Optical Signatures of a Schwarzschild Black Hole in a Dehnen-Type Dark Matter Halo

TL;DR

This study investigates how a Dehnen-type dark matter halo influences optical phenomena like gravitational lensing and black hole shadows around a Schwarzschild black hole, revealing the combined effects of dark matter and plasma on observable signals.

Contribution

The paper provides analytical and numerical analysis of lensing and shadow features considering both dark matter halos and plasma effects, extending previous models to more realistic astrophysical environments.

Findings

Dark matter halo parameters significantly affect black hole shadow size and shape.

Plasma presence alters deflection angles and magnification, impacting observational signatures.

Analytical expressions for deflection angles in plasma environments are derived.

Abstract

In this paper, the optical effects that occur near a Schwarzschild-like black hole (BH) with a Dehnen-type $(1,4,2)$ dark matter (DM) halo are explored. We first derive the photon sphere radius and obtain an analytical expression for the deflection angle in the weak-field regime by applying the Gauss-Bonnet theorem (GBT). For the strong-field regime, we perform ray-tracing calculations to examine the behavior of light trajectories and determine the corresponding number of orbits. We further compute the BH shadow and gravitational lensing in a plasma medium and provide constraints arising from the DM halo parameters. We also extend our analysis to weak gravitational lensing within plasma environments, considering both uniform and singular isothermal sphere (SIS) distributions. We find the analytical expressions for the deflection angle in the presence of plasma and examine the resulting effects on image magnification. The overall results highlight how DM halo properties and plasma characteristics jointly alter observable lensing signatures.