Dwarf galaxies are the most abundant type of galaxy in the universe but are difficult to detect due to their low luminosity, low mass and small size. They are most commonly found in galaxy clusters, often as companions to larger galaxies, and are classified into three main types:
An extreme type of Dwarf Irregular galaxy which features bursts of concentrated star formation are the Blue Compact Dwarfs. These galaxies contain large amounts of gas and are currently undergoing vigourous star formation resulting in their unusually blue colour. They generally have diameters less than 3 kiloparsecs and about 109 solar masses of material.