University of Arizona

## Talks by Peter Zimmerman

## Gauge and effective source regularization of reconstructed metric perturbations

Peter Zimmerman
University of Arizona

Understanding extended sources is an important aspect of the second-order problem in Kerr. Metric reconstruction procedures based on the Teukolsky equation bring challenges at second order due to singularities in the radiation gauge. One approach would be to soften these singularities using an effective source derived from a puncture. I will describe how the corrector-tensor reconstruction algorithm may be applied in a puncture scheme with a spatially compact effective source.

## Near-horizon instability of rapidly rotating black holes

Peter Zimmerman
University of Arizona

Aretakis' discovery of a horizon instability of extremal black holes came as something of a surprise given earlier proofs that individual frequency modes are bounded. Is this kind of instability invisible to frequency-domain analysis? The answer is no: We show that the horizon instability can be recovered in a mode analysis as a branch point at the horizon frequency. We use the approach to generalize to nonaxisymmetric gravitational perturbations and reveal that certain Weyl scalars are unbounded in time on the horizon.

## Electromagnetic Self-force and Overcharging a Reissner-Nordstrom Black Hole

Peter Zimmerman
University of Arizona

TBA