Blue Compact Dwarf Galaxies
In astronomy, a blue compact dwarf galaxy (BCD galaxy) is a small galaxy which contains large clusters of young, hot, massive stars. These stars cause the galaxy to appear blue in color. Since they exist mostly in clusters, blue compact dwarf galaxies don't have an exact uniform shape. They consume gas intensely, which causes their stars to become very violent when they are forming.
Blue compact dwarf galaxies cool in the process of forming new stars. Their stars are all formed at different time periods, so the galaxies have time to cool and to build up matter to form new stars.
The galaxies aren't blue throughout - they actually have a lot of stars of different colors. But throughout them there are a lot of star-forming regions in which the most massive and brightest stars are blue. Since these stars greatly outshine their neighbors, the combined light from these galaxies appears blue from far away.
As time passes, blue compact dwarf galaxies change shape due to star formation.
Nearby examples include NGC 1705, NGC 2915 and NGC 3353.
Read more about this topic: Blue Compact Dwarf Galaxy
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