Black Hole Astrophysics

Black holes are some of the most fascinating objects in the universe. Stellar mass black holes form in stellar binary systems when some of the most massive stars run out of fuel and collapse. Supermassive black holes, with masses from hundreds of thousands to tens of billions times that of our sun, are found in the centres of almost all galaxies. As matter spirals on to a black hole through an accretion disc, it heats up to extreme temperatures and the energy released from this accretion process can be seen across much of the visible universe. Recent observational developments include the Event Horizon Telescope’s stunning image of the innermost regions of the accretion flow around some nearby supermassive black holes, and the detection of gravitational waves from merging stellar mass black holes with LIGO. Future space-based missions will detect the gravitational wave emission from merging supermassive black holes as well. Additionally, the new generation of all-sky monitoring facilities have led to a dramatic increase in the rate of discovery of rapidly varying active galactic nuclei, with outbursts from the central accretion flow seen on timescales ranging from hours to years. These systems, known as quasi-periodic eruptions (QPEs) and repeating nuclear transients (RNTs), are thought to be related to tidal disruption events (TDEs) in which a star passes sufficiently close to the supermassive black hole that it is either partially or completely destroyed by the black hole’s tidal field. The resulting stellar debris forms an accretion flow that powers the emission we see. In Leeds we research many aspects of black hole astrophysics, including: (1) the dynamics of accretion discs and resulting growth of supermassive black holes in galaxy centres, (2) the merging of supermassive black hole binaries and the associated gravitational waves, and (3) the disruption and accretion of stars by supermassive black holes.