In astronomy, a bulge is a tightly packed group of stars. The term almost exclusively refers to the central group of stars found in most spiral galaxies. Bulges were historically thought to be elliptical galaxies that happen to have a disk of stars around them. Yet, high resolution images, using Hubble Space Telescope reveal 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.