Speaker
Description
When a black hole rings due to some external perturbation it emits gravitational waves described by quasi normal modes (QNMs) – a series of exponentially damped harmonic oscillations. If the final state is fully described by the Kerr(-Newman) metric, this ring-down carries a unique signature of its parameters encoded in the modes' complex frequencies. However, astrophysical black holes are rarely isolated. Due to attraction forces, black holes bound matter from their environment, often resulting in the formation of disc-like structures. I present our work, where we studied the quasinormal modes of a black hole surrounded by gravitating thin disc. We found that within the physical parameter space, the presence of the disc universally reduces oscillating frequencies while prolonging dumping time. If such a universal relation holds generically, it may help distinguish shifts in quasinormal modes caused by environmental effects (such as the presence of an accretion disc) from those predicted by other putative effects from theories beyond GR.
