Galaxies

Part of Hall of the Universe.

Galaxies_HERO AMNH/D. Finnin

Galaxies are the basic building blocks of the universe. Even in a tiny patch of sky, many hundreds can be seen. By surveying such regions, astronomers estimate that there may be 100 billion galaxies in the observable universe. These galaxies are not uniformly spread through space — they commonly occur in pairs, groups, clusters, and superclusters.

In This Section

Exhibit What is a Galaxy? Galaxies are titanic swarms of tens of millions to trillions of stars, orbiting around their common center of gravity. Exhibit Gravity and Rotation Everything in a galaxy orbits around the galaxy’s center. Exhibit Spiral Galaxies Spiral galaxies have three visible parts: a disk of stars; a central bulge of older stars; and a halo of the oldest stars. Exhibit Elliptical Galaxies Elliptical galaxies have smooth, rounded shapes because the orbits of their stars are oriented in all directions. Exhibit Irregular Galaxies Irregular galaxies have a chaotic appearance, and are usually small. Exhibit Other Galaxy Classifications The classification of galaxies by shape relies upon images made with visible light. Exhibit Formation and Evolution of Galaxies In the early universe, there were no galaxies. Today, there are many billions. How did they form? Exhibit Interacting Galaxies When galaxies pass close to each other or collide, gravity pulls them apart, twisting and distorting their shapes. Exhibit The Milky Way and Its Neighbors The Milky Way Galaxy resides in a neighborhood of a few dozen galaxies called the Local Group.