Nonlinear black hole spectroscopy

According to general relativity, the remnant of a binary black hole merger must be a perturbed Kerr black hole. Perturbed Kerr black holes emit "ringdown" radiation which is well described by a superposition of quasinormal modes, with frequencies and damping times that depend only on the mass and spin of the remnant, but nonlinear corrections have proven to be important. I will give an overview of recent progress by our group on this "nonlinear black hole spectroscopy" program, and present some highlights of work that will be discussed in more detail by Johns Hopkins students. I will focus on three important open issues: (1) Can we identify nonlinear effects in numerical relativity simulations? (2) What are the prospects of observing these nonlinear effects? (3) Can ringdown be used to constrain modified gravity theories?