Clusters of galaxies are the largest objects in the Universe that are held together by their own gravity, and provide great tools for studying the processes that govern AGN feedback.
A major area of research in X-ray astronomy is the accretion of matter on to black holes and neutron stars in the context of AGN and galactic X-ray binaries. Accretion is an energetic process and can give high luminosities.
X-ray astronomy research in Cambridge is carried out by an active X-ray Astronomy group whose research focusses on accretion on to compact objects and the physics of clusters of galaxies.