Retrolensing by two photon spheres of a black-bounce spacetime

TL;DR

This paper studies how light bends and reflects around a novel black-bounce spacetime with two photon spheres, revealing dominant retrolensing effects from the outer photon sphere in such exotic geometries.

Contribution

It introduces the analysis of retrolensing phenomena in a new black-bounce spacetime with two photon spheres, including wormhole configurations, and identifies the dominant retrolensing effects.

Findings

Light rays reflected by the outer photon sphere dominate retrolensing light curves.

Retrolensing signatures depend on the photon sphere structure of the spacetime.

The study extends understanding of gravitational lensing in exotic compact objects.

Abstract

We investigate retrolensing by two photon spheres in a novel black-bounce spacetime suggested by Lobo et al. which can correspond to a Schwarzschild black hole, a regular black hole, and a traversable wormhole including an Ellis-Bronnikov wormhole. In a case, the wormhole has a throat which acts as a photon sphere and it has another photon sphere outside of the throat. With the sun as a light source, an observer, and the wormhole are lined up in this order, sunlight reflected slightly outside of the throat and barely outside and inside of the outer photon sphere can reach the observer. We show that the light rays reflected by the outer photon sphere are dominant in retrolensing light curves in the case.