BLACK HOLES · Numerical models of black hole systems as sources of gravitational radiation

Final Activity Report Summary - BLACK HOLES (Numerical Models of Black Hole Systems as Sources of Gravitational Radiation)

This project led to a number of important results in the field of the astrophysics of black holes and strongly gravitating systems. Black holes are known to lie at the centres of most galaxies. In about 10 % of these galaxies, known as quasars, the black holes are surrounded by an accretion disk of material that emits light as it falls into the hole. When galaxies merge, the two black holes form a binary that emits gravitational radiation as the holes eventually spiral together and merge. It has been predicted that at the merger, the final black hole can get a kick, possibly ejecting it from the centre of the galaxy along with the accretion disk. At a smaller level, stellar mass black holes and neutron stars can also accrete from a disk of material. These objects are seen as X-ray binaries, and will also emit gravitational radiation as they orbit each other or spin up. This project studied the phenomena of black hole and neutron star systems from a variety of astrophysical viewpoints. It resulted in a number of scientific achievements, among which the two most important were: 1. the non-detection of predicted post-merger black hole kicks, meaning that the predictions of numerical relativity should be refined with additional physics to account for the observations; and 2. the first detection of a neutron star spinning up through consumption of its companion star, which definitely confirmed a missing link between old, rapidly spinning, pulsars and young slowly spinning neutron stars in X-ray binaries. Other results included a suggestion of cosmic evolution in the black hole mass and galaxy size relation as well as the determination of quasar accretion disk colours as a function of their temperature.

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