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.
Galaxies provide us with valuable clues on the large scale properties of the Universe in which they are embedded. Equally important, they tell us about the physical processes which are responsible for star formation
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.
Black holes are among the most fascinating phenomena thought to exist in the Universe. A black hole is a region of space in which the gravitational field is so powerful that nothing, not even light, can normally escape.
Sverre Aarseth's research into numerical simulations of many-body (N-body) gravitational interactions has developed into a set of FORTRAN codes which describe the dynamics very closely, and freely downloadable.