X-ray sources and globular clusters

A brief summary of the origin, nature, and evolution of globular clusters is followed by a discussion of the unexpected discovery of X-ray sources in six globular clusters: NGC 1851, 6440, 6624, 6712, and 7078(M 15) by the Uhuru satellite. The properties of the X-rays from globular clusters were found to differ drastically from those of conventional X-ray sources (binary stars). X-ray bursts from NGC 6624 and other sources are discussed. The escape velocity at which matter will leave the cluster is greater than 25 km/sec, while the relaxation time of the clusters is less than 100 million years. These data suggest that capture of matter by a central black hole of about 1000 solar masses might be the cause of the X-ray emission in the globular clusters. This hypothesis would make it possible to account both for the brevity of the X-ray bursts and for their strange behavior in the anonymous globular cluster neighboring on the galactic nucleus.