Large clusters of galaxies containing thousands of galaxies were discovered by ROSAT as prominent X-ray sources. In addition to this, very small groups of galaxies were found as X-ray sources in the ROSAT sky map like the group shown here. It was discovered by Ramella, Geller, and Huchra in the CfA galaxy survey and has a distance of about 500 million light years. The picture is an optical sky photography superimposed with brightness contours of X-rays. Both of the bright eliptical galaxies are seen clearly in the centre of the group.
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