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Horizon Instability of the Extremal BTZ Black Hole
Samuel E. Gralla, Arun Ravishankar, Peter Zimmerman
We study real-time propagation of a massive scalar field on the extremal BTZ black hole spacetime, focusing on the Aretakis instability of the event horizon. We obtain a simple tim…
The Null Geodesics of the Kerr Exterior
Samuel E. Gralla, Alexandru Lupsasca
The null geodesic equation in the Kerr spacetime can be expressed as a set of integral equations involving certain potentials. We classify the roots of these potentials and express…
Lensing by Kerr Black Holes
Samuel E. Gralla, Alexandru Lupsasca
Interpreting horizon-scale observations of astrophysical black holes demands a general understanding of null geodesics in the Kerr spacetime. These may be divided into two classes:…
Black Hole Shadows, Photon Rings, and Lensing Rings
Samuel E. Gralla, Daniel E. Holz, Robert M. Wald
The presence of a bright "photon ring" surrounding a dark "black hole shadow" has been discussed as an important feature of the observational appearance of emission originating nea…
X-ray Lightcurves from Realistic Polar Cap Models: Inclined Pulsar Magnetospheres and Multipole Fields
Will Lockhart, Samuel E. Gralla, Feryal Özel +1
Thermal X-ray emission from rotation-powered pulsars is believed to originate from localized "hotspots" on the stellar surface occurring where large-scale currents from the magneto…