The Coma Cluster of Galaxies . ... The Coma Cluster of Galaxies pictured above is one of the densest clusters known - it contains thousands of galaxies . Each of these galaxies houses billions of stars - just as our own Milky Way Galaxy does. ... In fact, the Coma Cluster is so big it takes light millions of years just to go from one side to the other! Most galaxies in Coma and other clusters are ellipticals, while most galaxies outside of clusters are spirals. ... NASA Official: Jay Norris. ...