Effect of electric interaction on the deflection and gravitational lensing in the strong field limit

TL;DR

This paper investigates how electric charge influences the deflection and gravitational lensing of signals in strong gravitational fields, revealing that electric interactions significantly alter lensing characteristics and black hole shadow sizes.

Contribution

It introduces a perturbative method for analyzing charged signal deflection in strong fields, incorporating electric effects into gravitational lensing calculations.

Findings

Electric repulsion decreases the critical impact parameter

Electric attraction increases the black hole shadow size

Electric interactions affect image positions, magnifications, and time delays

Abstract

The deflection angle $\Delta\phi$ of charged signals in general charged spacetime in the strong field limit is analyzed in this work using a perturbative method generalized from the neutral signal case. The solved $\Delta\phi$ naturally contains the finite distance effect and takes a quasi-power series form with a logarithmic divergence at the leading order. The coefficients of the series contain both the gravitational and electric contributions. Using the Reissner-Nordstr\"{o}m spacetime as an example, we found that an electric repulsion (or attraction) tends to decrease (or increase) the critical impact parameter $b_c$. If the repulsion is strong enough, then $b_c$ can shrink to zero and the critical particle sphere $r_{0c}$ will disappear. These results are applied to the gravitational lensing of charge signal, from which we solved the image positions, their magnifications and time delays. It is found that in general, the electric repulsion (or attraction) will decrease (or increase) the image apparent angles, the black hole shadow size as well as their magnifications but increase (or decrease) the time delay.