Friday, April 5, 2013

1304.1160 (Paolo Pani et al.)

Gravito-Electromagnetic Perturbations of Kerr-Newman Black Holes:
Stability and Isospectrality in the Slow-Rotation Limit

Paolo Pani, Emanuele Berti, Leonardo Gualtieri
The most general stationary black-hole solution of Einstein-Maxwell theory in vacuum is the Kerr-Newman metric, specified by three parameters: mass M, spin J and charge Q. Within classical general relativity, the most important and challenging open problem in black-hole perturbation theory is the study of gravitational and electromagnetic fields in the Kerr-Newman geometry, because of the indissoluble coupling of the perturbation functions. Here we circumvent this long-standing problem by working in the slow-rotation limit. We compute the quasinormal modes up to linear order in J for any value of Q and provide the first, fully-consistent stability analysis of the Kerr-Newman metric. For scalar perturbations the quasinormal modes can be computed exactly, and we demonstrate that the method is accurate within 3% for spins J/Jmax<~0.5, where Jmax is the maximum allowed spin for any value of Q. Quite remarkably, we find numerical evidence that the axial and polar sectors of the gravito-electromagnetic perturbations are isospectral to linear order in the spin. If this isospectrality holds at any order in the spin, it may have important implications in the context of the gauge/gravity duality.
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