Galaxy Cluster

Group of galaxies which are mutually gravitationally bound. There are two important types of galaxy clusters: Regular and Irregular Galaxy Clusters. Regular clusters are huge spherical groupings of galaxies with large numbers of galaxies concentrated in their centers. They tend to contain thousands of galaxies and to have many bright elliptical and S0 type galaxies. Irregular clusters are not too centrally condensed with a somewhat non-spherical overall shape. They contain a few to hundreds of galaxies. Our Local Group (below) is an example of an irregular cluster of galaxies.

Image Source: abyss.uoregon.edu

Some or all content above used with permission from J. H. Wittke.