What Are Galaxies?

 begin quotes from Google AI and the Internet:

Galaxies are vast cosmic systems of stars, gas, dust, and dark matter held together by gravity, containing millions to trillions of stars. They are classified into three main types: spiral (like the Milky Way), elliptical, and irregular. These stellar systems, which can be organized into groups, clusters, and superclusters, form the building blocks of the universe and evolve over billions of years.
 

This video explains what a galaxy is:

59s

Mike Sammartano

YouTube · Oct 22, 2022

What is a Galaxy?

Composition:
A galaxy is made up of stars, stellar remnants, interstellar gas, dust, and dark matter, all bound together by gravity.

Scale:

Galaxies vary in size, from dwarf galaxies with a few hundred million stars to giant ones containing over a trillion stars. 

Formation:

Galaxies form when gravity pulls gas and dust together after the Big Bang, which eventually coalesce into stars and then the larger galactic structures. 

Types of Galaxies

Astronomers classify galaxies into three main categories: 

Spiral Galaxies:
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These resemble pinwheels, with arms of stars, gas, and dust. The Milky Way is an example of a spiral galaxy.

Elliptical Galaxies:

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These are shaped like stretched-out circles or ellipses and contain mostly older stars.

Irregular Galaxies:

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These lack a single common shape and are often among the smallest galaxies observed.

This video shows the different types of galaxies:

51s

Learn the Sky

YouTube · Apr 2, 2022

Galaxies and the Universe

Cosmic Structure:
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Galaxies are part of larger structures known as groups, clusters, and superclusters, which are arranged in the vast cosmic web of matter. 

Evolution:

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Galaxies are not static; they form, grow, and evolve over billions of years, sometimes interacting and merging with other galaxies. 

Home Galaxy:

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Our own solar system is located within the Milky Way galaxy, which is just one of many billions of galaxies in the universe. 

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