Published online by Cambridge University Press: 07 February 2017
As a stopgap measure until a rigorous analytic determination is made, Teukolsky and I have tested the dynamical stability of the Kerr metric under small perturbations numerically (Press and Teukolsky, 1973). We find that it is stable for all a ≤ M. We have also computed the magnitude of electromagnetic and gravitational-wave amplification in superradiant scattering, and Bardeen has independently obtained identical results (Teukolsky, 1973; Teukolsky et al., 1974). The amplification ranges up to ~2% for electromagnetism (l=m=1) and up to 140% for gravitation (l=m=2); these values are also consistent with Starobinsky's (1973) results for the value of critical frequencies.