Active Galaxies

Black holes give rise to many remarkable phenomena such as extragalactic quasars and, in our own Galaxy, microquasars. These objects can be prodigiously luminous across the whole electromagnetic spectrum. Matter can be ejected from the vicinity of black holes and so they can be responsible for imparting significant amounts of heat and energy to their surroundings, way beyond their event horizons. Sometimes these ejections are in the form of highly collimated jets of plasma, moving at relativistic speeds, sometimes outflows - via winds - are seen to be rather slower and rather less directional.

The plasma lobes fuelled by jets from quasars and radio galaxies are frequently 100s of kpc in extent and can in some cases exceed 1 Mpc. These are particularly rewarding to study at both radio and X-ray energies since these wavebands probe different physical processes that are at play. When the jets are pointed towards Earth, they are termed blazars and studies at Gamma-ray energies are possible.

Active galaxies produce radiation across the entire electromagnetic spectrum, and observations at X-ray energies are able to probe into the innermost regions of the accretion process, revealing a complex environment around the black hole of inflows and outflows, with significant reprocessing of photons through absorption and scattering by circumnuclear gas.