Large scale extended X-ray emission from the Virgo cluster of galaxies

HOT, tenuous gas is revealed, by X-ray observations¹, to permeate many clusters of galaxies. If the gas is in hydrostatic equilibrium, it traces the cluster's gravitational potential. X-ray mapping of clusters of galaxies can be used to estimate the total cluster mass, including dark matter, as well as its spatial distribution. Previous observations of X-ray emission from the Virgo cluster, the nearest rich cluster of galaxies, showed it to be concentrated within ~100 arcmin of M87, the dominant galaxy in the cluster^2,3. Because the optical image of the Virgo cluster is ~ 12° in diameter, the X-ray emission was thought to be associated with M87 rather than with the cluster as a whole. Here we report a preliminary mapping of Virgo made by the Ginga satellite which shows the extended X-ray emission as broadly distributed as the cluster's optical extent. This indicates that the galaxies of the Virgo cluster are immersed in a hot diffuse intracluster medium.