Let's build a galaxy.
We live on a planet in a single solar system
inside a large galaxy made up of 100 billion stars.
A supermassive black hole equal to the weight of a few million
suns anchors the center of our galaxy.
Our universe has hundreds of billions
of galaxies, each containing stars like our sun.
Galaxies range in size from ones with 1,000 stars
to ones with a trillion or more stars.
That means we have a lot of places to explore.
Edwin Hubble was one of the first astronomers
to discover that our universe isn't just sitting still,
but it's expanding.
Hubble also grouped galaxies by how
they looked because not all galaxies are the same.
He described a few distinct types, elliptical galaxies,
which have no easily defined shape
with stars that move chaotically and spirals
or disk galaxies, which are flat with pinwheel spiral arms that
spread out from the center.
As Hubble began to classify galaxies,
he quickly discovered many galaxies didn't fit neatly
into his categories.
Was it possible that galaxies change from one type
to another over eons?
Even our own Milky Way galaxy has been changing.
There are a handful of smaller galaxies,
such as the Magellanic Clouds, Fornax, Sculptor, Leo
and others that orbit around us.
The powerful gravity of the Milky Way
affects these nearby galaxies either causing
them to be ripped apart or pulling them
into merge with ours.
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Astronomers can tell if a star has invaded
from one of these nearby galaxies
if it lacks certain elements that
are formed by many generations of star birth
and star death within the Milky Way itself.
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The Milky Way has been a star factory
for about 10 billion years.
Generations of stars have fused hydrogen and helium gas
to heavier elements such as metals within their cores
and then spewed these metals out into the galaxy.
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This process enriches the gas and promotes
the future generations of stars like our own sun.
Many of the stars in the galaxies are around
ours do not have the heavier elements
in such abundance because of their different history.
So we can tell which stars originated in the Milky Way
and which ones joined our galaxy later.
The Milky Way and its nearest similarly
sized neighbor Andromeda, or M31 are part
of a local group of galaxies.
They're pretty close to each other.
Only about 10 galaxy links separate the Milky Way
and Andromeda.
And when they collide in 4 billion years,
it will be spectacular.
We can simulate the collision of the Milky Way and Andromeda
galaxies and predict that it should
lead to a great deal of new stars
and a whole lot of galactic chaos.
Eventually, the two galaxies will
merge into a single galaxy, which
will settle down into a larger Milkdromeda Galaxy.
But don't worry.
The stars within the galaxies won't collide.
Galaxies are made up of mostly empty space.
And the stars within them are very spread out.
But the gas that surrounds the stars and forms them
will collide spectacularly.
Many galaxies are in the middle of a collision today.
These type of galaxies are the ones
that would not have fit into Edwin Hubble's categories,
irregularly shaped spirals, merging and distorting
arms winding and strangely beautiful shapes.
The exquisite detail of these types of collisions
can be studied in a new light with NASA's James Webb Space
Telescope.
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See those blue galaxies in this picture taken
by the Hubble Space Telescope?
Those are star factories making stars
at a much faster rate than the red ones.
Webb can track the production of the heavier stellar elements
in ways that no previous telescope could.
Webb's infrared eyes can see through the dust
in the galaxies to more clearly study
the formation of new stars.
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While stars within the galaxies are spread out,
the galaxies themselves tend to clump
in nodes where gravity draws matter together.
Galaxies are connected to each other
by web like strands of gas and dark matter.
Galaxies most often form where the dark matter
strands intersect.
This cosmic web is the scaffolding
that supports galaxy formation.
Dark matter is five times more abundant than visible matter
in the universe.
Astronomers have simulated the spider web of dark matter
by using the visible distribution of galaxies today.
But Webb will allow us to see farther into the distant past
to galaxies just after they were first born.
During this earlier time, the universe was hotter and denser.
And many more stars formed in the early generations
of galaxies.
We're already late to the party.
The best time for making stars was about 10 billion years ago.
With Webb, we can look back to the early days of galaxies
and stars and follow the trail of clues
to understand the formation of these heavy elements, carbon,
oxygen, nitrogen, silicon, and others
that make life possible today.
Webb will also allow us to study the collision of early galaxies
and give us new clues about the invisible but dominant
dark matter in the early universe.
And maybe one of those spirals out there in the distance back
in time about 10 billion years could
be a mirror image of our own Milky Way looking back at us.
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