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The geometry of photon surfaces
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The photon sphere concept in Schwarzschild space-time is generalized to a definition of a photon surface in an arbitrary space-time. A photon sphere is then defined as an SO(3)xR-invariant photon surface in a static spherically symmetric space-time. It is proved, subject to an energy condition, that a black hole in any such space-time must be surrounded by a photon sphere. Conversely, subject to an energy condition, any photon sphere must surround a black hole, a naked singularity or more than a certain amount of matter. A second order evolution equation is obtained for the area of an SO(3)-invariant photon surface in a general non-static spherically symmetric space-time. Many examples are provided.
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Cited by 7 Pith papers
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A Complete Invariant Analysis of the Kerr Spacetime and its Photon Region
An invariant function is derived whose zeros identify spherical photon orbits in Kerr spacetime, parameterized by an inclination angle, enabling invariant characterization of the photon region and constants of motion.
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Reference-renormalized curvature-primitive Gauss-Bonnet formalism for finite-distance weak gravitational lensing in static spherical spacetimes
A reference-renormalized curvature-primitive Gauss-Bonnet formalism computes finite-distance weak deflection angles in static spherical spacetimes without invoking photon spheres.
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Photon Surfaces in Higher-Curvature Gravity: Implications for Quasinormal Modes and Gravitational Lensing
Higher-curvature EFT terms modify the photon sphere radius, critical impact parameter, and strong deflection coefficients, providing sensitive probes for constraints on quantum gravity effects via lensing and QNM spectra.
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Effective null geodesics and black hole images in Kruglov nonlinear electrodynamics
In Kruglov's Born-Infeld-type nonlinear electrodynamics, the effective photon geometry around a charged black hole produces q-dependent shifts in light deflection, shadow radius, and accretion disk images, including s...
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In Kruglov nonlinear electrodynamics, small positive values of the parameter q produce stable photon orbits outside the event horizon and modify black hole shadows and relativistic images even when the spacetime metri...
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Scalar-Electromagnetic Couplings as Source of Deformed Black Hole: From Shadows to Thermodynamic Topology
A scalar-NED coupled black hole metric is reconstructed from an effective geometry, yielding EHT bounds on magnetic charge, Hawking-Page transition, and topological equivalence to the Reissner-Nordström solution.
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Photon Sphere and Shadow of a Perturbative Black Hole in $f(R,\mathcal{G})$ Gravity
Perturbative higher-curvature corrections in f(R,G) gravity shift the photon-sphere radius and black-hole shadow size away from Schwarzschild values, with the Gauss-Bonnet sector contributing more than mixed terms.
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