The richness and complexity of these images provided an impetus for theoretical investigations, especially numerical simulations of how clusters form and grow, as well as detailed optical and radio studies of clusters. The Einstein Observatory provided the first detailed X-ray images of the structure and morphology of clusters of galaxies. The Einstein Observatory, followed by ROSAT, offered the first opportunities to image the X-ray sky using focusing optics (see Van Speybroeck ), which significantly increased our knowledge of both galactic and extragalactic X-ray sources.

Thus, the X-ray emission from the ICM provides a sensitive tool for mapping both the mass distribution of the hot gas, as well as the distribution of the total mass, which is primarily dark matter in groups and clusters. The hot intracluster medium (ICM) is gravitationally the dominant luminous baryonic component in clusters. ROSAT observations were used to make the first detection of cavities in the hot gas around NGC1275.ĮINSTEIN OBSERVATORY | RESEARCH & SELECTED PUBLICATIONSĬlusters of galaxies have been a focus of X-ray astronomical research since the discovery that they were luminous X-ray sources (Kellogg, Gursky, Leong, Schreier, Tananbaum, Giacconi, 1971, ApJ Letters 165, L49 | Gursky, Kellogg, Leong, Tananbaum, Giacconi, 1971, ApJ Letters L43 | Forman, Kellogg, Gursky, Tananbaum, Giacconi, 1972, ApJ 178, 309).

Einstein imaging observations led to 1) the discovery of hot gas halos in early type galaxies and groups that are gravitationally bound by dark matter halos, 2) the identification of multiple mass components in clusters of galaxies ('double' clusters), and 3) showed that 40% of clusters at the present epoch have significant substructures from ongoing mergers and are not relaxed systems.

Hot gas halos ram pressure