Bending angle of light in equatorial plane of Kerr-Sen Black Hole

TL;DR

This paper derives a formula for the bending angle of light around a Kerr-Sen Black Hole, considering effects of charge and spin, and compares it with Kerr Black Hole results, revealing charge's influence on gravitational lensing.

Contribution

It provides a closed-form expression for light bending in Kerr-Sen Black Hole spacetime, incorporating charge and spin effects, and compares these with Kerr Black Hole predictions.

Findings

Bending angle increases with black hole charge in strong field limit.

Charge parameter affects photon orbits similarly to spin in direct orbits.

Bending angles can exceed 2π, leading to multiple relativistic images.

Abstract

We study the gravitational lensing by a Kerr-Sen Black Hole arising in heterotic string theory. A closed form expression for the bending angle of light in equatorial plane of Kerr-Sen Black Hole is derived as a function of impact parameter, spin and charge of the Black Hole. Results obtained are also compared with the corresponding cases of Kerr Black Hole in general relativity. It is observed that charge parameter behaves qualitatively similar as the spin parameter for photons travelling in direct orbits while behaves differently for photons in retrograde orbits around Black Hole. As the numerical value of the Black Hole charge increases, bending angle becomes larger in strong field limit. Further it is observed that this effect is more pronounced in case of direct orbits in comparison to the retro orbits. For both the direct and retro motion, the bending angle exceeds 2\pi, which in turn results in multiple loops and formation of relativistic images.