Institute for Advanced Study Informal Astrophysics Seminar

NOTE TIME CHANGEThe historic first detection of a gravitational waves from merging black holes came with an unexpected windfall: the first observation of a black hole ringdown. The ringdown of a black hole through damped ``quasinormal'' oscillation modes provides us with a unique measurement of the properties of a black hole. Deviations from General Relativity are imprinted on the spectrum of modes, and there is an unexpected richness in ringdown phenomena even in the case of standard Kerr black holes. In this talk, I will discuss past work on the spectrum of rapidly rotating black holes and their unique ringdown signature. I will also discuss a method for computing the spectrum of black hole spacetimes which are perturbed from Kerr. The application of this method reveals the possibility of a parametric instability in rapidly rotating black holes, and allows for the calculation of quasinormal mode frequencies in weakly charged Kerr-Newman black holes.