Figure 13-40 The Coma Cluster (a) This rich, regular cluster, containing thousands of galaxies, is about 300 million light-years from Earth. Only the inner region of the cluster is shown here. (b) Regular clusters are composed mostly of elliptical and lenticular galaxies and are sources of X-rays. This Chandra image shows Coma’s central region, which is 1.5 million light-years across. The gas cloud emitting most of these X-rays has a temperature of 100 million K.