Nondivergent deflection of light around a photon sphere of a compact object

Abstract

We demonstrate that the location of a stable photon sphere (PS) in a compact object is not always an edge such as the inner boundary of a black hole shadow, whereas the location of an unstable PS is known to be the shadow edge notably in the Schwarzschild black hole. If a static spherically symmetric (SSS) spacetime has the stable outermost PS, the spacetime cannot be asymptotically flat. A nondivergent deflection is caused for a photon traveling around a stable PS, though a logarithmic divergent behavior is known to appear in most of SSS compact objects with an unstable photon sphere. The reason for the nondivergence is that the closest approach of a photon is prohibited in the immediate vicinity of the stable PS when the photon is emitted from a source (or reaches a receiver) distant from a lens object. The finite gap size depends on the receiver and source distances from the lens as well as the lens parameters. The mild deflection angle of light can be approximated by an arcsine function. A class of SSS solutions in Weyl gravity exemplify the nondivergent deflection near the stable outer PS.

10 pages, 4 figures, OSPS corrected to SOPS, potential added, figure 2 replaced, accepted for PRD

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Cited by in corpus (6)

• Retrolensing by two photon spheres of a black-bounce spacetime
• General Approach on Shadow Radius and Photon Spheres in Asymptotically Flat Spacetimes and the Impact of Mass-Dependent Variations
• Gravitational lensing and accretion disk imaging of a Buchdahl dense core
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• Relation between circular photon orbits and the stability of wormholes with the thin shell of a barotropic fluid
• Strong-deflection expansion of the deflection angle near a degenerate photon sphere