A short remark (with a long title) on the universality of the quasinormal spectrum of near-extremal Kerr-Newman black holes

Abstract: In a paper (arXiv:1410.0694) Zilh~ao, Cardoso, Herdeiro, Lehner, and Sperhake have studied the nonlinear stability of Kerr-Newman black holes. We show that their numerical results for the time evolutions of the spacetime deformations of near-extremal Kerr-Newman black holes are described extremely well by a {\it universal} formula for the quasinormal resonances of the black holes. This formula is expressed in terms of the black-hole physical parameters: the horizon angular velocity $\Omega_{\text{H}}$ and the Bekenstein-Hawking temperature $T_{\text{BH}}$.