Galaxy

A galaxy is a gravitationally bound system of stars, stellar remnants, interstellar gas, dust, and dark matter.

A galaxy is a gravitationally bound system of stars, stellar remnants, interstellar gas, dust, and dark matter. Galaxies range from small dwarf systems to enormous collections containing hundreds of billions or even trillions of stars, and they are commonly grouped by shape into spiral, elliptical, and irregular types. The Milky Way is the galaxy that contains the Solar System.

Definition

A galaxy is a system made up of stars and interstellar material bound together by gravity. In addition to visible matter, galaxies contain dark matter, which accounts for most of their mass.

Types of galaxies

Astronomers commonly divide galaxies into spiral, elliptical, and irregular types based on shape and structure. Some sources also recognize lenticular galaxies as a separate category in expanded classification schemes.

Size and structure

Galaxies vary widely in size, from dwarf systems with few stars to giant galaxies with hundreds of billions or trillions of stars. Many have a central bulge, disk, and halo, while spiral galaxies show distinct arms rich in gas and dust.

Location in the universe

Galaxies are often found in clusters and groups, sometimes containing only a few members and sometimes thousands. The Milky Way belongs to the Local Group, a galaxy group that also includes Andromeda.

Observation and classification

Modern galaxy classification developed from Edwin Hubble's work, which organized galaxies mainly by appearance. Galaxy shape can provide clues about stellar populations, gas content, and star formation activity.