Gravitational perturbations from NHEK to Kerr

Understand

We revisit the spectrum of linear axisymmetric gravitational perturbations of the (near-)extreme Kerr black hole.

• Our aim is to characterise those perturbations that are responsible for the deviations away from extremality, and to contrast them with the linearized perturbations treated in the Newman-Penrose formalism.
• For the near horizon region of the (near-)extreme Kerr solution, i.e.
• the (near-)NHEK background, we provide a complete characterisation of axisymmetric modes.