(Astronomi) In astronomy, a bulge or galactic bulge is a tightly packed group of stars within a larger formation. The term almost exclusively refers to the central group of stars found in most spiral galaxies (see Galactic spheroid). Bulges were historically thought to be elliptical galaxies that happen to have a disk of stars around them, but high resolution images using the Hubble Space Telescope have revealed that many bulges have properties that are more like spiral galaxies. It is now thought that there are at least two types of bulges, bulges that are like ellipticals and bulges that are like spiral galaxies