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What is a Galaxy?

Definition

A galaxy is a vast collection of gas, dust, and billions of stars and their solar systems. Galaxies are held together by gravity and can range in size from a few million to trillions of stars.

Structure

Galaxies are typically composed of a central bulge of stars, a surrounding disk of stars and gas, and a halo of dark matter. The Milky Way galaxy, which contains our solar system, is a barred spiral galaxy with a central bulge, a disk of stars and gas, and a halo of dark matter.

Types of Galaxies

There are many different types of galaxies, including elliptical galaxies, spiral galaxies, and irregular galaxies. Elliptical galaxies are round or oval in shape and have little or no gas and dust. Spiral galaxies have a central bulge surrounded by a disk of stars and gas. Irregular galaxies have no regular shape and often contain a lot of gas and dust.

Formation and Evolution

Galaxies are thought to form from the collapse of large clouds of gas and dust. As the cloud collapses, it begins to rotate and flatten into a disk. The stars in the galaxy then form from the gas and dust in the disk.

Galaxy Clusters

Galaxies often cluster together in groups called galaxy clusters. Galaxy clusters can contain hundreds or even thousands of galaxies. The Virgo Cluster, which contains the Milky Way galaxy, is one of the largest galaxy clusters in the universe.

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