Published by the Chandra X-ray Center (CXC) Issue number 10 Chandra News

ness. Each shows a bright central region with symmetrical X-ray cavities. The black contours on the A478 image show the radio emission. Clusters of galaxies are complex, multi-component systems with hundreds of galaxies, a hot (107 to 108 K) intracluster medium (ICM), and dark matter evolving in tightly coupled ways. Clusters are unique because of their size. As the most massive bound objects, clusters are the ultimate manifestations of cosmic structure building. A massive, rich cluster with M total ~ 1015 M forms from a density perturbation of radius ~15 Mpc. On these huge scales, most of the mass is dark. Only a few percent of the mass in clusters lies in the optical galaxies. In rich clusters, most of the luminous baryonic mass is in the hot ICM, which comprises about one fifth of the total mass. Since clusters form from such large volumes of space