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On the Size of Rotating Black Holes

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arxiv 1911.12368 v1 pith:VW4M4MZW submitted 2019-11-27 gr-qc hep-th

On the Size of Rotating Black Holes

classification gr-qc hep-th
keywords blackholesrotatingholeinequalitiessequenceshadowsize
verification ladder T0 review T1 audit T2 compute T3 formal T4 reserved
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Recently a sequence of inequalities relating the black hole horizon, photon sphere, shadow were proposed for spherically symmetric and static black holes, providing the upper bound for given mass. In this paper, we extend the discussion to include rotating black holes. When viewed from the north pole direction, the shadow remains a round disk, but the image is skewed when viewed from the equatorial plane. After properly implementing the ``size'' parameters for the rotating black holes, we verify that the sequence of inequalities remain valid for a variety of solutions, including Kerr, Kerr-Newman, Kerr-Sen and Kerr-Cveti\v c-Youm black holes. The upshot is that rotation makes both the actual and apparent sizes of a black hole smaller.

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Cited by 3 Pith papers

Reviewed papers in the Pith corpus that reference this work. Sorted by Pith novelty score.

  1. Bounds on the radius of outermost photon sphere and black hole shadow in $n$-dimensional Einstein gravity

    gr-qc 2026-06 unverdicted novelty 7.0

    Proves model-independent lower bound r_sh ≥ ((n-1)/2)^{1/(n-3)} sqrt((n-1)/(n-3)) r_H under WEC and upper bound r_sh ≤ sqrt((n-1)/(n-3)) [(n-1)M]^{1/(n-3)} under WEC+SEC+decay for nD black holes.

  2. The existence and upper bound for stable photon spheres in static spherically symmetric black holes

    gr-qc 2025-08 conditional novelty 6.0

    For static spherical black holes with monotone m(r)/r^3, every stable photon sphere obeys r < 6M.

  3. Bounds on the radius of outermost photon sphere and black hole shadow in $n$-dimensional Einstein gravity

    gr-qc 2026-06 accept novelty 5.0

    For n-dimensional Einstein-gravity black holes with matter satisfying the weak and strong energy conditions, the shadow radius is bounded below by a function of the horizon radius and above by a function of the ADM ma...