(small galaxy with a few billion stars)
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, such as a
Often they are satellite galaxies.
Some more specific terms:
- blue compact dwarf galaxy (BCD or blue compact galaxy or BCG) - with young hot stars.
- ultra-compact dwarf galaxy - 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.)
Examples (in Local Group):
David Dunlap Observatory Catalog (DDO)
dwarf spheroidal galaxy (dSph)
hierarchical assembly of galaxies
I Zwicky 18 (I Zw 18)
Local Group (LG)
low-surface-brightness galaxy (LSB galaxy)
rare designator prefixes
TiNy Titans (TNT)
Triangulum II (Tri II)
ultra-faint dwarf galaxy (UFD)