Black holes as gravitational mirrors

TL;DR

This paper investigates the theoretical possibility of using black holes as gravitational mirrors to observe past solar system objects through retrolensing, focusing on photon trajectories around Reissner-Nordström black holes and proposing new observational scenarios.

Contribution

It introduces the novel idea of studying returning photons of planets in retrolensing geometry, expanding the scope beyond stars and analyzing photon trajectories in Reissner-Nordström spacetime.

Findings

Photons can return to their emission point depending on emission angle and source position.

Retrolensing geometry with black holes can potentially observe past solar system objects.

First proposal to study planetary retrolensing photons instead of stellar ones.

Abstract

Retrolensing is a gravitational lensing effect in which light emitted by a background source is deflected by a black hole and redirected toward the observer after undergoing nearly complete loops around the black hole. In this context, we explore the possibility of seeing objects of the solar system in past eras through telescope observations by using black holes as a gravitational mirror. We consider the motion of the light around Reissner-Nordstr\"om space-time and discuss the properties of the trajectories of boomerang photons. It was shown that, depending on the angle of emission and the position of the source, the photons could return to the emission point. Afterward, we explore the possibility of considering the returning photons in retrolensing geometry where the observer is between the source and the lens in which two classes of black holes are explored: The supermassive Sgr A* black hole at the galactic center and a nearby stellar black hole. For the first time in the literature, we propose the study of the returning photons of planets instead of stars in retrolensing geometry.