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Are all galaxies the same?
We live on a planet in a single solar system,
inside a large galaxy made up of a hundred 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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