Strong field gravitational lensing of particles by a black-bounce-Schwarzschild black hole

TL;DR

This paper investigates the strong gravitational lensing of particles by a black-bounce-Schwarzschild black hole, deriving observable effects and analyzing the impact of particle velocity deviations on lensing signals, with potential astronomical implications.

Contribution

It introduces a detailed analysis of particle lensing in black-bounce-Schwarzschild spacetime, including velocity effects on lensing observables, extending previous photon-focused studies.

Findings

Derived the particle sphere and unstable orbit equations.

Calculated strong deflection lensing observables for relativistic particles.

Analyzed velocity effects on lensing signals for Sgr A*.

Abstract

The gravitational lensing of relativistic and nonrelativistic neutral massive particles in the black-bounce-Schwarzschild black hole spacetime is investigated in the strong deflection limit. Beginning with the explicit equations of motion of a massive particle in the regular spacetime, we achieve the equation of the particle sphere and thus the radius of the unstable timelike circular orbit. It is interesting to find that the particle sphere equation can reduce to the well-known photon sphere equation, when the particle's initial velocity is equal to the speed of light. We adopt the strong field limit approach to calculate the black-bounce-Schwarzschild deflection angle of the particle subsequently, and obtain the strong-deflection lensing observables of the relativistic images of a pointlike particle source. The observables mainly include the apparent angular particle sphere radius, the angular separation between the outermost relativistic image and the other ones which are packed together, and the ratio between the particle-flux magnification of the outermost image and that of the packed ones (or equivalently, their resulted magnitudelike difference). The velocity effects induced by the deviation of the initial velocity of the particle from light speed on the corresponding strong-field lensing observables of the images of a pointlike light source in the regular geometry, along with these on the strong deflection limit coefficients and the critical impact parameter of the lightlike case, are then formulated. Serving as an application of the results, we finally concentrate on evaluating the astronomical detectability of the velocity effects on the lensing observables and analyzing their dependence on the parameters, by modeling the Galactic supermassive black hole (i.e., Sgr A$^{\ast}$) as the lens.