Types of Galaxies

Galaxies are concentrations of stars, gas, dust, and dark matter. They come in a variety of shapes and sizes. Some are fated to collide, like the Milky Way and Andromeda.

Astronomers classify galaxies into three major categories: elliptical, spiral and irregular.

Ellipticals, which account for about one-third of galaxies observed, possess comparatively little gas and dust, contain older stars and are not actively forming stars anymore.

Spiral galaxies appear as flat, blue-white disks of stars, gas and dust with yellowish bulges in their centers.

Irregular galaxies, which have very little dust, are neither disk-like nor elliptical. Astronomers often see irregular galaxies as they peer deeply into the universe, which is equivalent to looking back in time. These galaxies are abundant in the early universe, before spirals and ellipticals developed.