Plasma impact on black hole shadow and gravitational weak lensing for Schwarzschild-like black hole

TL;DR

This paper investigates how plasma influences the observable properties of Schwarzschild-like black holes, including their shadows and gravitational lensing, using observational data and theoretical modeling.

Contribution

It provides new insights into plasma effects on black hole shadows and lensing, constrained by EHT observational data for M87* and Sgr A*.

Findings

Plasma increases photon sphere radii and decreases shadow size with higher plasma frequency.

Uniform plasma enhances gravitational deflection angles, while non-uniform plasma reduces them.

Spacetime parameters and plasma frequencies similarly affect lensing magnification.

Abstract

This article delves into the observational properties of a Schwarzschild-like black hole (BH). Initially, the research provides a succinct examination of the spacetime geometry and the configuration of its horizon. Furthermore, we study the photon dynamics around the Schwarzschild-like BH in the presence of the plasma using the Hamiltonian formalism. It was found that the photon sphere radii increase under the influence of the plasma frequency and vice versa for the spacetime parameters. Further exploration is dedicated to understanding how the plasma affects the shadow of the BH, and we find that the radius of the BH shadow shrinks with the rise of the $\xi$ parameter and plasma frequency. We then turn to the getting constraint of the spacetime parameters and the plasma frequency by using the observational data released by the Event Horizon Telescope (EHT) collaboration for the M87* and Sgr A*. Additionally, the research scrutinises the phenomenon of gravitational weak lensing in the vicinity of a Schwarzschild-like BH, considering both uniform and non-uniform plasma scenarios. The outcomes demonstrate that the angle of deflection increases under the influence of a uniform plasma frequency, whereas the opposite is true for non-uniform plasma. In both scenarios, a rise in the spacetime parameters results in a decrease in the deflection angle. Finally, we investigate the magnification of the gravitationally lensed image. The effect of the spacetime parameters and plasma frequencies on the total magnification are same as in the deflection angles.