Astronomers identify numerous types of dwarf galaxies, based on their shape and composition.
A 2007 paper[8] has suggested that many dwarf galaxies were created by galactic tides during the early evolutions of the Milky Way and Andromeda.
Streams of galactic material are pulled away from the parent galaxies and the halos of dark matter that surround them.
[9] A 2018 study suggests that some local dwarf galaxies formed extremely early, during the Dark Ages within the first billion years after the Big Bang.
Because they are composed of star clusters, BCD galaxies lack a uniform shape.
[28] It is theorised 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.
An extreme example of UCD is M60-UCD1, about 54 million light years away, which contains approximately 200 million solar masses within a 160 light year radius; the stars in its central region are packed 25 times more densely than stars in Earth's region in the Milky Way.
[36] Based on stellar orbital velocities, two UCD in the Virgo Cluster are claimed to have supermassive black holes weighing 13% and 18% of the galaxies' masses.