Physical Sciences: X-rays from the Coma Cluster of Galaxies

Abstract

THE Coma cluster of galaxies is usually considered to contain insufficient matter in the form of galaxies to be gravitationally bound, but the high degree of symmetry of the cluster, and the presumed age of its galaxies, suggest that the cluster is, in fact, gravitationally bound. It is possible that the missing mass takes the form of ionized intracluster gas, and Woolf¹ has used radio, visible light and X-ray observations to set upper limits for the amount of such matter and, more recently, Turnrose and Rood² have discussed the problems of heating and supporting such a gas against gravitational collapse. We present here new observational evidence of X-ray emission which limits the amount of hot intracluster gas to less than 2 % of that required for gravitational binding.