dwarf galaxy

The term dwarf galaxy is used for galaxies much smaller than the Milky Way, i.e., of a few billion stars at most and as small as 100 parsecs across. They can be any of the normal galaxy types (dwarf elliptical, dwarf irregular, dwarf spiral) or a dwarf spheroidal galaxy, more sphere-shaped, like a typical globular cluster but more extensive (and perhaps containing multiple globular clusters), and dwarf galaxy classifications have been defined. Many known dwarf galaxies are satellite galaxies. Additional specific terms:

• blue compact dwarf galaxy (BCD or blue compact galaxy or BCG) - with young hot stars.
• ultra-compact dwarf galaxy (UCD) - a width in the 100-parsec range.
• hobbit galaxy - small, faint dwarf galaxy.

(The term compact galaxy (CG) came into use meaning it has a high surface brightness compared to its apparent diameter, which can be the result of a very high density of stars.)

Example dwarf galaxies in the Local Group:

• Canis Major Dwarf Galaxy
• Large Magellanic Cloud (sometimes so-classified)
• Small Magellanic Cloud
• Sagittarius Dwarf Irregular Galaxy
• Sagittarius Dwarf Elliptical Galaxy
• Triangulum II
• Ursa Major II Dwarf
• Wolf-Lundmark-Melotte

Beyond the Local Group:

• I Zwicky 18
• Haro 29
• SBS 0335-052

Note that the abbreviation BCG is also used for brightest cluster galaxy.