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.
During the epoch of reionization the first stars and black holes in the Universe (re-) ionized the Intergalactic Medium. Studying the epoch of reionization will tell us about the first galaxies.
Observations of nearby galaxies and high-redshift quasars suggest that black holes are present in the majority of galaxies. The first quasars harbor already black holes as massive as several billion solar masses.
Quasars are the most luminous objects in the Universe and powered by accreting supermassive black holes in the centres of galaxies.
The intergalactic medium (IGM) and not galaxies contain most of the baryons (e.g. H, He, C, N, O) in the Universe. We use spectroscopic observations of high redshift backgound quasars to study this material.
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.