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NARRATOR:
The Milky Way, our home,

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00:00:06,400 --> 00:00:10,100
{\an1}formed not long after
the Big Bang.

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00:00:10,133 --> 00:00:14,866
{\an1}One of trillions in the
universe.

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00:00:14,900 --> 00:00:17,133
{\an1}This is our galaxy.

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00:00:17,166 --> 00:00:19,933
♪ ♪

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{\an1}Billions of planets orbiting
billions of stars.

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{\an1}We are only just beginning
to understand its true place

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00:00:29,500 --> 00:00:32,333
in the universe.

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GERRY GILMORE:
It was only a hundred years ago,

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{\an1}people thought our Milky Way
was the entire universe.

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♪ ♪

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PAYEL DAS:
If we really want to understand
where we come from

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{\an1}and how the galaxy was formed,

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00:00:44,100 --> 00:00:46,033
{\an1}we can't just look in our cosmic
sort of backyard.

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00:00:46,066 --> 00:00:47,700
{\an1}We need to look much further
afield.

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NARRATOR:
And when we do,

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{\an1}we discover a universe
in turmoil.

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{\an1}VASILY BELOKUROV:
Our history is made up
of multiple collisions

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and interactions
with our neighbors.

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♪ ♪

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RANA EZZEDDINE:
Our Milky Way is not static.

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{\an1}It is dynamic and it has

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{\an1}such a rich, dynamic history.

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NARRATOR:
And our place in it

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far from secure.

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♪ ♪

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DAVID ROSARIO:
A collision can change
the structure of a galaxy,

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{\an1}reorders the stars,
so you end up with something

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{\an1}that looks different,
that behaves differently.

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NARRATOR:
Now we can see our galaxy's
future and its inevitable end.

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JEN GUPTA:
The Andromeda galaxy
is actually heading towards us

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{\an1}at about 250,000 miles per hour.

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GILMORE:
It will be a really nice sight,
actually.

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{\an1}You know, just watch it coming.

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{\an1}I mean, there's nothing
you can do about it

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except sit back
and enjoy the view.

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♪ ♪

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{\an1}MICHELLE COLLINS:
It's all coming together
to tell us about how we got here

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{\an1}and what our place
in the universe really is.

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♪ ♪

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NARRATOR:
"The Milky Way,"
right now, on "NOVA."

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♪ ♪

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{\an1}♪ See me when I float
like a dove ♪

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{\an1}♪ The skies above are lined
with trees ♪

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{\an1}♪ I'm on my knees,
begging please ♪

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00:02:34,133 --> 00:02:41,066
{\an1}♪ Come and take me away ♪

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♪ ♪

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NARRATOR:
Above us in the night sky,

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{\an1}visible all around the world,

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{\an1}the Milky Way wraps its arms
across the sky,

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{\an1}a band of stars like no other.

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GRANT TREMBLAY:
When the Milky Way
is up overhead,

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{\an1}the skies are so brilliantly
bright that I swear

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{\an1}the, the band of the Milky Way,
the disk of our own galaxy,

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{\an1}quite literally casts a shadow.

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♪ ♪

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COLLINS:
Our Milky Way is this really
incredibly beautiful place.

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{\an1}It's this wonderful collection

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{\an1}of beautiful stars, gas,
and dust that all kind of

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swirls together,

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{\an1}almost like an abstract
painting.

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DAS:
We've been trying

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{\an1}to understand the band of stars
that stretches across

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{\an1}the night sky since the time
of the ancient Greeks.

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♪ ♪

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NIA IMARA:
Humans have been looking up

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at the night sky
since the dawn of time

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{\an1}because we want to know
what's out there.

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NARRATOR:
Because the story of our galaxy

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{\an1}is the story of every one of us.

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GILMORE:
How does it all fit together?

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{\an1}What are we part of?

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{\an1}Can we understand it?

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{\an8}♪ ♪

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NARRATOR:
The Milky Way galaxy
takes its name from the dense

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{\an1}band of stars that we see
from Earth,

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{\an1}when in fact, it's a structure
that entirely surrounds us.

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{\an1}Every star in the sky is part of
it, including our sun.

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♪ ♪

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SOWNAK BOSE:
When looking into the night sky,

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{\an7}you would see this band of stars
stretched across it,

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{\an7}which actually corresponds
to the disk of the Milky Way.

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{\an1}So we actually live
inside the Milky Way.

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♪ ♪

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EZZEDDINE:
Our galaxy is a spiral galaxy.

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{\an1}And we can build up
this picture,

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{\an1}which we have been doing for

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{\an7}hundreds of years so far,
since the first astronomers,

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{\an7}like Galileo, to, to kind of
build up this beautiful picture

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00:05:18,833 --> 00:05:22,100
{\an1}of our Milky Way.

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DAS:
Right in the center,
you have a bulge.

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{\an7}Then you have a pancake-like
structure.

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{\an8}That's the disk,
and that's where we are.

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{\an7}And then further out,
you have a faint halo of stars

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00:05:30,133 --> 00:05:34,666
{\an1}that goes quite far beyond
the disk.

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COLLINS:
It's this beautiful
spiral structure

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00:05:36,833 --> 00:05:40,333
{\an1}of hundreds of billions of stars
all orbiting around

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{\an7}a supermassive black hole right
at the center of the galaxy.

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♪ ♪

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NARRATOR:
The Milky Way's complex
structure has taken

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00:05:48,766 --> 00:05:51,433
{\an1}billions of years to evolve.

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{\an1}And yet, it's one of the most
familiar forms in nature.

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{\an8}So let's start
at the very center,

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{\an7}and in the center, there is
a very old bulge,

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{\an7}contains most of the old stars.

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{\an7}And this is the remnants
of the first stars that formed

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{\an7}in our part of the universe.

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{\an7}Right at the very heart of it,

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there is a
supermassive black hole.

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{\an1}That is the core of the
Milky Way as we know it.

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{\an1}And then around that's
the bulge,

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00:06:28,000 --> 00:06:29,766
{\an1}and then there's this
big bar structure,

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{\an1}mostly old stars,

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{\an1}and that's what drives
the spiral arms.

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{\an1}And so we can then say,
"Where are we in all of this?"

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{\an1}We know pretty well where
the sun is.

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{\an7}And hey presto, one sun,
and it'll be about there,

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{\an7}roughly halfway from the center
to the outer

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{\an7}spiral arm structures, and this
is where the sun lives today.

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NARRATOR:
The Milky Way's elegant spirals

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{\an1}are the signature
of its dynamic history.

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00:06:58,866 --> 00:07:02,966
{\an1}The challenge is how to observe
it and tease out that history

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00:07:03,000 --> 00:07:06,366
{\an1}from our position on the inside.

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00:07:06,400 --> 00:07:08,933
COLLINS:
One of the problems of trying
to study the Milky Way

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00:07:08,966 --> 00:07:11,900
{\an1}from our position here on Earth
is that it's really hard

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00:07:11,933 --> 00:07:14,466
{\an1}to get a sense of what
the galaxy looks like overall.

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00:07:14,500 --> 00:07:16,600
{\an1}So, if we really want to
understand where we come from

128
00:07:16,633 --> 00:07:18,500
{\an1}and how the galaxy was formed,
we can't just look in

129
00:07:18,533 --> 00:07:20,200
{\an1}our cosmic sort of backyard.

130
00:07:20,233 --> 00:07:23,066
{\an1}We need to look much further
afield.

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NARRATOR:
Clues to how the Milky Way

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{\an1}formed and evolved emerged

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00:07:27,333 --> 00:07:31,033
{\an1}in the 1990s, with the launch of

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00:07:31,066 --> 00:07:35,500
{\an1}the most ambitious
space telescope at the time.

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MAN:
Five, four, three, two, one.

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REPORTER:
And lift-off of the
space shuttle Discovery

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00:07:46,100 --> 00:07:48,433
{\an1}with the Hubble Space Telescope.

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♪ ♪

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00:07:52,700 --> 00:07:54,666
{\an1}Our window on the universe.

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00:07:54,700 --> 00:07:59,966
♪ ♪

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WOMAN:
Standing by for SRB separation.

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00:08:04,633 --> 00:08:08,333
{\an1}Both solid rocket boosters
have separated.

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00:08:08,366 --> 00:08:09,600
(crowd cheering)

144
00:08:09,633 --> 00:08:12,633
{\an1}(people talking in background)

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00:08:12,666 --> 00:08:17,033
♪ ♪

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00:08:28,700 --> 00:08:30,233
♪ ♪

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00:08:30,266 --> 00:08:32,833
DAS:
The Hubble Space Telescope
was one of the greatest feats

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00:08:32,866 --> 00:08:34,800
{\an1}in space missions
of human history.

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00:08:36,566 --> 00:08:39,633
TREMBLAY:
This 2.4-meter piece of glass,

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00:08:39,666 --> 00:08:41,633
{\an7}we've turned it on our universe

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00:08:41,666 --> 00:08:44,833
{\an1}and it has enabled
untold advances.

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♪ ♪

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00:08:54,100 --> 00:08:55,266
IMARA:
Images from Hubble

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00:08:55,300 --> 00:08:58,700
{\an1}transformed astronomy--
transformed science.

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00:08:58,733 --> 00:09:00,400
♪ ♪

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00:09:00,433 --> 00:09:05,433
NARRATOR:
Hubble isn't just focused on
the Milky Way.

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00:09:05,466 --> 00:09:11,066
{\an1}It also looks beyond,
much deeper into space.

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00:09:11,100 --> 00:09:13,866
{\an7}The data from Hubble
is unsurpassed.

159
00:09:13,900 --> 00:09:18,733
{\an1}It gives us the sharpest views
of galaxies

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00:09:18,766 --> 00:09:22,600
{\an1}and the distant universe.

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00:09:22,633 --> 00:09:25,300
DAS:
Hubble's a little bit like
a time machine.

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00:09:25,333 --> 00:09:27,066
{\an1}It's able to pick up light
from galaxies

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00:09:27,100 --> 00:09:28,700
that come from
very far away.

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00:09:28,733 --> 00:09:30,933
{\an1}And because they've come from
very far away,

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00:09:30,966 --> 00:09:32,533
{\an1}we're looking at them
a completely different time,

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00:09:32,566 --> 00:09:34,533
{\an7}far back in time.

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00:09:34,566 --> 00:09:37,000
{\an8}♪ ♪

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00:09:37,033 --> 00:09:41,300
{\an8}NARRATOR:
To look far back in time,
Hubble trains its gaze

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00:09:41,333 --> 00:09:45,100
{\an1}on one tiny blank patch of sky

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00:09:45,133 --> 00:09:48,366
{\an1}for over 11 days.

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00:09:48,400 --> 00:09:51,633
{\an1}What appeared was pretty
incredible.

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00:09:51,666 --> 00:09:55,166
EZZEDDINE:
We were able to see galaxies
in this ultra-deep field

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00:09:55,200 --> 00:09:58,033
{\an1}that is farther away
than we've ever, ever looked.

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♪ ♪

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00:10:05,166 --> 00:10:07,033
DAS:
So it's really given us an idea

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00:10:07,066 --> 00:10:08,433
{\an1}of how many galaxies
there are out there

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00:10:08,466 --> 00:10:10,466
{\an1}and the variety of galaxies
out there.

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00:10:10,500 --> 00:10:14,366
♪ ♪

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00:10:14,400 --> 00:10:16,866
TREMBLAY:
It's a very hard number
to estimate,

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00:10:16,900 --> 00:10:19,566
{\an1}but it is absolutely
in the trillions.

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00:10:21,766 --> 00:10:24,933
Their morphology
can be incredibly complex:

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{\an1}big train wreck mergers

183
00:10:26,466 --> 00:10:29,666
{\an1}or absolutely, stunningly,
beautifully round

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00:10:29,700 --> 00:10:31,733
{\an1}grand design spirals

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00:10:31,766 --> 00:10:32,733
{\an1}and everything in between.

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00:10:32,766 --> 00:10:36,200
♪ ♪

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00:10:36,233 --> 00:10:38,066
{\an1}There are starburst galaxies

188
00:10:38,100 --> 00:10:43,033
{\an1}that are generating new stars
at prodigious rates

189
00:10:43,066 --> 00:10:44,866
{\an1}and there are small galaxies,

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00:10:44,900 --> 00:10:46,100
{\an7}which are my favorite.

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00:10:46,133 --> 00:10:48,033
{\an7}We call them dwarf galaxies.

192
00:10:48,066 --> 00:10:51,433
{\an1}And they may be thousands
of times less massive

193
00:10:51,466 --> 00:10:53,566
{\an1}than the Milky Way,

194
00:10:53,600 --> 00:10:56,466
{\an1}but they're actually the most
common galaxy in the universe.

195
00:10:56,500 --> 00:11:00,000
♪ ♪

196
00:11:00,033 --> 00:11:03,100
NARRATOR:
Hubble tells us there are
trillions of galaxies

197
00:11:03,133 --> 00:11:05,566
in the universe.

198
00:11:05,600 --> 00:11:09,566
{\an1}And by focusing on the ones
that are the farthest away,

199
00:11:09,600 --> 00:11:14,366
{\an1}it looks deep back in time,

200
00:11:14,400 --> 00:11:17,533
{\an1}giving us a picture
of what galaxies look like

201
00:11:17,566 --> 00:11:20,200
{\an1}in their infancy.

202
00:11:20,233 --> 00:11:22,866
♪ ♪

203
00:11:30,533 --> 00:11:35,800
{\an7}And they started forming in an
era of immense cosmic activity.

204
00:11:37,833 --> 00:11:41,100
{\an7}Not long after the universe
began.

205
00:11:46,233 --> 00:11:48,766
{\an7}Before the Milky Way forms,

206
00:11:48,800 --> 00:11:53,033
{\an8}space is filled
with a vast structure

207
00:11:53,066 --> 00:11:56,633
{\an7}known as the cosmic web.

208
00:11:59,033 --> 00:12:06,466
{\an1}Hydrogen and helium gas collect
along the web's filaments.

209
00:12:06,500 --> 00:12:13,366
{\an1}But the web itself is made from
something more mysterious.

210
00:12:13,400 --> 00:12:18,033
{\an1}It's called dark matter.

211
00:12:18,066 --> 00:12:20,400
ROSARIO:
Dark matter is something
that has gravity

212
00:12:20,433 --> 00:12:22,233
{\an1}but produces no light.

213
00:12:22,266 --> 00:12:23,766
It surrounds us.

214
00:12:23,800 --> 00:12:27,000
{\an1}In fact, it dominates the mass
in our own galaxy.

215
00:12:27,033 --> 00:12:28,800
{\an1}And yet we don't know
what it is.

216
00:12:28,833 --> 00:12:32,133
{\an1}We, we can't touch it,
we can't feel it.

217
00:12:32,166 --> 00:12:34,866
COLLINS:
Galaxies really need dark matter
because it's kind of like

218
00:12:34,900 --> 00:12:37,066
{\an1}the glue that binds them all
together.

219
00:12:37,100 --> 00:12:39,800
{\an7}You can almost say it's like
the seed of galaxy formation.

220
00:12:39,833 --> 00:12:43,300
{\an7}It creates these huge structures
into which ordinary matter falls

221
00:12:43,333 --> 00:12:45,600
{\an1}and then that matter
all gets compressed

222
00:12:45,633 --> 00:12:47,100
{\an1}and can turn into stars.

223
00:12:47,133 --> 00:12:49,666
{\an1}And that really is, then,
what seeds galaxy formation

224
00:12:49,700 --> 00:12:51,833
as a whole.

225
00:12:55,800 --> 00:12:59,100
NARRATOR:
The first stars are born
where the filaments cross

226
00:12:59,133 --> 00:13:04,133
{\an1}and dark matter is at
its densest,

227
00:13:04,166 --> 00:13:07,233
{\an1}drawing large amounts
of gas together

228
00:13:07,266 --> 00:13:10,966
{\an1}until it collapses under
its own gravity.

229
00:13:13,200 --> 00:13:15,866
{\an1}Causing stars to ignite.

230
00:13:22,233 --> 00:13:27,933
♪ ♪

231
00:13:38,166 --> 00:13:44,366
{\an1}New stars in their billions
are bound together by gravity,

232
00:13:44,400 --> 00:13:47,533
{\an1}orbiting a common center.

233
00:13:50,066 --> 00:13:53,933
{\an7}These are the first galaxies.

234
00:13:53,966 --> 00:13:59,233
{\an7}Among them, the Milky Way,
in its embryonic form.

235
00:13:59,266 --> 00:14:04,166
{\an8}♪ ♪

236
00:14:04,200 --> 00:14:08,100
{\an7}A whirling disk of gas and stars

237
00:14:08,133 --> 00:14:12,400
{\an7}surrounded by an invisible halo
of dark matter.

238
00:14:17,366 --> 00:14:22,466
{\an8}♪ ♪

239
00:14:25,933 --> 00:14:27,533
{\an1}Across the universe,

240
00:14:27,566 --> 00:14:31,733
{\an1}hundreds of billions of galaxies
are forming.

241
00:14:33,866 --> 00:14:37,733
{\an1}Some-- a few dozen--
are born very close

242
00:14:37,766 --> 00:14:40,966
{\an1}to our own Milky Way.

243
00:14:41,000 --> 00:14:47,333
♪ ♪

244
00:14:47,366 --> 00:14:53,533
{\an7}Over time, gravity draws
these galaxies ever closer

245
00:14:53,566 --> 00:14:58,500
{\an7}to form what we know as
the local group.

246
00:15:01,166 --> 00:15:06,633
EZZEDDINE:
Our local group is a set of
galaxies that lies in a volume

247
00:15:06,666 --> 00:15:09,366
{\an1}of the universe that we believe

248
00:15:09,400 --> 00:15:12,433
{\an1}is gravitationally bound
together.

249
00:15:12,466 --> 00:15:16,666
{\an7}Meaning that these galaxies are
close enough that at some point

250
00:15:16,700 --> 00:15:19,766
{\an7}they might all combine together
or collide together

251
00:15:19,800 --> 00:15:24,233
{\an1}to form one big, large galaxy.

252
00:15:24,266 --> 00:15:26,533
{\an1}The galaxies within
the local group can all feel

253
00:15:26,566 --> 00:15:27,933
{\an1}one another's gravity,

254
00:15:27,966 --> 00:15:31,366
{\an1}so they're all sort of slowly
moving together with time.

255
00:15:33,033 --> 00:15:37,466
{\an8}♪ ♪

256
00:15:40,333 --> 00:15:44,000
{\an8}♪ ♪

257
00:15:44,033 --> 00:15:48,800
NARRATOR:
Just three billion years
after the Milky Way began,

258
00:15:48,833 --> 00:15:54,866
{\an1}it rises in the night sky
of its first planets,

259
00:15:54,900 --> 00:16:00,000
{\an1}but with only half the stars
and a more irregular structure

260
00:16:00,033 --> 00:16:04,766
{\an1}than the mature galaxy
we see today.

261
00:16:04,800 --> 00:16:10,366
{\an1}So how did our galaxy
get its spirals?

262
00:16:11,566 --> 00:16:17,766
{\an1}To answer the question,
a new spacecraft is built.

263
00:16:17,800 --> 00:16:21,833
{\an1}Gaia will look directly
at the Milky Way itself.

264
00:16:23,733 --> 00:16:30,366
{\an1}Its designers are determined
to overcome an age-old problem:

265
00:16:30,400 --> 00:16:33,900
{\an1}how to measure the true distance
between stars.

266
00:16:33,933 --> 00:16:37,433
TREMBLAY:
Being able to determine
the distance to objects

267
00:16:37,466 --> 00:16:40,200
{\an1}is one of the most
fundamental things

268
00:16:40,233 --> 00:16:43,666
{\an1}you need to do to understand
the structure of our universe.

269
00:16:43,700 --> 00:16:47,600
NARRATOR:
To measure the distances
accurately,

270
00:16:47,633 --> 00:16:50,766
{\an1}Gaia's engineers must devise
an orbit for the craft

271
00:16:50,800 --> 00:16:55,433
{\an1}big enough that it can measure
the same star from two points

272
00:16:55,466 --> 00:17:00,600
very far apart,
called a parallax measurement.

273
00:17:00,633 --> 00:17:03,133
{\an1}Gaia will need to travel

274
00:17:03,166 --> 00:17:05,966
{\an1}almost a million miles
from Earth.

275
00:17:06,000 --> 00:17:09,633
WOMAN:
Attention pour la décompte
finale.

276
00:17:09,666 --> 00:17:12,200
Dix, neuf, huit,

277
00:17:12,233 --> 00:17:14,566
sept, six,

278
00:17:14,600 --> 00:17:17,766
{\an1}cinq, quatre, trois,

279
00:17:17,800 --> 00:17:20,800
{\an1}deux, un, top-- décollage.

280
00:17:30,566 --> 00:17:33,033
{\an1}I've been involved in Gaia since
the very beginning of it.

281
00:17:38,333 --> 00:17:41,466
{\an7}It was a beautiful launch,
really spectacular.

282
00:17:41,500 --> 00:17:44,100
{\an7}(woman speaking French)

283
00:17:44,133 --> 00:17:46,666
{\an8}NARRATOR:
The spacecraft shares the name

284
00:17:46,700 --> 00:17:50,800
{\an7}of the ancient Greek
Earth goddess, Gaia.

285
00:17:50,833 --> 00:17:53,800
GILMORE:
It took four minutes.

286
00:17:53,833 --> 00:17:56,200
{\an1}You could see the flame
of the rocket

287
00:17:56,233 --> 00:18:00,566
{\an1}and you could see the individual
stages popping off.

288
00:18:00,600 --> 00:18:02,966
♪ ♪

289
00:18:03,000 --> 00:18:05,000
{\an1}Then they got into this critical
state where they had to

290
00:18:05,033 --> 00:18:06,133
{\an1}open up the sun shields.

291
00:18:06,166 --> 00:18:08,100
It was critical
that this opened up

292
00:18:08,133 --> 00:18:11,600
{\an1}and protect the payload
from the sun.

293
00:18:11,633 --> 00:18:13,900
{\an7}And that was the do-or-die
moment.

294
00:18:13,933 --> 00:18:19,033
♪ ♪

295
00:18:24,833 --> 00:18:28,500
NARRATOR:
Gaia's mission is to map
the true positions

296
00:18:28,533 --> 00:18:32,566
{\an1}of a billion stars
in our Milky Way--

297
00:18:32,600 --> 00:18:38,000
{\an1}nearly all of them
for the first time.

298
00:18:38,033 --> 00:18:41,600
BELOKUROV:
Before Gaia, we just looked at

299
00:18:41,633 --> 00:18:43,433
{\an7}the images of our galaxy.

300
00:18:43,466 --> 00:18:46,300
{\an7}We were missing half of
the information.

301
00:18:47,866 --> 00:18:49,433
GILMORE:
Gaia is the first-ever

302
00:18:49,466 --> 00:18:51,166
{\an1}precision distance
measuring machine

303
00:18:51,200 --> 00:18:53,400
{\an1}that mankind has ever had.

304
00:18:53,433 --> 00:18:57,300
{\an8}♪ ♪

305
00:18:57,333 --> 00:19:00,600
{\an8}NARRATOR:
So how is it possible for Gaia
to map the Milky Way

306
00:19:00,633 --> 00:19:03,400
{\an7}so accurately from within?

307
00:19:03,433 --> 00:19:06,633
{\an8}♪ ♪

308
00:19:06,666 --> 00:19:10,200
{\an7}First, it travels to its
distant vantage point

309
00:19:10,233 --> 00:19:15,633
{\an8}called L2,
a gravitational sweet spot.

310
00:19:15,666 --> 00:19:18,466
{\an8}It can hold here
with minimal fuel use

311
00:19:18,500 --> 00:19:25,100
{\an7}as it follows the Earth in its
extensive orbit around the sun.

312
00:19:25,133 --> 00:19:27,333
{\an8}ROSARIO:
Astronomy has always been
at the forefront of technology,

313
00:19:27,366 --> 00:19:29,366
{\an7}but the kind of technology
we work with right now

314
00:19:29,400 --> 00:19:30,966
{\an7}is absolutely amazing.

315
00:19:31,000 --> 00:19:34,333
♪ ♪

316
00:19:34,366 --> 00:19:38,866
NARRATOR:
With just a whisper of nitrogen
to help Gaia's telescopes

317
00:19:38,900 --> 00:19:42,600
sweep smoothly
through 360 degrees

318
00:19:42,633 --> 00:19:45,166
{\an1}four times a day,

319
00:19:45,200 --> 00:19:49,266
{\an1}it makes over one-and-a-half
million observations an hour.

320
00:19:49,300 --> 00:19:53,800
♪ ♪

321
00:19:53,833 --> 00:19:55,233
{\an1}After four months,

322
00:19:55,266 --> 00:19:58,733
{\an1}it has looked at the whole sky
at least once.

323
00:19:58,766 --> 00:20:02,533
♪ ♪

324
00:20:02,566 --> 00:20:05,633
{\an1}Gaia gathers data
on the brightest stars

325
00:20:05,666 --> 00:20:10,233
{\an1}across the whole sky--

326
00:20:10,266 --> 00:20:13,533
{\an1}stars within the disk
of the galaxy,

327
00:20:13,566 --> 00:20:17,033
{\an1}from the center to the halo
and beyond.

328
00:20:17,066 --> 00:20:20,333
♪ ♪

329
00:20:20,366 --> 00:20:24,366
{\an1}After it has traveled millions
of miles in its orbit,

330
00:20:24,400 --> 00:20:28,566
{\an1}it observes the same stars
from a different vantage point.

331
00:20:28,600 --> 00:20:33,200
♪ ♪

332
00:20:33,233 --> 00:20:38,766
{\an1}After nearly two years
of almost non-stop sky-scanning,

333
00:20:38,800 --> 00:20:42,266
{\an1}scientists can triangulate
the true position

334
00:20:42,300 --> 00:20:45,533
{\an1}of over a billion stars

335
00:20:45,566 --> 00:20:49,800
{\an1}for the most accurate map
of the galaxy ever created.

336
00:20:49,833 --> 00:20:53,433
♪ ♪

337
00:20:53,466 --> 00:20:56,600
The Gaia map.

338
00:20:59,000 --> 00:21:01,200
BELOKUROV:
The Gaia data has allowed us

339
00:21:01,233 --> 00:21:05,266
{\an1}to see our own galaxy
like never before.

340
00:21:05,300 --> 00:21:07,233
EZZEDDINE:
I think that Gaia opened up

341
00:21:07,266 --> 00:21:11,000
{\an1}a really new axis of information
to us

342
00:21:11,033 --> 00:21:13,800
{\an1}that we just have never imagined
it would do.

343
00:21:13,833 --> 00:21:16,700
{\an7}These are like having
completely, you know,

344
00:21:16,733 --> 00:21:18,233
{\an7}revolutionary cartographers

345
00:21:18,266 --> 00:21:23,566
{\an1}make an entirely new map
of our home galaxy.

346
00:21:27,666 --> 00:21:33,600
NARRATOR:
Finally, astronomers have
their Holy Grail:

347
00:21:33,633 --> 00:21:38,733
the Milky Way,
mapped in three dimensions.

348
00:21:40,300 --> 00:21:44,966
GILMORE:
This is our first-ever honest
3D picture of the Milky Way.

349
00:21:45,000 --> 00:21:47,900
{\an1}It's not a simulation
from a computer

350
00:21:47,933 --> 00:21:51,966
{\an1}and it is not an, an attempt at
guessing the structure

351
00:21:52,000 --> 00:21:53,900
{\an1}from approximate data.

352
00:21:53,933 --> 00:21:55,533
{\an1}Every one of those stars
is individually measured

353
00:21:55,566 --> 00:21:56,766
{\an1}to high precisions.

354
00:21:56,800 --> 00:22:00,166
{\an1}So this means that we can
move ourselves around

355
00:22:00,200 --> 00:22:02,433
{\an1}through this and see, well, what
does this bit of the Milky Way

356
00:22:02,466 --> 00:22:04,133
{\an1}actually look like?

357
00:22:04,166 --> 00:22:06,133
{\an1}And you decide you want to look
at it from far away,

358
00:22:06,166 --> 00:22:07,433
{\an1}and you can do that.

359
00:22:07,466 --> 00:22:09,100
{\an1}Or you can zoom in close
and say, "I want to know

360
00:22:09,133 --> 00:22:10,433
{\an1}"how that star cluster works.

361
00:22:10,466 --> 00:22:11,966
{\an1}I'll go and sit inside it."

362
00:22:12,000 --> 00:22:13,400
{\an1}Gaia can tell the difference
between a star

363
00:22:13,433 --> 00:22:14,933
{\an1}that's at the front of
that cluster

364
00:22:14,966 --> 00:22:17,300
{\an1}and a star that's at the back
of that cluster,

365
00:22:17,333 --> 00:22:20,800
{\an1}even though the cluster itself
is 5,000 light years away.

366
00:22:20,833 --> 00:22:22,733
{\an1}Gaia is not only measuring where
things are

367
00:22:22,766 --> 00:22:25,433
{\an1}to delightful precision,

368
00:22:25,466 --> 00:22:26,933
but equally,
you can see things moving.

369
00:22:26,966 --> 00:22:32,566
{\an1}And it's actually the moving
that's the critical bit.

370
00:22:32,600 --> 00:22:37,433
NARRATOR:
In addition to mapping stars
in three-dimensional space,

371
00:22:37,466 --> 00:22:40,566
{\an1}Gaia captured another dimension,

372
00:22:40,600 --> 00:22:45,133
{\an1}the result of its repeated trips
around the sun:

373
00:22:45,166 --> 00:22:48,533
time.

374
00:22:48,566 --> 00:22:50,400
{\an1}This data could help us
understand

375
00:22:50,433 --> 00:22:54,633
{\an1}how our galaxy evolved.

376
00:22:54,666 --> 00:22:58,466
ROSARIO:
Gaia doesn't just tell us where
the stars are in the sky,

377
00:22:58,500 --> 00:23:03,466
{\an1}but also how fast they're moving
across the sky and towards us,

378
00:23:03,500 --> 00:23:05,500
{\an1}and that's an essential bit

379
00:23:05,533 --> 00:23:09,333
{\an1}of information to understand how
things change over time.

380
00:23:09,366 --> 00:23:14,200
NARRATOR:
Once scientists know
how a star is moving,

381
00:23:14,233 --> 00:23:16,600
{\an1}they can use Newtonian mechanics

382
00:23:16,633 --> 00:23:20,466
{\an1}to calculate where it is going.

383
00:23:20,500 --> 00:23:24,666
{\an1}And using the same calculations,
they can reverse the motion

384
00:23:24,700 --> 00:23:29,466
{\an1}of the star to uncover
where it has been.

385
00:23:29,500 --> 00:23:34,033
{\an1}This new data is revolutionizing
a field of science

386
00:23:34,066 --> 00:23:37,600
{\an1}known as galactic archaeology.

387
00:23:37,633 --> 00:23:41,066
ROSARIO:
Galactic archaeology
is the process of identifying

388
00:23:41,100 --> 00:23:44,033
{\an1}the history and the motion
of stars

389
00:23:44,066 --> 00:23:47,533
{\an1}so you can figure out
where stars come from,

390
00:23:47,566 --> 00:23:53,033
{\an1}how old they are, and how their
motions change over time.

391
00:23:53,066 --> 00:23:54,700
♪ ♪

392
00:23:54,733 --> 00:23:57,533
DAS:
What's been really incredible
about Gaia is, if we couple it

393
00:23:57,566 --> 00:24:01,133
{\an1}with spectra that we're
observing back on Earth,

394
00:24:01,166 --> 00:24:03,200
{\an7}we're able to date the stars
and really use them

395
00:24:03,233 --> 00:24:04,933
{\an7}as the fossils that they're
supposed to be.

396
00:24:04,966 --> 00:24:08,333
{\an7}So this means we can work out
what the fossils tell us about

397
00:24:08,366 --> 00:24:10,800
{\an1}the evolutionary events that
happened in the Milky Way's past

398
00:24:10,833 --> 00:24:12,033
{\an1}and then date them.

399
00:24:12,066 --> 00:24:14,933
So put them in
chronological order.

400
00:24:14,966 --> 00:24:17,033
{\an7}So we combine everything
together in order to get

401
00:24:17,066 --> 00:24:21,300
{\an7}a really clear understanding
of how the Milky Way came to be.

402
00:24:21,333 --> 00:24:25,866
♪ ♪

403
00:24:25,900 --> 00:24:30,133
NARRATOR:
This new data from Gaia has
helped scientists spot a pattern

404
00:24:30,166 --> 00:24:32,000
{\an1}between the Milky Way

405
00:24:32,033 --> 00:24:38,033
{\an1}and our neighborhood cluster
of galaxies, the local group.

406
00:24:38,066 --> 00:24:40,766
DAS:
The important thing to know
about our galactic neighbors

407
00:24:40,800 --> 00:24:42,400
{\an1}in the local group
is that nothing's actually

408
00:24:42,433 --> 00:24:43,700
sitting still.

409
00:24:43,733 --> 00:24:46,266
{\an1}Gravity means that we're all
moving towards or away

410
00:24:46,300 --> 00:24:47,233
{\an1}from each other and we're

411
00:24:47,266 --> 00:24:50,133
{\an1}sort of playing a dance
out there.

412
00:24:50,166 --> 00:24:53,200
♪ ♪

413
00:24:53,233 --> 00:24:54,733
IMARA:
Gravity is

414
00:24:54,766 --> 00:24:56,666
{\an7}the great cosmic attractor.

415
00:24:56,700 --> 00:25:00,133
{\an1}This dance of the galaxy
and its neighbors

416
00:25:00,166 --> 00:25:03,200
{\an1}have been going on
for billions of years.

417
00:25:03,233 --> 00:25:05,166
♪ ♪

418
00:25:05,200 --> 00:25:07,966
NARRATOR:
Gaia is only just now revealing
the steps

419
00:25:08,000 --> 00:25:12,000
{\an1}to this intricate
intergalactic dance.

420
00:25:12,033 --> 00:25:16,133
♪ ♪

421
00:25:16,166 --> 00:25:19,566
BOSE:
When the Gaia satellite started
producing its data,

422
00:25:19,600 --> 00:25:22,300
{\an7}and astronomers started
analyzing this data,

423
00:25:22,333 --> 00:25:24,266
{\an7}there was something rather
curious.

424
00:25:24,300 --> 00:25:26,833
{\an7}A large sample of stars
were found that seemed to be

425
00:25:26,866 --> 00:25:29,266
{\an7}rotating in the opposite
direction to the majority

426
00:25:29,300 --> 00:25:31,400
{\an7}of stars in the Milky Way disk.

427
00:25:31,433 --> 00:25:33,466
{\an1}And that's really unusual.

428
00:25:33,500 --> 00:25:35,700
{\an1}And it was really surprising.

429
00:25:35,733 --> 00:25:37,966
TREMBLAY:
So that means that not all
of the stars

430
00:25:38,000 --> 00:25:39,833
{\an1}that make up our galaxy,
the Milky Way,

431
00:25:39,866 --> 00:25:41,466
{\an1}were actually born here.

432
00:25:41,500 --> 00:25:44,400
COLLINS:
They probably came from
a different galaxy altogether.

433
00:25:44,433 --> 00:25:46,766
{\an1}So they're almost these alien
stars that have been brought in.

434
00:25:46,800 --> 00:25:50,833
NARRATOR:
Gaia's data led scientists

435
00:25:50,866 --> 00:25:55,333
{\an1}to make an astonishing
discovery.

436
00:25:55,366 --> 00:25:57,433
ROSARIO:
So the most mind-blowing thing

437
00:25:57,466 --> 00:26:00,966
{\an1}is that those stars
are the remnants

438
00:26:01,000 --> 00:26:03,133
{\an1}of a humongous collision,

439
00:26:03,166 --> 00:26:05,866
{\an1}and they actually come from
another galaxy.

440
00:26:05,900 --> 00:26:10,800
{\an8}♪ ♪

441
00:26:17,066 --> 00:26:23,866
{\an8}NARRATOR:
If we could travel back in time
ten billion years

442
00:26:23,900 --> 00:26:30,133
{\an7}and land on one of the earliest
planets within our Milky Way,

443
00:26:30,166 --> 00:26:34,766
{\an7}we'd see something spectacular
in the night sky.

444
00:26:34,800 --> 00:26:41,433
{\an8}♪ ♪

445
00:26:41,466 --> 00:26:47,733
{\an7}Billions of stars coming into
view heading towards us.

446
00:26:47,766 --> 00:26:52,233
{\an8}♪ ♪

447
00:26:52,266 --> 00:26:55,000
{\an7}The Milky Way is about
to collide

448
00:26:55,033 --> 00:26:58,233
{\an7}with another galaxy from
our local group.

449
00:26:58,266 --> 00:27:01,466
{\an8}♪ ♪

450
00:27:01,500 --> 00:27:05,000
{\an7}Called Gaia-Enceladus.

451
00:27:07,500 --> 00:27:12,200
♪ ♪

452
00:27:15,700 --> 00:27:22,000
♪ ♪

453
00:27:23,633 --> 00:27:27,633
{\an1}A quarter of the size
of our galaxy,

454
00:27:27,666 --> 00:27:33,333
{\an1}Gaia-Enceladus is drawn
into the Milky Way,

455
00:27:33,366 --> 00:27:36,466
{\an1}bringing disorder to its
flat disk.

456
00:27:39,433 --> 00:27:40,733
When you look at
a galaxy merger,

457
00:27:40,766 --> 00:27:42,766
{\an1}it looks like an incredibly
violent process,

458
00:27:42,800 --> 00:27:44,966
{\an1}but it's actually something
that's incredibly elegant,

459
00:27:45,000 --> 00:27:48,066
{\an1}and that is because galaxies
are, ultimately,

460
00:27:48,100 --> 00:27:49,700
{\an1}mostly empty space.

461
00:27:49,733 --> 00:27:52,766
{\an1}And so when galaxies collide
or crash together,

462
00:27:52,800 --> 00:27:55,233
{\an1}they pass through one another
like ghosts.

463
00:27:55,266 --> 00:27:59,300
{\an1}The chance for a star-star
collision in a galaxy merger

464
00:27:59,333 --> 00:28:02,700
{\an1}is actually exquisitely low.

465
00:28:02,733 --> 00:28:05,333
BOSE:
It's really quite
a beautiful process,

466
00:28:05,366 --> 00:28:08,333
{\an1}because the way in which
the mutual gravity

467
00:28:08,366 --> 00:28:11,066
{\an1}of these two galaxies actually
interact with one another

468
00:28:11,100 --> 00:28:14,133
{\an1}causes one to start
sort of spiraling around.

469
00:28:14,166 --> 00:28:16,600
{\an1}Once it, you know, plunges in,
it spirals around it,

470
00:28:16,633 --> 00:28:19,900
{\an1}and then comes back and returns,
so it's kind of like, you know,

471
00:28:19,933 --> 00:28:22,333
{\an1}two objects in a sort of
celestial ballet

472
00:28:22,366 --> 00:28:23,900
{\an1}around one another.

473
00:28:23,933 --> 00:28:26,200
ROSARIO:
A collision can change the
structure of a galaxy,

474
00:28:26,233 --> 00:28:29,466
{\an1}reorders the stars in the
galaxy, gives them new orbits,

475
00:28:29,500 --> 00:28:31,300
moves the gas
into different places.

476
00:28:31,333 --> 00:28:33,733
{\an1}And so you end up with something
that looks different,

477
00:28:33,766 --> 00:28:34,733
{\an1}that behaves differently.

478
00:28:34,766 --> 00:28:38,566
♪ ♪

479
00:28:38,600 --> 00:28:42,533
NARRATOR:
The invisible driver
of all these interactions

480
00:28:42,566 --> 00:28:48,100
{\an1}is the same stuff that formed
the galaxies in the first place:

481
00:28:48,133 --> 00:28:50,800
dark matter.

482
00:28:50,833 --> 00:28:52,400
♪ ♪

483
00:28:52,433 --> 00:28:55,400
ROSARIO:
Because it accounts for most of
the gravity in the galaxy,

484
00:28:55,433 --> 00:28:57,166
{\an1}it is dark matter that
determines

485
00:28:57,200 --> 00:28:59,933
{\an1}how violent the collision is,
how rapidly

486
00:28:59,966 --> 00:29:03,866
{\an1}and with what intensity galaxies
come together when they collide.

487
00:29:03,900 --> 00:29:05,366
{\an8}In many ways,

488
00:29:05,400 --> 00:29:09,200
{\an7}it determines how galaxies
end up after a collision.

489
00:29:09,233 --> 00:29:12,533
♪ ♪

490
00:29:17,766 --> 00:29:22,200
NARRATOR:
Just a few billion years after
the Milky Way formed,

491
00:29:22,233 --> 00:29:25,700
{\an1}already much more massive than
Gaia-Enceladus...

492
00:29:28,466 --> 00:29:32,733
{\an1}...the Milky Way's gravity
overwhelms its neighbor.

493
00:29:35,300 --> 00:29:37,933
{\an1}Absorbing it entirely.

494
00:29:37,966 --> 00:29:41,933
♪ ♪

495
00:29:49,033 --> 00:29:53,533
{\an1}The Milky Way is bigger by
a billion stars.

496
00:29:53,566 --> 00:29:59,933
♪ ♪

497
00:29:59,966 --> 00:30:01,433
ROSARIO:
For the first time ever,

498
00:30:01,466 --> 00:30:04,366
{\an1}we have seen how our Milky Way
has grown bigger.

499
00:30:07,100 --> 00:30:09,233
COLLINS:
What we've learnt
from this collision

500
00:30:09,266 --> 00:30:12,533
{\an1}is really about how much richer
our galaxy grew,

501
00:30:12,566 --> 00:30:15,733
{\an1}but it doesn't actually tell us
about us yet.

502
00:30:17,633 --> 00:30:21,100
NARRATOR:
To find out how
our solar system got here,

503
00:30:21,133 --> 00:30:23,533
{\an1}scientists have been
tracing the history

504
00:30:23,566 --> 00:30:27,666
{\an1}of another unusual group
of stars.

505
00:30:27,700 --> 00:30:31,166
♪ ♪

506
00:30:31,200 --> 00:30:34,666
{\an1}They loop around our
galactic disk

507
00:30:34,700 --> 00:30:40,333
{\an1}in a spectacular trail called
the Sagittarius Stream.

508
00:30:40,366 --> 00:30:42,600
COLLINS:
So the Sagittarius Stream
is really interesting

509
00:30:42,633 --> 00:30:44,533
{\an1}because it might actually help
us understand

510
00:30:44,566 --> 00:30:47,366
{\an1}where we came from.

511
00:30:47,400 --> 00:30:49,933
BOSE:
It is what's known as a
tidal stream,

512
00:30:49,966 --> 00:30:51,366
{\an1}which is a stream of stars

513
00:30:51,400 --> 00:30:53,633
{\an1}that have been stretched
across the night sky

514
00:30:53,666 --> 00:30:56,533
{\an1}due to the gravity of the
Milky Way.

515
00:30:56,566 --> 00:30:59,266
EZZEDDINE:
The Sagittarius Stream
is so big,

516
00:30:59,300 --> 00:31:02,566
{\an1}it goes all the way up and even
all the way down,

517
00:31:02,600 --> 00:31:06,100
{\an1}so we can just carry
the Milky Way from its handle.

518
00:31:06,133 --> 00:31:09,900
{\an1}It's really, really large
stream.

519
00:31:09,933 --> 00:31:12,433
NARRATOR:
The trail of stars we see today

520
00:31:12,466 --> 00:31:16,633
{\an1}is named after the galaxy that
they used to belong to,

521
00:31:16,666 --> 00:31:20,733
{\an1}Sagittarius Dwarf.

522
00:31:20,766 --> 00:31:23,433
GILMORE:
The Sagittarius galaxy

523
00:31:23,466 --> 00:31:26,733
{\an1}was discovered by a student
and myself in the '90s.

524
00:31:26,766 --> 00:31:29,400
{\an1}Most of the Sagittarius galaxy
is actually spread out

525
00:31:29,433 --> 00:31:31,433
{\an1}into two streams, one in the
front and out the back,

526
00:31:31,466 --> 00:31:34,466
{\an1}like giant comet tails wrapping
around the entire sky,

527
00:31:34,500 --> 00:31:37,200
{\an1}going out for maybe
100,000 light years away.

528
00:31:37,233 --> 00:31:39,500
♪ ♪

529
00:31:39,533 --> 00:31:41,000
{\an1}We could see these,

530
00:31:41,033 --> 00:31:43,533
{\an1}but it wasn't possible to
understand how they got there.

531
00:31:45,500 --> 00:31:48,800
Now, with Gaia,
we have motions of these stars,

532
00:31:48,833 --> 00:31:51,033
{\an1}so we can see what direction
they're moving in,

533
00:31:51,066 --> 00:31:53,700
{\an1}which ones are going fast,
which ones are going slow.

534
00:31:55,433 --> 00:31:57,200
{\an1}For the first time ever,

535
00:31:57,233 --> 00:32:00,766
{\an7}it's been possible to say,
"Ah, this is what happened!"

536
00:32:02,266 --> 00:32:05,300
BOSE:
The Sagittarius Stream is
essentially the tidal debris

537
00:32:05,333 --> 00:32:08,600
{\an1}that has been left over when
a dwarf galaxy,

538
00:32:08,633 --> 00:32:12,033
{\an1}the Sagittarius Dwarf, actually
plunged into the Milky Way.

539
00:32:16,400 --> 00:32:19,233
NARRATOR:
By studying the stream of stars,

540
00:32:19,266 --> 00:32:21,766
{\an1}scientists have uncovered
the story

541
00:32:21,800 --> 00:32:25,200
{\an1}of a much more recent
galactic collision.

542
00:32:29,100 --> 00:32:32,733
{\an8}This time,
with a much smaller galaxy.

543
00:32:35,733 --> 00:32:40,000
GILMORE:
When the Sagittarius galaxy
orbited into the Milky Way,

544
00:32:40,033 --> 00:32:42,733
{\an1}it came, foolishly,
rather far in.

545
00:32:42,766 --> 00:32:49,066
♪ ♪

546
00:32:49,100 --> 00:32:52,400
NARRATOR:
As it dives towards the
Milky Way,

547
00:32:52,433 --> 00:32:56,766
{\an1}the dwarf galaxy begins
to have its stars pulled off.

548
00:32:59,966 --> 00:33:01,366
GILMORE:
When it goes through the disk,

549
00:33:01,400 --> 00:33:04,266
{\an1}it punches a hole in the disk,
and the stars get

550
00:33:04,300 --> 00:33:07,200
{\an1}put in particular patterns.

551
00:33:07,233 --> 00:33:09,833
{\an1}And it's got stretched into
these two great long streams.

552
00:33:09,866 --> 00:33:14,566
♪ ♪

553
00:33:14,600 --> 00:33:19,433
NARRATOR:
The much smaller galaxy
encroaches upon the Milky Way,

554
00:33:19,466 --> 00:33:21,966
{\an1}just like Gaia-Enceladus did,

555
00:33:22,000 --> 00:33:24,800
{\an1}but the timing is intriguing,

556
00:33:24,833 --> 00:33:29,033
{\an1}because this collision happens
just before

557
00:33:29,066 --> 00:33:32,800
the birth of
our own solar system.

558
00:33:32,833 --> 00:33:36,433
TREMBLAY:
One of the most important
consequences of galaxy mergers,

559
00:33:36,466 --> 00:33:38,466
{\an1}like the destruction of the
Sagittarius Dwarf galaxy

560
00:33:38,500 --> 00:33:39,866
{\an1}by the Milky Way,

561
00:33:39,900 --> 00:33:44,366
{\an7}is a new, fresh injection
of gas into the galaxy, right?

562
00:33:44,400 --> 00:33:47,466
{\an8}And it is gas,
particularly cold gas,

563
00:33:47,500 --> 00:33:50,433
{\an1}that is the fuel from which
all stars are born.

564
00:33:50,466 --> 00:33:52,366
DAS:
For star formation to occur,

565
00:33:52,400 --> 00:33:54,233
basically,
the colder, the better.

566
00:33:54,266 --> 00:33:57,033
♪ ♪

567
00:34:04,800 --> 00:34:08,500
NARRATOR:
The most important gas
that the collisions bring

568
00:34:08,533 --> 00:34:10,900
{\an1}is made of one of the oldest

569
00:34:10,933 --> 00:34:14,666
{\an1}and most ubiquitous elements
in the universe.

570
00:34:16,733 --> 00:34:22,300
(birds chirping)

571
00:34:22,333 --> 00:34:25,166
{\an1}(radio static buzzing)

572
00:34:25,200 --> 00:34:30,400
{\an7}So what I'm listening to here
is the lifeblood of our galaxy,

573
00:34:30,433 --> 00:34:32,166
hydrogen.

574
00:34:32,200 --> 00:34:34,566
{\an1}We can detect it with
our radio telescopes,

575
00:34:34,600 --> 00:34:36,933
{\an1}like in this case,
pointing right at the Milky Way.

576
00:34:36,966 --> 00:34:40,266
{\an7}Hydrogen is the most common
element in the universe,

577
00:34:40,300 --> 00:34:43,666
{\an7}and it's in our own galaxy.

578
00:34:43,700 --> 00:34:45,600
{\an1}We don't see gas with our eyes,

579
00:34:45,633 --> 00:34:47,600
{\an1}and therefore we are
not used to the idea

580
00:34:47,633 --> 00:34:50,733
{\an1}of there being plenty of gas
in the Milky Way.

581
00:34:50,766 --> 00:34:53,300
{\an1}But if you use a radio
telescope, you can see it.

582
00:34:53,333 --> 00:34:55,633
{\an1}You can look at the radiation
coming from that gas,

583
00:34:55,666 --> 00:34:57,500
{\an1}and that's exactly what
we're doing right now.

584
00:34:57,533 --> 00:35:01,266
{\an1}This gas is connected
to stars deeply--

585
00:35:01,300 --> 00:35:02,933
{\an1}it's what stars form from.

586
00:35:02,966 --> 00:35:07,400
{\an1}If this gas wasn't there,
stars would never have formed.

587
00:35:25,366 --> 00:35:30,100
NARRATOR:
Hydrogen was created shortly
after the birth of the universe,

588
00:35:30,133 --> 00:35:33,433
{\an1}and it has always been spread
throughout the Milky Way.

589
00:35:35,200 --> 00:35:38,300
But not evenly.

590
00:35:38,333 --> 00:35:41,566
{\an1}It clumps together in
dense clouds

591
00:35:41,600 --> 00:35:43,800
{\an1}that, in this iconic image,

592
00:35:43,833 --> 00:35:47,100
{\an1}extend up to 30 trillion miles.

593
00:35:48,633 --> 00:35:52,033
{\an1}Scientists call them
stellar nurseries,

594
00:35:52,066 --> 00:35:57,066
{\an1}where temperatures are
low enough for gas to condense.

595
00:35:57,100 --> 00:35:59,133
IMARA:
Stellar nurseries

596
00:35:59,166 --> 00:36:01,666
are some
of the largest, coldest,

597
00:36:01,700 --> 00:36:05,966
{\an1}and certainly among the darkest
regions within any galaxy.

598
00:36:06,000 --> 00:36:09,066
♪ ♪

599
00:36:09,100 --> 00:36:12,433
{\an1}If you were to fly through
a stellar nursery,

600
00:36:12,466 --> 00:36:17,100
{\an1}it would be extremely cold,
and it's an extremely

601
00:36:17,133 --> 00:36:22,100
{\an7}turbulent and chaotic place,
pervaded by magnetic fields,

602
00:36:22,133 --> 00:36:25,266
{\an7}and, and charged particles
streaming throughout.

603
00:36:25,300 --> 00:36:27,600
♪ ♪

604
00:36:27,633 --> 00:36:30,100
{\an1}It might be glowing
a little bit,

605
00:36:30,133 --> 00:36:32,433
{\an1}and as you approach
closer and closer,

606
00:36:32,466 --> 00:36:35,100
{\an1}you would realize that
it's actually heating up a bit.

607
00:36:35,133 --> 00:36:37,700
{\an1}It's, it's actually becoming
warmer.

608
00:36:37,733 --> 00:36:40,966
{\an1}You would perhaps surmise that
this is where

609
00:36:41,000 --> 00:36:43,266
{\an1}a new group of stars is
being born.

610
00:36:43,300 --> 00:36:50,133
♪ ♪

611
00:36:50,166 --> 00:36:51,600
COLLINS:
Hydrogen can be thought of

612
00:36:51,633 --> 00:36:53,300
{\an7}as the lifeblood of galaxies,

613
00:36:53,333 --> 00:36:55,100
{\an7}because it's the first building
block of stars.

614
00:36:55,133 --> 00:36:58,766
{\an7}In the center of a star,
it's fusing hydrogen together

615
00:36:58,800 --> 00:37:00,300
{\an1}all the time to produce helium.

616
00:37:00,333 --> 00:37:02,566
{\an1}And that gives off energy,
which allows the stars

617
00:37:02,600 --> 00:37:04,533
to light up.

618
00:37:04,566 --> 00:37:07,833
♪ ♪

619
00:37:15,100 --> 00:37:17,933
NARRATOR:
When the Sagittarius Dwarf
galaxy

620
00:37:17,966 --> 00:37:19,733
{\an1}collides with our Milky Way,

621
00:37:19,766 --> 00:37:24,000
{\an1}it brings more hydrogen
to these clouds,

622
00:37:24,033 --> 00:37:27,766
{\an1}triggering a new era
of star birth.

623
00:37:27,800 --> 00:37:30,200
♪ ♪

624
00:37:30,233 --> 00:37:33,400
BOSE:
When galaxies interact with
one another

625
00:37:33,433 --> 00:37:35,133
{\an1}and they collide with one
another,

626
00:37:35,166 --> 00:37:39,100
{\an7}what typically happens is that
you actually get

627
00:37:39,133 --> 00:37:42,733
{\an7}a big burst of star formation
occurring.

628
00:37:42,766 --> 00:37:44,133
{\an1}And that's primarily because

629
00:37:44,166 --> 00:37:47,100
{\an1}you are essentially bringing
in a new source

630
00:37:47,133 --> 00:37:51,466
{\an1}of star-forming fuel into the
Milky Way.

631
00:37:51,500 --> 00:37:57,066
♪ ♪

632
00:37:57,100 --> 00:38:02,333
NARRATOR:
This era coincides with
the birth of our own sun,

633
00:38:02,366 --> 00:38:05,266
{\an1}4.6 billion years ago.

634
00:38:05,300 --> 00:38:08,500
♪ ♪

635
00:38:08,533 --> 00:38:11,966
DAS:
The jury's still out,
but we think that the sun

636
00:38:12,000 --> 00:38:14,800
{\an7}could have formed in that first
enhancement in star formation.

637
00:38:14,833 --> 00:38:17,600
♪ ♪

638
00:38:17,633 --> 00:38:21,266
EZZEDDINE:
The timing of the collision
between the Milky Way galaxy

639
00:38:21,300 --> 00:38:24,100
{\an1}and the Sagittarius Dwarf galaxy

640
00:38:24,133 --> 00:38:27,000
{\an7}coincides with a peak in
star formation

641
00:38:27,033 --> 00:38:28,800
{\an7}that we see happen in our
Milky Way.

642
00:38:28,833 --> 00:38:30,466
♪ ♪

643
00:38:30,500 --> 00:38:33,133
And we know that
the age of the gas

644
00:38:33,166 --> 00:38:35,600
{\an1}in which our solar system
was formed

645
00:38:35,633 --> 00:38:40,566
{\an1}lies very close to this spike
in star formation.

646
00:38:40,600 --> 00:38:42,666
♪ ♪

647
00:38:42,700 --> 00:38:44,800
TREMBLAY:
It is certainly possible, right?

648
00:38:44,833 --> 00:38:46,533
{\an1}That our own solar system

649
00:38:46,566 --> 00:38:48,966
{\an1}is anchored around a star

650
00:38:49,000 --> 00:38:52,533
{\an1}that was born from gas that
did not originate

651
00:38:52,566 --> 00:38:57,200
{\an1}in our home galaxy--
it was taken, it was pulled,

652
00:38:57,233 --> 00:39:00,033
{\an1}or consumed by the Milky Way

653
00:39:00,066 --> 00:39:02,433
{\an1}when it ripped apart
a satellite galaxy,

654
00:39:02,466 --> 00:39:05,333
maybe even
the Sagittarius Dwarf.

655
00:39:08,266 --> 00:39:14,200
NARRATOR:
For a small galaxy, Sagittarius
Dwarf has had a big impact,

656
00:39:14,233 --> 00:39:16,833
{\an1}and not just by triggering
star birth.

657
00:39:16,866 --> 00:39:20,966
{\an1}It plunges back and forth
through the Milky Way

658
00:39:21,000 --> 00:39:23,633
{\an1}as the galaxies become enmeshed,

659
00:39:23,666 --> 00:39:27,933
{\an1}which likely contributed to the
formation of the spiral arms.

660
00:39:27,966 --> 00:39:31,933
{\an1}But its influence is
fast fading.

661
00:39:31,966 --> 00:39:34,600
BOSE:
The question as to whether the
Sagittarius Dwarf galaxy

662
00:39:34,633 --> 00:39:37,766
is still around
kind of depends on

663
00:39:37,800 --> 00:39:40,933
{\an1}what you kind of end up thinking
of as being a galaxy,

664
00:39:40,966 --> 00:39:42,700
{\an1}after a certain point.

665
00:39:42,733 --> 00:39:44,466
{\an1}It is really a galaxy that is

666
00:39:44,500 --> 00:39:47,900
{\an1}in the process of being
totally disrupted.

667
00:39:47,933 --> 00:39:49,333
{\an1}And one day it will end up
merging

668
00:39:49,366 --> 00:39:52,000
{\an1}with the center of our galaxy.

669
00:39:52,033 --> 00:39:54,500
{\an1}So in some sense,
it's only the

670
00:39:54,533 --> 00:39:56,600
{\an1}sort of memory of the galaxy
that is left behind.

671
00:39:56,633 --> 00:40:00,600
♪ ♪

672
00:40:00,633 --> 00:40:03,066
NARRATOR:
When we look up
at the night sky,

673
00:40:03,100 --> 00:40:06,866
{\an1}it's easy to think of
the Milky Way as static.

674
00:40:06,900 --> 00:40:11,266
♪ ♪

675
00:40:11,300 --> 00:40:16,433
{\an1}But we now know it's evolved
through a turbulent history

676
00:40:16,466 --> 00:40:20,733
{\an1}of collisions and mergers.

677
00:40:20,766 --> 00:40:24,700
EZZEDDINE:
I think that Gaia opened up this
whole new vision for us.

678
00:40:24,733 --> 00:40:27,300
{\an1}Our Milky Way is not static.

679
00:40:27,333 --> 00:40:32,500
{\an1}It is dynamic and it has such
a rich, dynamic history.

680
00:40:32,533 --> 00:40:35,600
NARRATOR:
But none of it is random.

681
00:40:35,633 --> 00:40:38,866
♪ ♪

682
00:40:38,900 --> 00:40:42,333
{\an1}The force that causes galaxies
to form,

683
00:40:42,366 --> 00:40:47,766
merge,

684
00:40:47,800 --> 00:40:51,166
and evolve

685
00:40:51,200 --> 00:40:54,833
is gravity.

686
00:40:54,866 --> 00:40:56,400
{\an1}The thing that ultimately
sculpts

687
00:40:56,433 --> 00:40:58,266
{\an1}how those galaxies look
is gravity.

688
00:40:58,300 --> 00:41:02,166
♪ ♪

689
00:41:02,200 --> 00:41:03,566
{\an1}It's not the collisions.

690
00:41:03,600 --> 00:41:09,066
{\an1}It's the stars within those
galaxies tugging on one another.

691
00:41:09,100 --> 00:41:11,533
{\an7}And it's the underlying
dark matter halos

692
00:41:11,566 --> 00:41:14,000
{\an7}of those galaxies
merging together.

693
00:41:14,033 --> 00:41:17,800
♪ ♪

694
00:41:23,133 --> 00:41:26,433
COLLINS:
So we're actually at a really
exciting time now in astronomy.

695
00:41:26,466 --> 00:41:28,133
{\an1}Because we can tell the story

696
00:41:28,166 --> 00:41:30,366
{\an1}not only of how our galaxy
came to be,

697
00:41:30,400 --> 00:41:31,900
{\an1}and how everything led up
to now,

698
00:41:31,933 --> 00:41:33,933
{\an1}but we can also start to peer
into the future

699
00:41:33,966 --> 00:41:35,866
{\an1}and see what's in store,
what's yet to come

700
00:41:35,900 --> 00:41:37,766
{\an1}for the evolution of our galaxy.

701
00:41:37,800 --> 00:41:42,100
♪ ♪

702
00:41:51,400 --> 00:41:54,300
NARRATOR:
The more we learn about
the Milky Way

703
00:41:54,333 --> 00:41:58,433
{\an1}and its dynamic history,

704
00:41:58,466 --> 00:42:03,466
{\an1}the more incredible
it seems that we ourselves,

705
00:42:03,500 --> 00:42:06,533
{\an1}orbiting just one star
among billions,

706
00:42:06,566 --> 00:42:13,233
{\an1}have been able to figure out
our galaxy's story,

707
00:42:13,266 --> 00:42:14,833
{\an1}written in the stars.

708
00:42:14,866 --> 00:42:17,233
♪ ♪

709
00:42:17,266 --> 00:42:24,233
{\an1}And we are now poised
to map out its ultimate fate.

710
00:42:27,966 --> 00:42:32,166
GUPTA:
The Milky Way is no stranger
to galactic collisions.

711
00:42:32,200 --> 00:42:34,100
{\an7}As we look around the night sky,

712
00:42:34,133 --> 00:42:36,066
{\an7}we see evidence that our
Milky Way galaxy

713
00:42:36,100 --> 00:42:38,700
{\an7}has had these interactions
with galaxies before,

714
00:42:38,733 --> 00:42:40,533
{\an1}but what's coming next
is something

715
00:42:40,566 --> 00:42:41,900
{\an1}on an entirely different scale.

716
00:42:41,933 --> 00:42:46,000
{\an1}This faint smudge of light
that you see right there

717
00:42:46,033 --> 00:42:47,700
{\an1}in the center of the image,

718
00:42:47,733 --> 00:42:49,633
{\an1}it's not some condensation
on the lens

719
00:42:49,666 --> 00:42:51,566
{\an1}or a cloud in the sky above us.

720
00:42:51,600 --> 00:42:55,666
{\an1}This is an entire other galaxy,
a huge galaxy,

721
00:42:55,700 --> 00:42:58,733
{\an1}two-and-a-half million
light years away from us.

722
00:42:58,766 --> 00:43:00,033
{\an1}To put that into units

723
00:43:00,066 --> 00:43:01,833
{\an1}that humans can try to
understand,

724
00:43:01,866 --> 00:43:04,533
{\an1}this faint smudge of light
is about

725
00:43:04,566 --> 00:43:06,900
{\an1}15 billion billion miles away.

726
00:43:06,933 --> 00:43:09,500
♪ ♪

727
00:43:10,666 --> 00:43:14,300
NARRATOR:
This galaxy is called Andromeda.

728
00:43:14,333 --> 00:43:16,266
♪ ♪

729
00:43:16,300 --> 00:43:21,200
{\an1}And is set to play a defining
role in our galaxy's future.

730
00:43:23,666 --> 00:43:25,633
{\an1}The Hubble Space Telescope

731
00:43:25,666 --> 00:43:29,066
{\an1}has taken extraordinary images
of Andromeda.

732
00:43:29,100 --> 00:43:31,433
♪ ♪

733
00:43:31,466 --> 00:43:34,266
{\an1}Compared to the disk of the
Milky Way,

734
00:43:34,300 --> 00:43:37,500
{\an1}Andromeda seems tiny,

735
00:43:37,533 --> 00:43:41,033
when in fact,
it's anything but.

736
00:43:41,066 --> 00:43:47,900
♪ ♪

737
00:43:47,933 --> 00:43:51,533
{\an1}It's our largest neighbor
in the local group.

738
00:43:55,000 --> 00:44:00,833
{\an1}With the same spiral structure
and the same long history

739
00:44:00,866 --> 00:44:04,233
{\an1}of feeding on smaller galaxies.

740
00:44:04,266 --> 00:44:09,166
♪ ♪

741
00:44:09,200 --> 00:44:11,600
GUPTA:
This image right here
is actually ridiculous

742
00:44:11,633 --> 00:44:13,133
{\an1}when you think about it.

743
00:44:13,166 --> 00:44:15,866
{\an1}It's an observation of part
of the Andromeda galaxy

744
00:44:15,900 --> 00:44:18,033
taken with the
Hubble Space Telescope,

745
00:44:18,066 --> 00:44:21,466
{\an1}and the level of detail here
is incredible.

746
00:44:21,500 --> 00:44:25,800
{\an1}This image contains about
100 million stars

747
00:44:25,833 --> 00:44:28,400
that we can see
in another galaxy.

748
00:44:28,433 --> 00:44:29,533
{\an1}It's just mind-blowing.

749
00:44:29,566 --> 00:44:32,066
{\an1}When we look at it,

750
00:44:32,100 --> 00:44:34,800
{\an1}we start to be able to
understand its structure.

751
00:44:34,833 --> 00:44:39,333
{\an1}And what strikes me immediately
is that it's kind of familiar.

752
00:44:39,366 --> 00:44:41,433
{\an1}If you zoom in on the
spiral arm,

753
00:44:41,466 --> 00:44:42,666
{\an1}it's exactly the same as what
we see

754
00:44:42,700 --> 00:44:43,833
{\an1}when we look into our own
Milky Way.

755
00:44:43,866 --> 00:44:46,800
{\an1}And when we look at the
Andromeda galaxy,

756
00:44:46,833 --> 00:44:49,833
{\an1}we see this history,
we see that

757
00:44:49,866 --> 00:44:52,033
{\an1}it's been cannibalizing these
satellite galaxies

758
00:44:52,066 --> 00:44:54,233
{\an1}in a similar way to the
Milky Way,

759
00:44:54,266 --> 00:44:55,933
{\an1}growing into this beast,
this giant

760
00:44:55,966 --> 00:44:58,333
that's a match
for our own galaxy.

761
00:44:58,366 --> 00:45:03,233
{\an8}♪ ♪

762
00:45:03,266 --> 00:45:06,366
{\an8}COLLINS:
We now have many beautiful
images of Andromeda.

763
00:45:06,400 --> 00:45:08,966
{\an1}We've studied it with a huge
range of telescopes,

764
00:45:09,000 --> 00:45:11,033
{\an1}and in many ways, you know,
it's a lot like the Milky Way,

765
00:45:11,066 --> 00:45:12,400
{\an1}this beautiful spiral galaxy.

766
00:45:12,433 --> 00:45:15,666
{\an1}So you might think that they're,
you know, going to be

767
00:45:15,700 --> 00:45:18,600
{\an1}very similar galaxies
with a very similar history.

768
00:45:18,633 --> 00:45:21,200
{\an1}But what we've learnt through
studying Andromeda over time

769
00:45:21,233 --> 00:45:23,333
{\an1}is that actually,
they're not quite the same.

770
00:45:23,366 --> 00:45:26,500
♪ ♪

771
00:45:26,533 --> 00:45:32,433
NARRATOR:
In fact, Andromeda is 50% bigger
than the Milky Way.

772
00:45:32,466 --> 00:45:36,133
{\an1}And that's not all.

773
00:45:36,166 --> 00:45:39,566
GUPTA:
The Andromeda galaxy
is actually heading towards us

774
00:45:39,600 --> 00:45:44,366
{\an1}at about 250,000 miles per hour.

775
00:45:44,400 --> 00:45:47,133
{\an1}In about four-and-a-half billion
years' time,

776
00:45:47,166 --> 00:45:49,800
{\an1}that faint smudge of light
we saw in the sky

777
00:45:49,833 --> 00:45:52,133
{\an1}will collide with
the Milky Way galaxy,

778
00:45:52,166 --> 00:45:54,933
{\an1}changing our galaxy forever.

779
00:45:54,966 --> 00:46:00,900
♪ ♪

780
00:46:06,566 --> 00:46:09,166
NARRATOR:
The Milky Way as we know it
today

781
00:46:09,200 --> 00:46:14,000
is not eternal.

782
00:46:14,033 --> 00:46:19,333
{\an1}And Earth will witness
the final act.

783
00:46:22,700 --> 00:46:28,100
♪ ♪

784
00:46:28,133 --> 00:46:33,633
{\an1}Two galaxies in a single sky,

785
00:46:33,666 --> 00:46:39,233
{\an1}gradually, but inevitably,
merging into one.

786
00:46:39,266 --> 00:46:42,500
EZZEDDINE:
There is absolute evidence
that Andromeda

787
00:46:42,533 --> 00:46:46,200
{\an1}is going to collide with the
Milky Way one day,

788
00:46:46,233 --> 00:46:49,166
{\an1}because they are pulling each
other closer

789
00:46:49,200 --> 00:46:50,700
{\an1}and closer over time,
and one day,

790
00:46:50,733 --> 00:46:52,866
{\an1}they're just gonna come so close
that they will collide.

791
00:46:52,900 --> 00:46:54,600
♪ ♪

792
00:46:54,633 --> 00:46:56,366
ROSARIO:
Andromeda and the Milky Way,

793
00:46:56,400 --> 00:46:58,866
{\an7}when they come together,
sparks fly.

794
00:46:58,900 --> 00:47:02,100
{\an8}COLLINS:
It's going to be
an incredible time.

795
00:47:02,133 --> 00:47:05,566
{\an7}If we were able to view
this collision happening,

796
00:47:05,600 --> 00:47:08,233
{\an7}it would be amazing to watch
the night sky change over time.

797
00:47:08,266 --> 00:47:11,033
{\an8}♪ ♪

798
00:47:11,066 --> 00:47:12,733
{\an8}GILMORE:
It'd be a really nice sight,
actually.

799
00:47:12,766 --> 00:47:14,700
{\an7}You know, just watch it coming.

800
00:47:14,733 --> 00:47:15,733
{\an7}I mean, there's nothing
you can do about it

801
00:47:15,766 --> 00:47:17,233
{\an8}except sit back
and enjoy the view.

802
00:47:17,266 --> 00:47:21,433
{\an8}♪ ♪

803
00:47:21,466 --> 00:47:25,100
{\an8}COLLINS:
We'll end up smashing these
two galaxies together.

804
00:47:25,133 --> 00:47:28,566
♪ ♪

805
00:47:28,600 --> 00:47:31,533
{\an1}There may be a huge burst
of star formation initially,

806
00:47:31,566 --> 00:47:34,133
{\an1}which will sort of light up the
night sky with fireworks.

807
00:47:34,166 --> 00:47:38,300
♪ ♪

808
00:47:38,333 --> 00:47:39,800
{\an7}And then over time,
that will sort of

809
00:47:39,833 --> 00:47:42,733
{\an7}burn off all the remaining gas
we have in those two galaxies.

810
00:47:42,766 --> 00:47:46,933
♪ ♪

811
00:47:52,700 --> 00:47:56,000
NARRATOR:
But unlike in previous
collisions,

812
00:47:56,033 --> 00:48:00,733
{\an1}this time, our galaxy is the
smaller of the two.

813
00:48:00,766 --> 00:48:05,800
♪ ♪

814
00:48:10,966 --> 00:48:13,300
{\an1}Andromeda and the Milky Way

815
00:48:13,333 --> 00:48:17,033
{\an1}pull at each other's
spiral arms...

816
00:48:24,566 --> 00:48:27,266
{\an1}Scattering stars...

817
00:48:29,200 --> 00:48:34,900
{\an1}Until no trace of the original
structures remain.

818
00:48:34,933 --> 00:48:39,766
♪ ♪

819
00:48:39,800 --> 00:48:43,600
{\an1}Two spiral galaxies,

820
00:48:43,633 --> 00:48:48,100
{\an1}merged into one colossal mass
of stars.

821
00:48:53,566 --> 00:48:55,400
TREMBLAY:
Watching the motion of galaxies

822
00:48:55,433 --> 00:48:59,000
{\an1}is like looking at a really,
really exquisite ballet

823
00:48:59,033 --> 00:49:01,366
{\an1}in really, really slow motion.

824
00:49:01,400 --> 00:49:04,033
When that dance
is finally complete,

825
00:49:04,066 --> 00:49:07,266
{\an1}the structure of the Milky Way
will be forever altered.

826
00:49:07,300 --> 00:49:09,833
COLLINS:
While this collision will
extinguish the Milky Way

827
00:49:09,866 --> 00:49:11,066
{\an1}and Andromeda as we know them,

828
00:49:11,100 --> 00:49:13,766
{\an1}it will also create
a whole host of new stars,

829
00:49:13,800 --> 00:49:16,500
{\an1}and around those new stars,
there'll be new planets,

830
00:49:16,533 --> 00:49:18,266
{\an1}and maybe another generation
of people

831
00:49:18,300 --> 00:49:20,400
{\an1}asking the same questions
that we're asking now.

832
00:49:20,433 --> 00:49:22,066
{\an1}Where have they come from?

833
00:49:22,100 --> 00:49:23,666
{\an1}What's their place in the
galaxy?

834
00:49:23,700 --> 00:49:26,133
{\an1}And what's going to happen
in their future?

835
00:49:26,166 --> 00:49:28,300
ROSARIO:
We will not be able to see the
beautiful galaxy

836
00:49:28,333 --> 00:49:31,700
{\an1}that we see right now,
but the universe will carry on.

837
00:49:31,733 --> 00:49:37,233
♪ ♪

838
00:49:41,133 --> 00:49:45,066
NARRATOR:
As we look even deeper
into the future,

839
00:49:45,100 --> 00:49:48,333
{\an1}all of the galaxies in our
local group

840
00:49:48,366 --> 00:49:53,733
{\an1}will eventually merge into one
enormous entity.

841
00:49:56,800 --> 00:49:59,833
{\an1}Floating in isolation.

842
00:49:59,866 --> 00:50:03,800
♪ ♪

843
00:50:03,833 --> 00:50:06,966
{\an1}As the universe expands,

844
00:50:07,000 --> 00:50:12,266
{\an1}the distance between all the
galactic groups will increase

845
00:50:12,300 --> 00:50:17,233
{\an1}and the other galaxies will
simply disappear from view.

846
00:50:17,266 --> 00:50:22,366
♪ ♪

847
00:50:22,400 --> 00:50:24,833
COLLINS:
Knowing that we can sort of
look into the future

848
00:50:24,866 --> 00:50:26,933
{\an1}many billions of years
and understand

849
00:50:26,966 --> 00:50:29,166
{\an1}what will happen to our galaxies
is mind-blowing.

850
00:50:29,200 --> 00:50:30,833
♪ ♪

851
00:50:30,866 --> 00:50:34,200
NARRATOR:
And all of this
we have determined

852
00:50:34,233 --> 00:50:38,700
{\an1}by looking up at the skies from
one tiny,

853
00:50:38,733 --> 00:50:43,200
{\an1}unremarkable outpost in the
Milky Way.

854
00:50:43,233 --> 00:50:48,100
BOSE:
Even though we as humans have
such an insignificant role

855
00:50:48,133 --> 00:50:50,100
{\an1}in the grand scheme of things,

856
00:50:50,133 --> 00:50:52,833
{\an7}there is so much about the
vastness of space

857
00:50:52,866 --> 00:50:55,300
{\an7}that we can understand just
from our

858
00:50:55,333 --> 00:50:57,666
{\an1}unique perspective here on
Earth.

859
00:50:57,700 --> 00:51:00,233
♪ ♪

860
00:51:00,266 --> 00:51:02,533
TREMBLAY:
Earth is a tiny little rock

861
00:51:02,566 --> 00:51:06,333
{\an7}in a really indescribably vast
cosmic ocean, right?

862
00:51:06,366 --> 00:51:10,566
{\an7}We are just a tiny little planet
spinning in the void.

863
00:51:10,600 --> 00:51:15,800
NARRATOR:
But the story of our night sky
is far from being complete.

864
00:51:15,833 --> 00:51:21,100
{\an1}And there is so much more
to discover.

865
00:51:21,133 --> 00:51:24,333
ROSARIO:
Is there life in the universe?

866
00:51:24,366 --> 00:51:26,833
{\an1}And has there been life in the
universe

867
00:51:26,866 --> 00:51:27,933
{\an1}from the very beginning?

868
00:51:27,966 --> 00:51:30,500
♪ ♪

869
00:51:30,533 --> 00:51:32,566
EZZEDDINE:
What is dark matter?

870
00:51:32,600 --> 00:51:33,633
{\an1}What is dark energy?

871
00:51:33,666 --> 00:51:35,933
{\an7}How does it affect our universe?

872
00:51:35,966 --> 00:51:38,700
{\an7}Particularly, how does it affect
our Milky Way

873
00:51:38,733 --> 00:51:40,333
{\an7}and even our own solar system?

874
00:51:40,366 --> 00:51:42,933
♪ ♪

875
00:51:42,966 --> 00:51:46,100
IMARA:
We want to know where
we come from.

876
00:51:46,133 --> 00:51:50,433
{\an1}We want to understand
our origins and our destiny.

877
00:51:50,466 --> 00:51:53,166
{\an7}And also, we just love
a good story.

878
00:51:53,200 --> 00:51:54,533
{\an8}We love mystery.

879
00:51:54,566 --> 00:51:56,533
{\an7}And the story of the
universe is

880
00:51:56,566 --> 00:51:59,066
{\an1}the greatest story of all.

881
00:51:59,100 --> 00:52:05,433
♪ ♪

882
00:52:27,500 --> 00:52:32,466
{\an8}♪ ♪

883
00:52:32,500 --> 00:52:34,733
{\an8}ALOK PATEL:
Discover the science
behind the news

884
00:52:34,766 --> 00:52:36,566
{\an7}with the "NOVA Now" podcast.

885
00:52:36,600 --> 00:52:39,733
{\an7}Listen at pbs.org/novanowpodcast

886
00:52:39,766 --> 00:52:42,566
{\an7}or wherever you find your
favorite podcasts.

887
00:52:42,600 --> 00:52:47,233
{\an8}ANNOUNCER:
To order the five-part "NOVA:
Universe Revealed" on DVD,

888
00:52:47,266 --> 00:52:51,266
{\an8}visit ShopPBS
or call 1-800-PLAY-PBS.

889
00:52:51,300 --> 00:52:56,166
{\an7}Also available with PBS Passport
and on Amazon Prime Video.

890
00:52:56,200 --> 00:53:02,266
{\an8}♪ ♪

891
00:53:14,533 --> 00:53:19,100
{\an8}♪ ♪