The Virgo Cluster
X-ray image of the Virgo cluster of galaxies in the hard band from the ROSAT All-Sky Survey (RASS). This nearby cluster, at a distance of about 20 Mpc, extends over a large region in the sky and can be traced in X-rays in the RASS for about 8 degrees in north-south and 5 degrees in east-west direction. The cluster consist of a compact, X-ray luminous core region centered on M87 and an irregular extended part which shows the cluster as a dynamically young object.
Böhringer, H., U. G. Briel, R. A. Schwarz, W. Voges, G. Hartner, and J. Trümper, The structure of the virgo cluster of galaxies from rosat x-ray images, Nature 368, 828-831 (1994)