According to conventional wisdom, clusters of elderly galaxies settled into retirement long ago. With most of their cold gas already having coalesced into stars, these clusters can no longer make new stars or keep supermassive black holes active.
But astronomers studying the 100 brightest galaxies in the cluster Abell 2104 have found six active supermassive black holes rather than the one they had expected. Paul Martini, John S. Mulchaey, and their collaborators, all of Carnegie Observatories in Pasadena, Calif., examined the cluster with the orbiting Chandra X-ray Observatory. They found several areas with concentrations of high-energy X rays, wh