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Let's build a galaxy.

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We live on a planet in
a single solar system

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inside a large galaxy made
up of 100 billion stars.

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A supermassive black hole equal
to the weight of a few million

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suns anchors the
center of our galaxy.

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Our universe has
hundreds of billions

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of galaxies, each containing
stars like our sun.

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Galaxies range in size
from ones with 1,000 stars

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to ones with a
trillion or more stars.

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That means we have a lot
of places to explore.

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Edwin Hubble was one of
the first astronomers

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to discover that our universe
isn't just sitting still,

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but it's expanding.

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Hubble also grouped
galaxies by how

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they looked because not
all galaxies are the same.

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He described a few distinct
types, elliptical galaxies,

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which have no
easily defined shape

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with stars that move
chaotically and spirals

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or disk galaxies, which are flat
with pinwheel spiral arms that

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spread out from the center.

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As Hubble began to
classify galaxies,

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he quickly discovered many
galaxies didn't fit neatly

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into his categories.

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Was it possible that
galaxies change from one type

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to another over eons?

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Even our own Milky Way
galaxy has been changing.

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There are a handful
of smaller galaxies,

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such as the Magellanic
Clouds, Fornax, Sculptor, Leo

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and others that orbit around us.

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The powerful gravity
of the Milky Way

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affects these nearby
galaxies either causing

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them to be ripped
apart or pulling them

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into merge with ours.

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[MUSIC PLAYING]

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Astronomers can tell
if a star has invaded

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from one of these
nearby galaxies

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if it lacks certain
elements that

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are formed by many
generations of star birth

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and star death within
the Milky Way itself.

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[MUSIC PLAYING]

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The Milky Way has
been a star factory

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for about 10 billion years.

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Generations of stars have
fused hydrogen and helium gas

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to heavier elements such as
metals within their cores

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and then spewed these
metals out into the galaxy.

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[MUSIC PLAYING]

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This process enriches
the gas and promotes

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the future generations of
stars like our own sun.

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Many of the stars in
the galaxies are around

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ours do not have
the heavier elements

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in such abundance because
of their different history.

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So we can tell which stars
originated in the Milky Way

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and which ones joined
our galaxy later.

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The Milky Way and
its nearest similarly

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sized neighbor Andromeda,
or M31 are part

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of a local group of galaxies.

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They're pretty
close to each other.

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Only about 10 galaxy links
separate the Milky Way

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and Andromeda.

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And when they collide
in 4 billion years,

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it will be spectacular.

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We can simulate the collision
of the Milky Way and Andromeda

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galaxies and predict
that it should

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lead to a great
deal of new stars

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and a whole lot
of galactic chaos.

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Eventually, the
two galaxies will

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merge into a single
galaxy, which

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will settle down into a
larger Milkdromeda Galaxy.

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But don't worry.

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The stars within the
galaxies won't collide.

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Galaxies are made up
of mostly empty space.

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And the stars within
them are very spread out.

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But the gas that surrounds
the stars and forms them

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will collide spectacularly.

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Many galaxies are in the
middle of a collision today.

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These type of
galaxies are the ones

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that would not have fit into
Edwin Hubble's categories,

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irregularly shaped spirals,
merging and distorting

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arms winding and strangely
beautiful shapes.

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The exquisite detail of
these types of collisions

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can be studied in a new light
with NASA's James Webb Space

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Telescope.

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[MUSIC PLAYING]

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See those blue galaxies
in this picture taken

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by the Hubble Space Telescope?

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Those are star
factories making stars

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at a much faster rate
than the red ones.

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Webb can track the production
of the heavier stellar elements

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in ways that no previous
telescope could.

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Webb's infrared eyes
can see through the dust

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in the galaxies to
more clearly study

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the formation of new stars.

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[MUSIC PLAYING]

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While stars within the
galaxies are spread out,

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the galaxies themselves
tend to clump

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in nodes where gravity
draws matter together.

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Galaxies are connected
to each other

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by web like strands of
gas and dark matter.

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Galaxies most often form
where the dark matter

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strands intersect.

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This cosmic web
is the scaffolding

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that supports galaxy formation.

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Dark matter is five times more
abundant than visible matter

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in the universe.

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Astronomers have simulated
the spider web of dark matter

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by using the visible
distribution of galaxies today.

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But Webb will allow us to see
farther into the distant past

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to galaxies just after
they were first born.

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During this earlier time, the
universe was hotter and denser.

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And many more stars formed
in the early generations

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of galaxies.

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We're already late to the party.

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The best time for making stars
was about 10 billion years ago.

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With Webb, we can look back
to the early days of galaxies

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and stars and follow
the trail of clues

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to understand the formation of
these heavy elements, carbon,

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oxygen, nitrogen,
silicon, and others

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that make life possible today.

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Webb will also allow us to study
the collision of early galaxies

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and give us new clues about
the invisible but dominant

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dark matter in the
early universe.

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And maybe one of those spirals
out there in the distance back

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in time about 10
billion years could

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be a mirror image of our own
Milky Way looking back at us.

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[MUSIC PLAYING]

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