Perturbative approach to the quasinormal modes of dirty black holes

Using a recently developed perturbation theory for quasinormal modes (QNM's), we evaluate the shifts in the real and imaginary parts of the QNM frequencies due to a quasistatic perturbation of the black hole spacetime. We show the perturbed QNM spectrum of a black hole can have interesting features using a simple model based on the scalar wave equation.