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Lower bound on the radii of light rings in traceless black-hole spacetimes

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arxiv 2311.17462 v2 pith:K3KIHIRU submitted 2023-11-29 gr-qc astro-ph.HEhep-th

classification gr-qcastro-ph.HEhep-th
keywords black-holespacetimestracelessboundcompactlightlowerphotonspheres
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abstract

Photonspheres, curved hypersurfaces on which massless particles can perform closed geodesic motions around highly compact objects, are an integral part of generic black-hole spacetimes. In the present compact paper we prove, using analytical techniques, that the innermost light rings of spherically symmetric hairy black-hole spacetimes whose external matter fields are characterized by a traceless energy-momentum tensor cannot be located arbitrarily close to the central black hole. In particular, we reveal the physically interesting fact that the non-linearly coupled Einstein-matter field equations set the lower bound $r_{\gamma}\geq {6\over5}r_{\text{H}}$ on the radii of traceless black-hole photonspheres, where $r_{\text{H}}$ is the radius of the outermost black-hole horizon.

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Cited by 3 Pith papers

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

  1. 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 of 10

    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.

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

    gr-qc 2025-08 conditional novelty 6.0 of 10

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

  3. Bounds for Lyapunov exponent of circular light orbits in black holes

    gr-qc 2024-12 conditional novelty 6.0 of 10

    For any static, spherically symmetric black hole obeying Einstein's equations and the dominant energy condition, the circular photon orbit's Lyapunov exponent is bounded by the photon-sphere surface gravity, the Unruh...

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