Title: Superradiant instabilities of asymptotically AdS black holes
Speaker: Stephen Green (AEI)
Abstract: Asymptotically AdS spacetimes with reflecting boundary conditions represent a natural setting for studying superradiant instabilities of rotating or charged black holes. In the first part of this talk, I prove that all asymptotically AdS black holes with ergoregions in 4 or more dimensions are linearly unstable to gravitational perturbations. This proof uses the canonical energy method of Hollands and Wald in a WKB limit. In the second part of the talk, I specialize to Reissner-Nordstrom-AdS black holes, which, in the presence of a charged scalar field, are subject to both the near-horizon and superradiant instabilities. I present a linear mode analysis to study the interplay of these instabilities, as well as numerical simulations of the full nonlinear development. Our results show that backreaction of the superradiant instability causes the black hole to lose charge and mass to the scalar field, with the final state described by a "hairy" black hole. I discuss implications of this work on the original problem of the rotating black hole superradiant instability, as well as applications to asymptotically flat black holes in astrophysics.