Galaxies

Galaxies are vast systems of stars, gas, dust, and dark matter bound by gravity.

Types of Galaxies

• Spiral galaxies - Flat disks with spiral arms and a central bulge. Often have ongoing star formation. Examples: Milky Way, Andromeda (M31), Whirlpool (M51).
• Elliptical galaxies - Round or oval, composed mainly of older stars with little gas/dust. Range from dwarf to giant. Example: M87.
• Irregular galaxies - No regular shape, often the result of gravitational interactions. Examples: Large and Small Magellanic Clouds.
• Barred spirals - Spiral galaxies with a bar of stars through the center. The Milky Way is a barred spiral.

The Local Group

Our Milky Way belongs to a small cluster of about 50 galaxies called the Local Group. The Andromeda Galaxy (M31) and Triangulum Galaxy (M33) are the other major members.

Galaxy Clusters and Superclusters

Galaxies congregate in clusters (tens to thousands of members). Clusters group into superclusters. Our Local Group is part of the Virgo Supercluster, itself part of the larger Laniakea Supercluster.

Galaxy Interactions

Galaxies sometimes collide and merge. In about 4 billion years, the Milky Way and Andromeda will collide and eventually merge into a single giant elliptical galaxy.