they get eaten,
in some sense, by our galaxy.
711
00:52:20,972 --> 00:52:25,577
NARRATOR: This computer model
shows dwarf galaxies as colored discs
712
00:52:25,610 --> 00:52:28,746
with our galaxy in the center.
713
00:52:28,780 --> 00:52:34,118
Over time, our galaxy
pulls dwarf galaxies in,
714
00:52:34,152 --> 00:52:37,755
devours them, and uses
their gas and dust
715
00:52:37,789 --> 00:52:41,759
to eventually form new stars.
716
00:52:44,128 --> 00:52:45,396
BULLOCK: So in much the same way
717
00:52:45,430 --> 00:52:48,499
that a large city might sort of
cannibalize its neighbors,
718
00:52:48,533 --> 00:52:53,438
the Milky Way is cannibalizing
its dwarf galaxy population.
719
00:52:53,471 --> 00:52:56,507
NARRATOR: Globular clusters
and dwarf galaxies
720
00:52:56,541 --> 00:53:01,312
provide crucial insight
to just how old our galaxy is...
721
00:53:01,346 --> 00:53:06,084
and how it's managed
to survive for so long.
722
00:53:06,117 --> 00:53:11,089
These bodies were once thought
to mark the Milky Way's city limits,
723
00:53:11,122 --> 00:53:15,827
the very outer reaches
of our star city.
724
00:53:15,860 --> 00:53:20,565
But today astronomers
are rethinking all that.
725
00:53:20,598 --> 00:53:25,436
Our galaxy might be bigger
than what we can see,
726
00:53:25,470 --> 00:53:30,475
spreading out further
than we ever imagined.
727
00:53:34,445 --> 00:53:36,114
We're picking up our Earth
728
00:53:36,147 --> 00:53:39,384
and moving from our quiet suburb
to a new neighborhood
729
00:53:39,417 --> 00:53:42,620
in the outer spiral arm
of our galaxy.
730
00:53:42,654 --> 00:53:44,956
Here we'll uncover the mystery
731
00:53:44,989 --> 00:53:50,061
of what holds all the stars
in the Milky Way together.
732
00:53:52,664 --> 00:53:57,135
From our new address, the night sky
looks a little different.
733
00:53:57,168 --> 00:54:02,140
The Milky Way is smaller
and the sky darker.
734
00:54:02,173 --> 00:54:08,479
Here, tens of thousands of light years
away from the center of our galaxy,
735
00:54:08,513 --> 00:54:12,884
we're still bound
by the force of gravity.
736
00:54:15,453 --> 00:54:17,588
BULLOCK: Gravity is the force
that makes any two objects
737
00:54:17,622 --> 00:54:19,290
want to move towards each other.
738
00:54:23,428 --> 00:54:29,834
NARRATOR: On Earth, cities are built
with iron girders and concrete beams...
739
00:54:29,867 --> 00:54:35,773
an invisible scaffold which holds
buildings up against the pull of gravity.
740
00:54:38,476 --> 00:54:45,049
Without this scaffolding, skyscrapers
would crumble and bridges collapse.
741
00:54:48,419 --> 00:54:53,524
Gravity governs Earth
and the entire universe.
742
00:55:01,299 --> 00:55:06,537
Anything that has mass
has a gravitational pull.
743
00:55:06,571 --> 00:55:10,375
The more the mass,
the stronger the pull.
744
00:55:12,677 --> 00:55:19,484
With 200 billion stars,
the Milky Way has a huge mass...
745
00:55:19,517 --> 00:55:23,988
and a tremendous
gravitational attraction to match.
746
00:55:24,022 --> 00:55:29,293
So, like a building, our galaxy
also needs propping up
747
00:55:29,327 --> 00:55:32,430
against the force of gravity.
748
00:55:34,799 --> 00:55:36,868
BULLOCK: Imagine the disc
of our galaxy.
749
00:55:36,901 --> 00:55:38,803
If you just took a disc of stars
750
00:55:38,836 --> 00:55:39,837
and put it there,
751
00:55:39,871 --> 00:55:41,372
gravity would tend to make
752
00:55:41,406 --> 00:55:43,207
this disc collapse in on itself,
753
00:55:43,241 --> 00:55:45,276
and it would immediately
just fall together.
754
00:55:45,309 --> 00:55:47,712
That's not what we see
with the galaxy.
755
00:55:47,745 --> 00:55:51,015
What's actually going on is the stars
are orbiting around the center,
756
00:55:51,049 --> 00:55:52,784
and that's what keeps them
from falling in,
757
00:55:52,817 --> 00:55:56,788
in much the same way that the Earth
is orbiting around the sun.
758
00:55:57,922 --> 00:56:02,860
NARRATOR: The planets in our solar system
are in a delicate balance...
759
00:56:02,894 --> 00:56:05,630
gravity pulls them towards the sun
760
00:56:05,663 --> 00:56:11,836
while their orbital velocity wants
to fling them out into space.
761
00:56:13,704 --> 00:56:15,807
In order to stay balanced,
762
00:56:15,840 --> 00:56:20,878
planets further from the sun
must orbit more slowly.
763
00:56:22,246 --> 00:56:24,015
BULLOCK: If you go
to more distant planets
764
00:56:24,048 --> 00:56:25,483
at the edge of the solar system,
765
00:56:25,516 --> 00:56:28,219
they're going around the sun
much more slowly than the Earth is,
766
00:56:28,252 --> 00:56:31,089
and that's because
the gravity is weaker.
767
00:56:31,122 --> 00:56:36,194
NARRATOR: The same should hold true
for stars in the Milky Way.
768
00:56:36,227 --> 00:56:40,832
They all orbit the center
of the galaxy,
769
00:56:40,865 --> 00:56:45,837
but the stars in the outer arm
should be traveling more slowly
770
00:56:45,870 --> 00:56:49,507
than those closer
to the galaxy's heart.
771
00:56:49,540 --> 00:56:51,809
BULLOCK: What's interesting
is that's not what's going on.
772
00:56:55,446 --> 00:56:57,515
The stars in the outer parts
of the galaxy
773
00:56:57,548 --> 00:57:01,752
are spinning around just as quickly
as those in the inner parts.
774
00:57:01,786 --> 00:57:04,789
NARRATOR: And they're not
the only ones.
775
00:57:04,822 --> 00:57:07,658
BULLOCK: It's not just our galaxy;
it's every galaxy we look at.
776
00:57:07,692 --> 00:57:14,132
Every galaxy we look at seems to be
spinning too fast in its outer parts.
777
00:57:14,165 --> 00:57:15,533
NARRATOR: These speeding stars
778
00:57:15,566 --> 00:57:19,303
should be flung out
of the galaxy altogether.
779
00:57:19,337 --> 00:57:22,640
But they're not.
780
00:57:22,673 --> 00:57:25,243
BULLOCK: That is a puzzle.
781
00:57:25,276 --> 00:57:27,578
This means that there's
a lot more mass there
782
00:57:27,612 --> 00:57:29,547
that we just can't see.
783
00:57:31,616 --> 00:57:33,885
NARRATOR: Mass that produces
the gravity
784
00:57:33,918 --> 00:57:38,089
that holds these stars
in their orbits.
785
00:57:40,691 --> 00:57:43,628
But when astronomers
look for the mass,
786
00:57:43,661 --> 00:57:48,232
there appears to be
nothing there...
787
00:57:48,266 --> 00:57:55,773
leading cosmologists like Joel Primack
to an astounding conclusion.
788
00:57:55,806 --> 00:57:57,775
JOEL PRIMACK: All of the galaxies,
789
00:57:57,808 --> 00:58:01,279
all of the stars and gas and dust
and planets and everything else
790
00:58:01,312 --> 00:58:04,649
that we can see with
our greatest telescopes,
791
00:58:04,682 --> 00:58:09,954
represent about half of one percent
of what's actually out there.
792
00:58:09,987 --> 00:58:11,722
The rest is invisible.
793
00:58:11,756 --> 00:58:16,527
It's mostly some mysterious substance
that we call dark matter.
794
00:58:16,561 --> 00:58:18,763
BULLOCK: You can't see dark matter.
795
00:58:18,796 --> 00:58:21,265
The reason why you
can see normal matter
796
00:58:21,299 --> 00:58:24,502
is because light shines on it
and reflects off of it.
797
00:58:24,535 --> 00:58:26,237
That's how you can see me.
798
00:58:26,270 --> 00:58:27,405
Dark matter doesn't work that way.
799
00:58:27,438 --> 00:58:30,708
The light goes right through
the dark matter.
800
00:58:30,741 --> 00:58:34,645
The way we detect dark matter
is because it has mass.
801
00:58:34,679 --> 00:58:38,416
Anything with mass affects
other things via gravity.
802
00:58:38,449 --> 00:58:40,851
That's the golden rule of mass,
that's what mass does,
803
00:58:40,885 --> 00:58:45,056
it tugs on other things
because of gravity.
804
00:58:45,089 --> 00:58:50,895
NARRATOR: Without dark matter,
the Milky Way couldn't exist.
805
00:58:50,928 --> 00:58:52,396
BULLOCK: So the galaxy is spinning.
806
00:58:52,430 --> 00:58:55,833
The galaxy is spinning fairly rapidly.
807
00:58:55,866 --> 00:58:59,570
The reason why it can spin so rapidly
is because it has so much dark matter.
808
00:58:59,604 --> 00:59:03,774
The dark matter has a lot of mass
and therefore it has a lot of gravity,
809
00:59:03,808 --> 00:59:07,912
and that's what keeps the stars
whizzing around.
810
00:59:07,945 --> 00:59:10,114
If you were to magically take
all of the dark matter
811
00:59:10,147 --> 00:59:11,515
away from our galaxy,
812
00:59:11,549 --> 00:59:12,550
it would fly apart.
813
00:59:12,583 --> 00:59:14,185
The stars would just
keep going straight
814
00:59:14,218 --> 00:59:17,555
and in a very short amount of time
the galaxy would just be gone.
815
00:59:17,588 --> 00:59:22,093
PRIMACK: There'd be just a mess
of stuff flying every which way.
816
00:59:22,126 --> 00:59:23,828
And that's not just true
of our galaxy,
817
00:59:23,861 --> 00:59:25,096
it's true of every galaxy
818
00:59:25,129 --> 00:59:27,865
and every cluster of galaxies
in the universe.
819
00:59:27,898 --> 00:59:31,936
They're all held together
by this invisible stuff
820
00:59:31,969 --> 00:59:34,338
that we call dark matter.
821
00:59:34,372 --> 00:59:37,875
BULLOCK: So we need the dark matter.
822
00:59:37,908 --> 00:59:40,811
It's the glue that holds
galaxies together.
823
00:59:43,481 --> 00:59:45,583
NARRATOR: The discovery
of dark matter
824
00:59:45,616 --> 00:59:50,321
has revolutionized our picture
of the Milky Way.
825
00:59:50,354 --> 00:59:56,594
The stars of the galaxy represent
just a fraction of its mass.
826
00:59:56,627 --> 01:00:02,400
The rest is made up of an invisible halo
of dark matter...
827
01:00:02,433 --> 01:00:08,739
surrounding every single star
and every creature in the galaxy.
828
01:00:11,342 --> 01:00:14,078
PRIMACK: The stars are
just the central region.
829
01:00:14,111 --> 01:00:16,947
The halo is at least ten times bigger
830
01:00:16,981 --> 01:00:20,451
and weighs much more
than ten times more
831
01:00:20,484 --> 01:00:24,355
than all the stars and gas and dust
that we can see.
832
01:00:24,388 --> 01:00:29,727
It's that whole structure
that's the real Milky Way galaxy.
833
01:00:29,760 --> 01:00:31,329
And that's not just true
of our galaxy,
834
01:00:31,362 --> 01:00:34,365
it's true of every galaxy
we've ever studied.
835
01:00:36,734 --> 01:00:42,973
NARRATOR: But dark matter does more
than simply hold galaxies together.
836
01:00:43,007 --> 01:00:46,510
Astronomers now think
it binds the Milky Way
837
01:00:46,544 --> 01:00:53,818
into an extraordinary structure
with billions of other galaxies...
838
01:00:53,851 --> 01:00:59,423
a structure that reaches
to the very edge of the universe.
839
01:01:05,396 --> 01:01:08,232
We've left our home galaxy
to take the earth
840
01:01:08,265 --> 01:01:13,170
across billions of light years
of space and time.
841
01:01:18,576 --> 01:01:19,777
BULLOCK: One of the great things
about telescopes
842
01:01:19,810 --> 01:01:22,413
is they're time machines.
843
01:01:22,446 --> 01:01:24,882
Because light travels at a finite speed,
844
01:01:24,915 --> 01:01:26,517
when we look at distant objects
845
01:01:26,550 --> 01:01:30,521
we see them as they were
when the light left them.
846
01:01:30,554 --> 01:01:34,358
NARRATOR: As astronomers look back
over billions of years,
847
01:01:34,392 --> 01:01:38,162
they see a universe
teeming with galaxies.
848
01:01:41,465 --> 01:01:46,771
But these galaxies aren't scattered
randomly through space.
849
01:01:49,273 --> 01:01:58,048
They cluster along delicate filaments
woven in an intricate structure...
850
01:01:58,082 --> 01:02:01,118
a vast cosmic web
that holds the answer
851
01:02:01,152 --> 01:02:05,122
to the birth of galaxies
themselves.
852
01:02:09,627 --> 01:02:14,098
It's a story shrouded
in darkness.
853
01:02:14,131 --> 01:02:22,006
Look back far enough and gradually
all the galaxies disappear.
854
01:02:22,039 --> 01:02:25,509
We've reached a mysterious
period of time,
855
01:02:25,543 --> 01:02:29,346
12.5 billion years ago.
856
01:02:29,380 --> 01:02:31,682
BULLOCK: There's this time period
that we can't see
857
01:02:31,715 --> 01:02:33,384
because nothing's formed yet.
858
01:02:33,417 --> 01:02:37,154
It's this epoch that's called
the dark ages.
859
01:02:40,090 --> 01:02:44,128
NARRATOR: During the dark ages,
the universe was a very different place
860
01:02:44,161 --> 01:02:47,097
than the one we live in today.
861
01:02:49,700 --> 01:02:53,737
It's filled with dense clouds
of hydrogen gas.
862
01:02:56,006 --> 01:02:59,910
Just as gas obscures stars
in the Milky Way today,
863
01:02:59,944 --> 01:03:06,417
these clouds of hydrogen block the view
inside the early universe.
864
01:03:06,450 --> 01:03:09,553
BULLOCK: It's extremely frustrating
because this region,
865
01:03:09,587 --> 01:03:13,057
this time period, holds within it,
in some sense,
866
01:03:13,090 --> 01:03:16,727
the Rosetta Stone
of galaxy formation.
867
01:03:16,760 --> 01:03:19,296
NARRATOR: But there is one clue
to what's happening
868
01:03:19,330 --> 01:03:24,134
inside those dense
hydrogen clouds.
869
01:03:24,168 --> 01:03:26,003
Look back further in time
870
01:03:26,036 --> 01:03:31,842
to a moment just 380,000 years
after the big bang.
871
01:03:31,876 --> 01:03:35,212
The universe isn't filled
with darkness...
872
01:03:38,549 --> 01:03:41,452
but with light.
873
01:03:41,485 --> 01:03:46,357
Its faint afterglow is still visible
to astronomers today.
874
01:03:48,826 --> 01:03:50,027
BULLOCK: In fact,
this picture is amazing.
875
01:03:50,060 --> 01:03:52,429
This is a picture
of the early universe.
876
01:03:52,463 --> 01:03:57,535
This is an image of the afterglow
of the big bang.
877
01:03:57,568 --> 01:04:01,205
NARRATOR: The universe is filled
with a hot atmosphere
878
01:04:01,238 --> 01:04:04,041
of matter and radiation.
879
01:04:06,477 --> 01:04:10,981
But already the seeds of change
are being sown.
880
01:04:15,753 --> 01:04:17,454
BULLOCK: Everywhere we look
around us in the universe
881
01:04:17,488 --> 01:04:20,858
we see structure; we see galaxies
all over the place.
882
01:04:20,891 --> 01:04:22,726
Where do these galaxies
come from?
883
01:04:22,760 --> 01:04:25,829
There's a big clue to this
buried in this picture.
884
01:04:25,863 --> 01:04:27,498
If you look closely,
you can see
885
01:04:27,531 --> 01:04:30,334
that there are red spots
and there are blue spots.
886
01:04:30,367 --> 01:04:34,471
These red regions are regions
where there's basically more stuff,
887
01:04:34,505 --> 01:04:39,109
and the blue regions are the regions
where there's less stuff.
888
01:04:39,143 --> 01:04:41,912
NARRATOR: This image reveals
tiny variations
889
01:04:41,946 --> 01:04:46,650
in the density of the gas
that fills the early universe.
890
01:04:49,119 --> 01:04:53,157
Minute ripples
that will grow with time.
891
01:04:55,392 --> 01:04:58,896
BULLOCK: We think that these ripples,
these primordial ripples,
892
01:04:58,929 --> 01:05:01,799
are the seeds
to all future structure.
893
01:05:01,832 --> 01:05:06,103
These ripples eventually grew
into what became the first galaxies.
894
01:05:06,136 --> 01:05:08,072
NARRATOR: It takes
a powerful force
895
01:05:08,105 --> 01:05:12,543
to grow something so small
into something so big.
896
01:05:12,576 --> 01:05:15,379
BULLOCK: It's gravity
that amplifies these ripples,
897
01:05:15,412 --> 01:05:19,550
and in fact we need
an additional source of gravity
898
01:05:19,583 --> 01:05:23,253
to amplify those ripples to form
galaxies like we see today,
899
01:05:23,287 --> 01:05:26,690
and that additional gravity comes
in the form of dark matter.
900
01:05:29,860 --> 01:05:34,198
PRIMACK: What happens is that first
the dark matter forms the structure.
901
01:05:34,231 --> 01:05:37,568
The ordinary matter
then follows the dark matter.
902
01:05:37,601 --> 01:05:40,604
The ordinary matter is hydrogen
and helium at this stage.
903
01:05:40,638 --> 01:05:44,608
And the hydrogen and helium
fall to the center
904
01:05:44,642 --> 01:05:47,277
of the dark matter halos
that are forming,
905
01:05:47,311 --> 01:05:51,515
and that's going to become
the galaxies.
906
01:05:51,548 --> 01:05:53,784
NARRATOR: Dark matter may be
the missing link
907
01:05:53,817 --> 01:05:57,688
between these minute ripples
in the early universe
908
01:05:57,721 --> 01:06:02,493
and the vast cosmic web
that now fills space.
909
01:06:08,098 --> 01:06:11,969
But dark matter is invisible.
910
01:06:13,203 --> 01:06:18,442
So there's no way to actually see it
creating the cosmic web.
911
01:06:20,511 --> 01:06:22,646
But the process can be simulated
912
01:06:22,680 --> 01:06:27,151
in one of the world's
most powerful super computers.
913
01:06:30,454 --> 01:06:33,891
PRIMACK: Here we are at NASA Ames,
914
01:06:33,924 --> 01:06:39,663
the research center where we have
the Pleiades super computer.
915
01:06:39,697 --> 01:06:45,069
Each one of these cabinets
contains 512 processors.
916
01:06:45,102 --> 01:06:48,706
Let me show you.
917
01:06:48,739 --> 01:06:52,676
So that's half a terabyte
in each one of these cabinets.
918
01:06:52,710 --> 01:06:54,745
There's 110 of these cabinets
919
01:06:54,778 --> 01:06:58,716
to make up the entire
Pleiades super computer.
920
01:06:58,749 --> 01:07:00,918
So this is a really big
super computer.
921
01:07:00,951 --> 01:07:03,020
This is NASA's biggest.
922
01:07:05,222 --> 01:07:07,324
NARRATOR: The challenge
is equally big...
923
01:07:07,357 --> 01:07:09,793
to develop a virtual universe...
924
01:07:09,827 --> 01:07:13,897
from its early beginnings
all the way to the present day...
925
01:07:13,931 --> 01:07:21,038
to see what role dark matter might
have played in shaping the cosmos.
926
01:07:21,071 --> 01:07:24,341
If you tried to do this
on a home computer,
927
01:07:24,374 --> 01:07:27,611
it would take over 680 years.
928
01:07:29,480 --> 01:07:31,215
PRIMACK: If we're doing
our job right,
929
01:07:31,248 --> 01:07:35,252
we can put the pictures
into a video, if you like,
930
01:07:35,285 --> 01:07:39,022
that shows the whole structure
of the universe.
931
01:07:39,056 --> 01:07:42,092
NARRATOR: And this is the end result.
932
01:07:42,126 --> 01:07:44,261
It's called Bolshoi...
933
01:07:44,294 --> 01:07:46,830
an amazing visualization
934
01:07:46,864 --> 01:07:49,900
of what the structure
of dark matter might look like
935
01:07:49,933 --> 01:07:52,369
in the universe today.
936
01:07:56,206 --> 01:07:57,708
PRIMACK: So what we're looking at
937
01:07:57,741 --> 01:08:03,247
is a region about 200 million
light years across,
938
01:08:03,280 --> 01:08:06,750
which is actually just a small part
of our really big simulation
939
01:08:06,784 --> 01:08:09,920
that we call Bolshoi,
which is Russian for "big."
940
01:08:09,953 --> 01:08:13,357
Everything that you see here
is actually completely invisible.
941
01:08:13,390 --> 01:08:17,327
It's not the visible universe
that you're seeing.
942
01:08:17,361 --> 01:08:20,664
The bright spots are dark matter.
943
01:08:20,697 --> 01:08:26,770
They're the halos of dark matter
within which galaxies form.
944
01:08:26,804 --> 01:08:32,075
And each one of these little blobs
would represent probably one,
945
01:08:32,109 --> 01:08:36,246
or at most a couple
of Milky Way size galaxies.
946
01:08:36,280 --> 01:08:42,586
And you can see that the galaxies
are in long chains,
947
01:08:42,619 --> 01:08:44,888
filaments we call them.
948
01:08:44,922 --> 01:08:51,395
Basically all the structure is forming
along these filaments of dark matter.
949
01:08:54,131 --> 01:08:57,367
NARRATOR: Now comes
the real test of success:
950
01:08:57,401 --> 01:09:00,704
Primack compares
the Bolshoi predictions
951
01:09:00,737 --> 01:09:06,743
with the actual structure of galaxies
scientists see in the universe.
952
01:09:06,777 --> 01:09:08,412
PRIMACK: As far as we can tell,
953
01:09:08,445 --> 01:09:11,949
these simulated universes
that we make in the super computers
954
01:09:11,982 --> 01:09:14,284
look just like the observed universe.
955
01:09:14,318 --> 01:09:16,687
There don't seem to be
any discrepancies at all.
956
01:09:16,720 --> 01:09:20,123
This is exactly the way
we see the galaxies distributed
957
01:09:20,157 --> 01:09:23,927
in the observed universe.
958
01:09:23,961 --> 01:09:28,799
NARRATOR: The Bolshoi simulations
are astounding.
959
01:09:28,832 --> 01:09:34,705
They match the pattern of galaxies
seen in the cosmos today perfectly.
960
01:09:37,875 --> 01:09:39,509
It's persuasive evidence
961
01:09:39,543 --> 01:09:45,616
that dark matter has been sculpting
the universe for billions of years.
962
01:09:49,853 --> 01:09:51,588
PRIMACK: No, I'm really
impressed with this
963
01:09:51,622 --> 01:09:53,523
because we stuck
our necks way out
964
01:09:53,557 --> 01:09:56,693
when we made
these first predictions,
965
01:09:56,727 --> 01:09:59,363
and they turned out to be right.
966
01:09:59,396 --> 01:10:01,765
And they keep turning out
to be right.
967
01:10:01,798 --> 01:10:05,535
And, you know, this is, of course,
great joy for a theorist.
968
01:10:07,704 --> 01:10:11,208
NARRATOR: By going back
to the beginning of the universe,
969
01:10:11,241 --> 01:10:13,777
astronomers
have uncovered the origin
970
01:10:13,810 --> 01:10:19,383
of the underlying structure
of the entire cosmos.
971
01:10:19,416 --> 01:10:23,553
But our time travel
is far from over.
972
01:10:23,587 --> 01:10:30,661
The question of how the first galaxies
kindled the very first stars still remains.
973
01:10:34,197 --> 01:10:39,970
We're taking the earth
inside the dark age...
974
01:10:40,003 --> 01:10:44,107
a time over 12.5 billion years ago.
975
01:10:44,141 --> 01:10:48,612
The sight is spectacular.
976
01:10:48,645 --> 01:10:53,750
Our skies are lit by the first stars
of the Milky Way.
977
01:10:56,353 --> 01:11:00,257
Their light pierces the hydrogen fog...
978
01:11:00,290 --> 01:11:05,362
bathing the earth in strong
ultraviolet energy.
979
01:11:05,395 --> 01:11:12,569
These first stars will change the way
we see the universe forever.
980
01:11:12,602 --> 01:11:17,040
Tom Abel studies the life and death
of these early stars.
981
01:11:19,910 --> 01:11:22,879
TOM ABEL: The beautiful thing
is that we now have computers.
982
01:11:22,913 --> 01:11:25,449
We program them
with the laws of physics,
983
01:11:25,482 --> 01:11:27,584
put in some gravity,
hydrodynamics,
984
01:11:27,617 --> 01:11:30,253
how gases move around,
some of the chemistry,
985
01:11:30,287 --> 01:11:33,023
and as we evolve it
all together,
986
01:11:33,056 --> 01:11:36,226
we gain an intuition
of how stars come about,
987
01:11:36,259 --> 01:11:41,431
and in the case of the very first stars,
this is absolutely crucial.
988
01:11:44,101 --> 01:11:46,403
NARRATOR: Abel begins
with the basic ingredients
989
01:11:46,436 --> 01:11:49,940
available during the dark ages:
990
01:11:49,973 --> 01:11:54,845
hydrogen, helium,
dark matter and gravity.
991
01:11:56,847 --> 01:11:58,782
Using computer models,
992
01:11:58,815 --> 01:12:03,320
Abel recreates the lives
of these early stars.
993
01:12:08,558 --> 01:12:11,361
ABEL: Here we see one of
the first stars in the universe.
994
01:12:11,395 --> 01:12:13,663
It's a hundred times
as massive as the sun,
995
01:12:13,697 --> 01:12:17,167
a million times as bright.
996
01:12:17,200 --> 01:12:20,904
NARRATOR: The first stars are huge...
997
01:12:20,937 --> 01:12:24,374
swollen by the massive amounts
of hydrogen gas
998
01:12:24,408 --> 01:12:29,513
pulled in by the gravitational force
of dark matter.
999
01:12:29,546 --> 01:12:31,681
ABEL: And so even though
they have all this fuel to burn
1000
01:12:31,715 --> 01:12:33,483
you'd think they could live
for a long time.
1001
01:12:33,517 --> 01:12:35,852
They run through it so quickly
1002
01:12:35,886 --> 01:12:41,792
that even after a few million years
they're already dead.
1003
01:12:41,825 --> 01:12:43,827
NARRATOR: The first stars
in our Milky Way
1004
01:12:43,860 --> 01:12:47,164
are fierce, high octane stars...
1005
01:12:47,197 --> 01:12:51,535
burning their hydrogen fuel
at tremendous rates...
1006
01:12:51,568 --> 01:12:55,138
racing through their life cycle.
1007
01:12:55,172 --> 01:12:56,606
ABEL: They're like the rock stars.
1008
01:12:56,640 --> 01:12:58,275
They live fast and die young.
1009
01:12:58,308 --> 01:13:00,143
They run through
their fuel very quickly
1010
01:13:00,177 --> 01:13:04,247
and even after just a few million years
they already die.
1011
01:13:04,281 --> 01:13:07,517
NARRATOR: They die in some
of the most violent explosions
1012
01:13:07,551 --> 01:13:11,421
ever to rock the universe...
1013
01:13:11,455 --> 01:13:15,292
gigantic supernovas
that shine brilliantly.
1014
01:13:19,362 --> 01:13:20,730
The energy given off
1015
01:13:20,764 --> 01:13:24,201
during the life and death
of these massive stars
1016
01:13:24,234 --> 01:13:27,904
leads to a miraculous transformation.
1017
01:13:31,508 --> 01:13:34,578
ABEL: In the first billion years
of the universe's history,
1018
01:13:34,611 --> 01:13:38,715
galaxies start to form
in a dark hydrogen fog,
1019
01:13:38,748 --> 01:13:42,119
their light not being able
to get to us.
1020
01:13:42,152 --> 01:13:43,687
But as time progresses
1021
01:13:43,720 --> 01:13:47,657
and their most massive stars
put out ultraviolet radiation,
1022
01:13:47,691 --> 01:13:51,394
it's that radiation itself
that changes the fog around them,
1023
01:13:51,428 --> 01:13:54,231
and the universe becomes
transparent in those regions.
1024
01:13:54,264 --> 01:13:59,503
These galaxies in here are clearing out
the fog around them.
1025
01:13:59,536 --> 01:14:03,406
NARRATOR: The blue voids
are where energy from the new stars
1026
01:14:03,440 --> 01:14:07,043
is clearing the dark hydrogen fog.
1027
01:14:11,915 --> 01:14:14,484
ABEL: But towards a billion years
after the big bang
1028
01:14:14,518 --> 01:14:16,219
the entire fog has cleared
1029
01:14:16,253 --> 01:14:19,356
and we now see all the galaxies,
1030
01:14:19,389 --> 01:14:22,325
and the dark ages end.
1031
01:14:25,128 --> 01:14:27,430
NARRATOR: As the hydrogen fog lifts,
1032
01:14:27,464 --> 01:14:33,203
we get our first glimpse
of newborn galaxies...
1033
01:14:33,236 --> 01:14:37,741
including our very own Milky Way.
1034
01:14:52,289 --> 01:14:55,458
RICHARD ELLIS: This remarkable image
is the Hubble ultra deep field.
1035
01:14:55,492 --> 01:14:58,028
It's the longest exposure
that's ever been taken
1036
01:14:58,061 --> 01:14:59,829
with the Hubble Space Telescope.
1037
01:14:59,863 --> 01:15:01,464
It's a truly remarkable image,
1038
01:15:01,498 --> 01:15:06,036
probably the most famous
to professional astronomers.
1039
01:15:06,069 --> 01:15:11,474
NARRATOR: For over eleven days
Hubble pointed at a tiny patch of sky
1040
01:15:11,508 --> 01:15:15,812
about the width of a dime
held 75 feet away.
1041
01:15:20,050 --> 01:15:23,887
Every faint smudge of light is a galaxy.
1042
01:15:27,791 --> 01:15:31,494
For Richard Ellis,
it's a treasure trove.
1043
01:15:32,929 --> 01:15:35,999
ELLIS: So much like an archaeologist
would piece together history
1044
01:15:36,032 --> 01:15:38,868
by digging into deeper
and deeper layers,
1045
01:15:38,902 --> 01:15:42,205
so a cosmologist like myself
uses this image
1046
01:15:42,239 --> 01:15:44,007
to look at the history of the universe,
1047
01:15:44,040 --> 01:15:47,877
how the most distant galaxies,
seen as they were a long time ago,
1048
01:15:47,911 --> 01:15:53,450
evolve and grow to the bigger systems
that we see around us today.
1049
01:15:53,483 --> 01:15:59,489
NARRATOR: This image gives us
a sense of the dawn of our Milky Way.
1050
01:15:59,522 --> 01:16:01,725
ELLIS: When we look
at these early galaxies,
1051
01:16:01,758 --> 01:16:05,795
they don't resemble the star cities
that we see today.
1052
01:16:05,829 --> 01:16:07,664
They're lumpy, they're irregular,
1053
01:16:07,697 --> 01:16:10,634
they appear to be interacting
with their neighbors,
1054
01:16:10,667 --> 01:16:12,602
they're physically very, very small.
1055
01:16:12,636 --> 01:16:17,607
So clearly the universe was
very different in those early times.
1056
01:16:17,641 --> 01:16:23,413
NARRATOR: 12 billion years ago
the universe is a much smaller place.
1057
01:16:23,446 --> 01:16:27,284
It hasn't yet expanded
to the size it is today.
1058
01:16:29,853 --> 01:16:35,358
Our young Milky Way
is jostling for room.
1059
01:16:35,392 --> 01:16:37,527
ELLIS: So it's very difficult
for these early galaxies
1060
01:16:37,560 --> 01:16:39,362
to establish themselves.
1061
01:16:39,396 --> 01:16:45,935
These early galaxies are struggling
to survive at this very early time.
1062
01:16:47,203 --> 01:16:50,473
NARRATOR: It's survival of the fittest...
1063
01:16:50,507 --> 01:16:55,612
the largest galaxies grow bigger
by devouring the smallest.
1064
01:16:57,814 --> 01:16:59,849
ELLIS: So it's tough
for these early systems to form,
1065
01:16:59,883 --> 01:17:03,353
but clearly they do, and they eventually
merge with their neighbors
1066
01:17:03,386 --> 01:17:06,222
and form the bigger systems
that we see today.
1067
01:17:09,693 --> 01:17:11,828
NARRATOR: These collisions
in the early universe
1068
01:17:11,861 --> 01:17:17,334
created the beautiful spiral galaxy
we live in today...
1069
01:17:19,803 --> 01:17:22,339
...and they've never stopped.
1070
01:17:22,372 --> 01:17:25,241
Astronomers believe
there's still one final collision
1071
01:17:25,275 --> 01:17:28,211
in store for the Milky Way.
1072
01:17:28,244 --> 01:17:31,881
One that will change it forever.
1073
01:17:44,761 --> 01:17:51,534
We've transported the earth
three billion years into the future.
1074
01:17:51,568 --> 01:17:57,407
The sky is dominated by
a massive galaxy called Andromeda.
1075
01:17:59,976 --> 01:18:03,146
The view may look peaceful,
1076
01:18:03,179 --> 01:18:05,982
but one of the greatest calamities
in the universe
1077
01:18:06,015 --> 01:18:08,251
is about to take place...
1078
01:18:10,587 --> 01:18:16,593
...and clues to the impending disaster
lie in these mysterious Hubble images.
1079
01:18:18,361 --> 01:18:22,699
Galaxies unlike any other...
1080
01:18:22,732 --> 01:18:24,501
distorted...
1081
01:18:26,836 --> 01:18:30,006
deformed.
1082
01:18:30,039 --> 01:18:32,942
Astronomers rely
on computers for help
1083
01:18:32,976 --> 01:18:37,480
in decoding what these
mysterious objects represent.
1084
01:18:39,549 --> 01:18:42,919
PRIMACK: What we do is
we make galaxies
1085
01:18:42,952 --> 01:18:46,890
that look just like the Milky Way
and similar galaxies.
1086
01:18:46,923 --> 01:18:49,993
And we let them evolve
in the computer,
1087
01:18:50,026 --> 01:18:52,128
they develop
the spiral structure,
1088
01:18:52,162 --> 01:18:54,664
they look quite realistic.
1089
01:18:54,697 --> 01:19:00,603
We then put them
on a collision path.
1090
01:19:00,637 --> 01:19:02,972
NARRATOR: Freeze frame
these simulations
1091
01:19:03,006 --> 01:19:05,041
and match them with real images
1092
01:19:05,074 --> 01:19:10,647
and suddenly the picture
becomes clear:
1093
01:19:10,680 --> 01:19:16,519
It's the greatest clash
in the cosmos...
1094
01:19:16,553 --> 01:19:19,422
galaxies in collision.
1095
01:19:23,960 --> 01:19:28,198
Like cities, galaxies
tend to cluster.
1096
01:19:28,231 --> 01:19:30,500
Our Milky Way
belongs to a cluster
1097
01:19:30,533 --> 01:19:33,002
called the local group,
1098
01:19:33,036 --> 01:19:36,840
made up of at least 50 galaxies.
1099
01:19:40,343 --> 01:19:43,513
The largest in the pack
is Andromeda...
1100
01:19:43,546 --> 01:19:47,283
a spiral galaxy that's
even bigger than ours.
1101
01:19:49,352 --> 01:19:55,291
Today Andromeda lies
2.5 million light years away.
1102
01:19:55,325 --> 01:20:02,565
But astronomers like Abraham Loeb
believe that distance is closing in.
1103
01:20:02,599 --> 01:20:04,834
ABRAHAM LOEB: When I started
working in astrophysics
1104
01:20:04,868 --> 01:20:07,003
I noticed that most
of my colleagues
1105
01:20:07,036 --> 01:20:10,907
are thinking about other galaxies
interacting with each other,
1106
01:20:10,940 --> 01:20:13,076
colliding with each other,
1107
01:20:13,109 --> 01:20:16,279
and I was wondering why
aren't they examining
1108
01:20:16,312 --> 01:20:20,216
the future of the Milky Way
and the Andromeda Galaxy
1109
01:20:20,250 --> 01:20:23,786
as they will come together.
1110
01:20:23,820 --> 01:20:26,789
NARRATOR: Trouble is brewing
for our star city.
1111
01:20:28,825 --> 01:20:33,263
PRIMACK: Our galaxy is rushing
toward the great galaxy Andromeda,
1112
01:20:33,296 --> 01:20:34,898
they're rushing toward each other,
1113
01:20:34,931 --> 01:20:37,300
and they're going
to encounter each other
1114
01:20:37,333 --> 01:20:40,136
in a couple billion years.
1115
01:20:43,339 --> 01:20:44,941
NARRATOR: Loeb and his colleagues
1116
01:20:44,974 --> 01:20:49,712
decide to simulate this
intergalactic clash of the titans.
1117
01:20:51,681 --> 01:20:56,252
LOEB: This was the first
simulation of its kind.
1118
01:20:56,286 --> 01:20:59,589
Initially the two galaxies
plunge through each other
1119
01:20:59,622 --> 01:21:05,995
producing these beautiful tails of stars,
due to the force of gravity.
1120
01:21:06,029 --> 01:21:09,399
They run away, turn around
and come back together,
1121
01:21:09,432 --> 01:21:11,935
to make one big
spheroid of stars,
1122
01:21:11,968 --> 01:21:15,772
which I called
the Milkomeda Galaxy.
1123
01:21:15,805 --> 01:21:19,208
NARRATOR: When the Milky Way
merges with Andromeda,
1124
01:21:19,242 --> 01:21:23,346
almost one trillion stars
will come together.
1125
01:21:29,252 --> 01:21:30,620
KIRSHNER: The beautiful
spiral structure
1126
01:21:30,653 --> 01:21:32,121
of our Milky Way galaxy
1127
01:21:32,155 --> 01:21:34,290
is not something that's
going to last forever.
1128
01:21:34,324 --> 01:21:38,328
It's going to be a mess,
for a while.
1129
01:21:38,361 --> 01:21:40,396
The collision will not be one
1130
01:21:40,430 --> 01:21:42,432
in which these two things
are destroyed,
1131
01:21:42,465 --> 01:21:45,501
but it is one where the gas
in each system
1132
01:21:45,535 --> 01:21:48,104
will collide with the gas
in the other.
1133
01:21:48,137 --> 01:21:51,808
That it'll have a burst
of star formation.
1134
01:21:51,841 --> 01:21:54,510
LOEB: And the formation
of these new stars
1135
01:21:54,544 --> 01:21:58,982
will mark the rebirth
of a new galaxy.
1136
01:22:03,353 --> 01:22:05,788
NARRATOR: This spectacular
Hubble image
1137
01:22:05,822 --> 01:22:09,525
shows the Antennae Galaxies...
1138
01:22:09,559 --> 01:22:16,666
a grand cosmic collision
between two spiral star cities.
1139
01:22:16,699 --> 01:22:21,437
The galaxies are
in a frenzy of star birth...
1140
01:22:21,471 --> 01:22:27,710
a multitude of nebulas
glow pink in the darkness...
1141
01:22:27,744 --> 01:22:30,847
one final flare of stellar activity
1142
01:22:30,880 --> 01:22:34,517
before the galaxies merge
to become one.
1143
01:22:36,185 --> 01:22:39,722
This is the fate that awaits
our Milky Way
1144
01:22:39,756 --> 01:22:45,028
when it merges with Andromeda
three billion years from now.
1145
01:22:47,597 --> 01:22:48,865
KIRSHNER: When they collide
1146
01:22:48,898 --> 01:22:52,235
there will be a lot of new
star formation that takes place,
1147
01:22:52,268 --> 01:22:56,572
there will be a kind of rejuvenation
of the Milky Way for a little while
1148
01:22:56,606 --> 01:22:59,275
and then eventually
this combined system
1149
01:22:59,308 --> 01:23:01,611
will settle down
to become a new thing,
1150
01:23:01,644 --> 01:23:03,346
probably a bigger galaxy
1151
01:23:03,379 --> 01:23:07,850
than either of the galaxies
out of which it was made.
1152
01:23:07,884 --> 01:23:14,524
NARRATOR: But the real surprise
is the shape of this new galaxy.
1153
01:23:14,557 --> 01:23:16,359
PRIMACK: A new galaxy is formed
1154
01:23:16,392 --> 01:23:20,663
where instead of the discs
that the original galaxies had,
1155
01:23:20,697 --> 01:23:24,067
where all the stars are going around
more or less on a plane,
1156
01:23:24,100 --> 01:23:27,036
instead the stars are going
every which way,
1157
01:23:27,070 --> 01:23:31,674
just like the elliptical galaxies
that we see.
1158
01:23:31,708 --> 01:23:34,277
And so we're pretty sure
that this process
1159
01:23:34,310 --> 01:23:39,716
must be a large part
of how elliptical galaxies form.
1160
01:23:39,749 --> 01:23:42,218
NARRATOR: The collision
of the Milky Way with Andromeda
1161
01:23:42,251 --> 01:23:46,322
will leave behind
a giant elliptical galaxy.
1162
01:23:50,359 --> 01:23:55,164
But before that happens
there'll be one final sight to behold.
1163
01:23:56,699 --> 01:23:59,702
LOEB: The image of Andromeda
will be stretched across the sky,
1164
01:23:59,736 --> 01:24:05,074
looming as big
as the Milky Way itself,
1165
01:24:05,108 --> 01:24:10,046
and it's conceivable that there
would be human beings like ourselves
1166
01:24:10,079 --> 01:24:15,118
looking at the sky and seeing
this spectacular image.
1167
01:24:15,151 --> 01:24:19,922
NARRATOR: We might not be
the only beings enjoying the view.
1168
01:24:19,956 --> 01:24:24,794
Could our galaxy be home
to other civilizations?
1169
01:24:24,827 --> 01:24:30,399
Unknown life yet to be discovered
inside the Milky Way?
1170
01:24:40,676 --> 01:24:46,682
There are around 200 billion stars
in our galaxy.
1171
01:24:46,716 --> 01:24:52,622
But there's only one neighborhood
we know for sure that sustains life:
1172
01:24:57,260 --> 01:25:00,663
Earth.
1173
01:25:00,696 --> 01:25:05,168
GEOFF MARCY: The sun powers almost
everything here on the Earth.
1174
01:25:05,201 --> 01:25:08,070
It's the energy source; it's the engine
1175
01:25:08,104 --> 01:25:10,573
of life and many other processes.
1176
01:25:10,606 --> 01:25:16,312
And life here on Earth
is based heavily on water.
1177
01:25:16,345 --> 01:25:22,251
And it's liquid water that's the key
to life as we know it.
1178
01:25:22,285 --> 01:25:26,222
And it's because liquid water
serves as the solvent,
1179
01:25:26,255 --> 01:25:30,626
the cocktail mixer,
for the biochemistry of life.
1180
01:25:33,429 --> 01:25:36,465
NARRATOR: Earth is the only planet
in our solar system
1181
01:25:36,499 --> 01:25:39,869
with abundant liquid water.
1182
01:25:39,902 --> 01:25:42,138
As with any prime real estate,
1183
01:25:42,171 --> 01:25:46,142
it's all about location,
location, location.
1184
01:25:48,945 --> 01:25:51,180
MARCY: Venus is closer to the sun,
1185
01:25:51,214 --> 01:25:54,517
Mars is farther from the sun,
1186
01:25:54,550 --> 01:25:58,921
and there's a zone in between
the blazing hot furnace of Venus,
1187
01:25:58,955 --> 01:26:00,423
the frigid Mars,
1188
01:26:00,456 --> 01:26:03,359
that zone in between
we call the habitable zone,
1189
01:26:03,392 --> 01:26:05,928
and the Earth lies
smack in that thing,
1190
01:26:05,962 --> 01:26:09,599
where water would be
in liquid form,
1191
01:26:09,632 --> 01:26:14,604
not in steam, too hot,
not in ice form, too cold.
1192
01:26:14,637 --> 01:26:17,773
But rather a temperature that,
as Goldilocks said,
1193
01:26:17,807 --> 01:26:20,276
is just right for life.
1194
01:26:22,879 --> 01:26:25,147
NARRATOR: The location
of a habitable green zone
1195
01:26:25,181 --> 01:26:27,750
depends on the star.
1196
01:26:30,486 --> 01:26:36,092
With hot blue stars,
the green zone is further out.
1197
01:26:36,125 --> 01:26:41,163
With cooler red stars,
it's closer in.
1198
01:26:41,197 --> 01:26:46,602
Every star in the Milky Way
has a habitable zone.
1199
01:26:46,636 --> 01:26:50,740
But not every star has
planets within that zone.
1200
01:26:53,175 --> 01:26:57,647
MARCY: In 1995 something happened
that was extraordinary.
1201
01:26:57,680 --> 01:27:00,483
I got a call from my collaborator,
Paul Butler,
1202
01:27:00,516 --> 01:27:03,753
and all he said was, Geoff,
come over here.
1203
01:27:03,786 --> 01:27:07,790
And it was a moment
that I will never forget.
1204
01:27:07,823 --> 01:27:11,928
I was silent, Paul was silent,
and we were just stunned.
1205
01:27:11,961 --> 01:27:13,896
There on the computer screen
1206
01:27:13,930 --> 01:27:19,135
I saw the unmistakable
signature of a planet.
1207
01:27:21,237 --> 01:27:27,543
NARRATOR: Marcy had discovered
the first planet around another star.
1208
01:27:27,576 --> 01:27:29,812
But he couldn't actually see it
1209
01:27:29,845 --> 01:27:33,549
because the planet
was too small and dim.
1210
01:27:37,219 --> 01:27:42,892
MARCY: Any planet orbiting a star
is lost in the glare of that host star,
1211
01:27:42,925 --> 01:27:46,162
that outshines it
by a factor of a billion.
1212
01:27:46,195 --> 01:27:51,067
And so instead, to detect planets,
we watch the stars.
1213
01:27:51,100 --> 01:27:54,537
And in fact a star
will wobble in space
1214
01:27:54,570 --> 01:27:58,507
because it's yanked on
gravitationally by the planet,
1215
01:27:58,541 --> 01:28:01,377
or planets, orbiting that star.
1216
01:28:01,410 --> 01:28:03,446
And by watching the star alone
1217
01:28:03,479 --> 01:28:06,515
we can determine whether
the star has planets
1218
01:28:06,549 --> 01:28:10,820
and how far out those planets are
from the host star.
1219
01:28:12,722 --> 01:28:16,759
NARRATOR: So far astronomers
have found over 400 planets
1220
01:28:16,792 --> 01:28:19,495
orbiting stars in our galaxy.
1221
01:28:19,528 --> 01:28:23,733
But none of them seem to be
in habitable zones.
1222
01:28:23,766 --> 01:28:28,104
MARCY: One type of giant planet
orbits very close to its star.
1223
01:28:28,137 --> 01:28:29,605
We call them hot Jupiters,
1224
01:28:29,638 --> 01:28:32,508
because these Jupiter-like planets
are so close
1225
01:28:32,541 --> 01:28:38,681
that they're blow-torched
by the intense heat from the star.
1226
01:28:38,714 --> 01:28:42,218
The other sort of planet
we've found is also bizarre.
1227
01:28:42,251 --> 01:28:46,222
We've found planets that orbit
in elongated orbits,
1228
01:28:46,255 --> 01:28:48,657
elliptical, stretched out orbits,
1229
01:28:48,691 --> 01:28:50,760
but then the planets
go very far from the star
1230
01:28:50,793 --> 01:28:54,497
where they would be quite cold.
1231
01:28:54,530 --> 01:28:57,266
And so the planets
that we've found so far
1232
01:28:57,299 --> 01:29:00,536
are a little too weird
for us to imagine
1233
01:29:00,569 --> 01:29:04,573
that life would have
a good chance of surviving.
1234
01:29:04,607 --> 01:29:06,008
MAN: Power on.
1235
01:29:06,042 --> 01:29:07,276
External.
1236
01:29:07,309 --> 01:29:12,148
NARRATOR: But all that may be
about to change.
1237
01:29:12,181 --> 01:29:18,354
Recently NASA launched
a powerful new telescope called Kepler,
1238
01:29:18,387 --> 01:29:20,389
to hunt for Earth-sized planets
1239
01:29:20,423 --> 01:29:24,760
that may orbit habitable zones
around nearby stars.
1240
01:29:27,496 --> 01:29:30,766
MARCY: Kepler works
in the most simple way.
1241
01:29:30,800 --> 01:29:36,105
All Kepler does is monitor
the brightness of 100,000 stars
1242
01:29:36,138 --> 01:29:38,707
with such exquisite precision
1243
01:29:38,741 --> 01:29:42,511
that it would detect a planet
as small as an Earth-like one
1244
01:29:42,545 --> 01:29:45,948
as it blocks the starlight.
1245
01:29:45,981 --> 01:29:47,683
NARRATOR: We see
the same thing from Earth
1246
01:29:47,716 --> 01:29:52,054
when Venus and Mercury
are silhouetted against the sun.
1247
01:29:55,157 --> 01:29:59,028
But Kepler's task is far more difficult.
1248
01:30:01,163 --> 01:30:03,933
MARCY: It's a little bit like
having a searchlight
1249
01:30:03,966 --> 01:30:07,436
in which you're trying to detect
any dust on that searchlight
1250
01:30:07,470 --> 01:30:09,672
by noticing a dimming
of the searchlight
1251
01:30:09,705 --> 01:30:14,977
when one dust particle falls
on this massive searchlight.
1252
01:30:15,010 --> 01:30:16,545
NARRATOR: From this tiny dimming,
1253
01:30:16,579 --> 01:30:20,649
the size of the planet
can be measured.
1254
01:30:20,683 --> 01:30:25,121
And together with the way it
causes its host star to wobble,
1255
01:30:25,154 --> 01:30:28,057
Marcy can work out its density.
1256
01:30:29,525 --> 01:30:31,427
MARCY: And of course
this is glorious
1257
01:30:31,460 --> 01:30:33,762
because by these measurements
1258
01:30:33,796 --> 01:30:36,565
we'll be able to distinguish
gaseous planets,
1259
01:30:36,599 --> 01:30:38,868
probably not suitable for life,
1260
01:30:38,901 --> 01:30:44,573
from the rocky planets that may have
a surface covered by liquid water.
1261
01:30:46,208 --> 01:30:51,113
NARRATOR: Astronomers aren't sure
how many planets Kepler will find...
1262
01:30:51,147 --> 01:30:54,917
but with 200 billion stars
in the Milky Way,
1263
01:30:54,950 --> 01:30:59,321
the odds look promising.
1264
01:30:59,355 --> 01:31:03,325
Seth Shostak has done the math.
1265
01:31:03,359 --> 01:31:04,860
SETH SHOSTAK: You know,
the indications are
1266
01:31:04,894 --> 01:31:07,263
a lot of those stars have planets,
may be half of them do.
1267
01:31:07,296 --> 01:31:09,465
And since planets, you know,
being like kittens,
1268
01:31:09,498 --> 01:31:11,567
you don't just get one,
you get a couple.
1269
01:31:11,600 --> 01:31:15,738
There are probably on the order
of a million million planets out there.
1270
01:31:18,407 --> 01:31:20,342
NARRATOR: A trillion planets.
1271
01:31:20,376 --> 01:31:24,346
It's an unimaginably vast number.
1272
01:31:24,380 --> 01:31:26,949
But what are the chances
of them being in a location
1273
01:31:26,982 --> 01:31:30,819
where life can flourish?
1274
01:31:30,853 --> 01:31:35,224
MARCY: We can expand the idea
of a habitable zone around a star
1275
01:31:35,257 --> 01:31:40,863
to a habitable zone within
our entire Milky Way galaxy.
1276
01:31:42,064 --> 01:31:44,300
NARRATOR: The search for life begins
1277
01:31:44,333 --> 01:31:48,370
with the search
for a galactic habitable zone,
1278
01:31:48,404 --> 01:31:52,107
the safe haven that
allows life to flourish.
1279
01:31:53,876 --> 01:31:57,613
MARCY: In close, at the hub
there is an extraordinary amount
1280
01:31:57,646 --> 01:32:01,817
of X-rays, harsh radio waves,
even gamma rays
1281
01:32:01,850 --> 01:32:06,488
that would certainly destroy
fragile single-celled life
1282
01:32:06,522 --> 01:32:11,460
just getting a start
toward evolution.
1283
01:32:11,493 --> 01:32:13,662
SHOSTAK: Downtown is dangerous.
1284
01:32:13,696 --> 01:32:15,764
There's a super massive
black hole down there.
1285
01:32:15,798 --> 01:32:20,302
You get too close to that, all sorts
of bad things can happen.
1286
01:32:20,336 --> 01:32:21,770
There are also a lot
of stars down there
1287
01:32:21,804 --> 01:32:23,706
and, you know, a lot of stars
sounds good,
1288
01:32:23,739 --> 01:32:26,809
but on the other hand
if you have too many nearby stars
1289
01:32:26,842 --> 01:32:31,714
they tend to shake up all the comets
in your solar system
1290
01:32:31,747 --> 01:32:33,115
that are constantly
pummeling you
1291
01:32:33,148 --> 01:32:35,985
with these collisions that,
just ask the dinosaurs,
1292
01:32:36,018 --> 01:32:39,088
are not always good for you.
1293
01:32:39,121 --> 01:32:40,856
NARRATOR: The spiral arms may offer
1294
01:32:40,889 --> 01:32:44,560
the safest neighborhoods
in the galaxy.
1295
01:32:44,593 --> 01:32:48,964
But even here, danger
may lurk around the corner.
1296
01:32:50,332 --> 01:32:52,801
SHOSTAK: If you happen to be
on a planet near a supernova,
1297
01:32:52,835 --> 01:32:55,838
that explosion could ruin
your whole day.
1298
01:32:55,871 --> 01:32:57,906
Life might get started,
and then, you know,
1299
01:32:57,940 --> 01:33:01,844
another couple of hundred
million years later it gets wiped out.
1300
01:33:01,877 --> 01:33:04,713
So these areas are sort of
no-go zones, no man's land.
1301
01:33:04,747 --> 01:33:07,583
Well, no alien's land, perhaps.
1302
01:33:07,616 --> 01:33:11,720
NARRATOR: The outer reaches
of our Milky Way are quieter.
1303
01:33:11,754 --> 01:33:16,625
But here life would still
find it difficult to take root.
1304
01:33:16,659 --> 01:33:19,728
MARCY: At the outskirts
of our Milky Way galaxy
1305
01:33:19,762 --> 01:33:21,664
there aren't very many
heavy elements
1306
01:33:21,697 --> 01:33:24,867
of which the cells of our bodies
and life as we know it
1307
01:33:24,900 --> 01:33:26,068
are composed.
1308
01:33:26,101 --> 01:33:29,838
And so we may not have
the essential building blocks of life
1309
01:33:29,872 --> 01:33:33,642
at the outer edges
of our own Milky Way.
1310
01:33:36,412 --> 01:33:41,116
NARRATOR: So it's not an accident
that we are where we are.
1311
01:33:41,150 --> 01:33:45,454
Our neighborhood, tucked away
between two spiral arms,
1312
01:33:45,487 --> 01:33:48,223
is prime real estate.
1313
01:33:48,257 --> 01:33:53,462
It's remained relatively unchanged
for billions of years,
1314
01:33:53,495 --> 01:33:58,467
giving life time
to establish and evolve.
1315
01:34:02,604 --> 01:34:06,141
Other advanced civilizations,
if they exist,
1316
01:34:06,175 --> 01:34:09,445
are likely to live
in similar neighborhoods,
1317
01:34:09,478 --> 01:34:12,948
cocooned from the dangers
of the galaxy.
1318
01:34:15,784 --> 01:34:19,021
We haven't found them yet.
1319
01:34:19,054 --> 01:34:23,826
But then again,
our galaxy's a big place.
1320
01:34:26,195 --> 01:34:27,863
SHOSTAK: We haven't found
any life elsewhere,
1321
01:34:27,896 --> 01:34:29,198
we haven't found pond scum,
1322
01:34:29,231 --> 01:34:31,300
we haven't found
dead pond scum anywhere else,
1323
01:34:31,333 --> 01:34:33,802
not convincingly,
and why is that?
1324
01:34:33,836 --> 01:34:37,106
Well, fewer than a thousand stars
have been looked at carefully
1325
01:34:37,139 --> 01:34:39,675
for planets that might have
intelligent life.
1326
01:34:39,708 --> 01:34:42,745
So you know, it's sort of
like going to Africa
1327
01:34:42,778 --> 01:34:45,948
looking for mega fauna, you know,
elephants, giraffes, something like that,
1328
01:34:45,981 --> 01:34:47,683
and you land in Africa
1329
01:34:47,716 --> 01:34:50,285
and you look at the first
square yard of real estate there
1330
01:34:50,319 --> 01:34:52,621
and you say no elephants here,
then you give up.
1331
01:34:52,654 --> 01:34:55,758
Well, we shouldn't give up,
we're just beginning.
1332
01:34:55,791 --> 01:35:00,729
MARCY: Well, if we do find life,
1333
01:35:00,763 --> 01:35:07,603
it's amazing, if we find life
elsewhere in the universe,
1334
01:35:07,636 --> 01:35:12,841
I think the stock market
won't budge one bit.
1335
01:35:12,875 --> 01:35:17,546
But we humans will know,
for the first time in human history,
1336
01:35:17,579 --> 01:35:20,015
that we're not alone.
1337
01:35:20,048 --> 01:35:24,119
That we have kindred spirits
out among the stars,
1338
01:35:24,153 --> 01:35:29,458
and that our destiny may well be
to venture to the stars,
1339
01:35:29,491 --> 01:35:31,326
communicate with them
1340
01:35:31,360 --> 01:35:36,131
and become members
of a great galactic country club.
109461
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