In a recent 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 $T_{ \text{ BH}}$.
Categories: gr-qc astro-ph.HE hep-th