Dwarf galaxy

Image of the Phoenix Dwarf Galaxy

A dwarf galaxy is a small galaxy composed of up to several billion stars, a small number compared to our own Milky Way's 200-400 billion stars. The Large Magellanic Cloud, containing over 30 billion stars, is sometimes classified as a dwarf galaxy while others consider it a full-fledged galaxy going around the Milky Way galaxy.

Local dwarfs

There are many dwarf galaxies in the Local Group: these small galaxies frequently orbit around larger galaxies, such as the Milky Way, the Andromeda Galaxy and the Triangulum Galaxy. A recent paper ^[1] has suggested that many dwarf galaxies were created by tidal forces during the early evolution of the Milky Way and Andromeda.

The Milky Way has 14 known dwarf galaxies orbiting it, and recent discoveries^{[citation needed]} have also led astronomers to believe the largest globular cluster in the Milky Way, Omega Centauri, is in fact the core of a dwarf galaxy with a black hole in its center,^[2] which was at some time absorbed by the Milky Way. (See Milky Way for more information.)

Dwarf galaxies

Dwarf galaxies come in many different morphologies:

Elliptical galaxy: dwarf elliptical galaxy (dE) and its subtype dwarf spheroidal galaxy (dSph)
Irregular galaxy: dwarf irregular galaxy (dI)
Spiral galaxy: dwarf spiral galaxy

Hobbit galaxies

The recently coined term, hobbit galaxy has been used to describe galaxies smaller and dimmer than dwarf galaxies.^[3]^[4]

Ultra Compact Dwarfs

Ultra Compact Dwarf galaxies (UCD) are a recently discovered class of very compact galaxies with very high stellar population counts. They are thought to be on the order of 200 light years across, with a hundred million stars. ^[5] It is theorized that these are the cores of nucleated dwarf elliptical galaxies, that have been stripped of gas and outlying stars by tidal interactions, travelling through the hearts of rich clusters. ^[6] UCDs have been found in the Virgo Cluster, Fornax Cluster, Abell 1689, amongst other clusters. ^[7]