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Particle motion near high-spin black holes

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arxiv 1905.11406 v2 pith:QUBBDZ5J submitted 2019-05-27 hep-th gr-qc

classification hep-thgr-qc
keywords blackkerrnhekequationgeodesichigh-spinholeholes
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General relativity predicts that the Kerr black hole develops qualitatively new and surprising features in the limit of maximal spin. Most strikingly, the region of spacetime near the event horizon stretches into an infinitely long throat and displays an emergent conformal symmetry. Understanding dynamics in this NHEK (Near-Horizon Extreme Kerr) geometry is necessary for connecting theory to upcoming astronomical observations of high-spin black holes. We review essential properties of NHEK and its relationship to the rapidly rotating Kerr black hole. We then completely solve the geodesic equation in the NHEK region and describe how the resulting trajectories transform under the action of its enhanced symmetries. In the process, we derive explicit expressions for the angular integrals appearing in the Kerr geodesic equation and obtain a useful formula, valid at arbitrary spin, for a particle's polar angle in terms of its radial motion. These results will aid in the analytic computation of astrophysical observables relevant to ongoing and future experiments.

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Cited by 4 Pith papers

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    Merger remnant mass and spin are claimed to maximize the average Lyapunov exponent of the photon shell of an effective Kerr black hole, matching numerical relativity fits within a few percent for q ≲ 20.

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  4. Influence of Observer Inclination and Spacetime Structure on Photon Ring Observables

    gr-qc 2024-11 conditional novelty 6.0 of 10

    For Johannsen-Psaltis spacetimes, the polar photon-ring time delay depends only on spin and shadow size, while the azimuthal shift probes the metric ratio F/N, enabling future spin and frame-dragging tests.

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