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Universal bounds on the size of a black hole

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arxiv 2001.00027 v3 pith:N77U6X7C submitted 2019-12-31 gr-qc hep-th

Universal bounds on the size of a black hole

classification gr-qc hep-th
keywords mathrmareablackgeneralphotonstaticholeshorizon
verification ladder T0 review T1 audit T2 compute T3 formal T4 reserved
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For static black holes in Einstein gravity, if matter fields satisfy a few general conditions, we conjecture that three characteristic parameters about the spatial size of black holes, namely the outermost photon sphere area $A_{\mathrm{ph,out}}$, the corresponding shadow area $A_{\mathrm{sh,out}}$ and the horizon area $A_{\mathcal{H}}$ satisfy a series of universal inequalities $9A_{\mathcal{H}}/4\leq A_{\mathrm{ph,out}}\leq A_{\mathrm{sh,out}}/3\leq 36\pi M^2$, where $M$ is the ADM mass. We present a complete proof in the spherically symmetric case and some pieces of evidence to support it in general static cases. We also discuss the properties of the photon spheres in general static spacetimes and show that, similar to horizon, photon spheres are also conformal invariant structures of the spacetimes.

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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. Static spheres in black hole spacetimes: pairing, energy conditions, and an upper bound on the innermost radius

    gr-qc 2026-07 conditional novelty 6.0

    Static spheres around black holes come in unstable/stable pairs, need negative radial pressure, and their innermost radius obeys a new upper bound tied to strong-energy-condition violation.

  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...