The Coma Cluster of galaxies. An optical image (a) shows two giant galaxies near the center plus a number of smaller galaxies. The raw X-ray image (b) was taken by the Chandra X-Ray Observatory. The size of the optical and X-ray fields shown is about 600 kpc (2 million light years). (c) is an overlay of the optical image with a high contrast X-ray image that displays the regions with high X-ray surface brightness around two giant elliptical galaxies that dominate the cluster.
