Shadow of a Kerr-Sen dilaton-axion Black Hole

TL;DR

This paper studies the shadow of a Kerr-Sen dilaton-axion black hole, examining how charge, spin, and plasma influence its apparent size and shape in different observational conditions.

Contribution

It provides a detailed analysis of black hole shadows considering both vacuum and plasma environments, highlighting the effects of charge, spin, and plasma parameters.

Findings

Increasing electric charge decreases shadow size.

Higher spin parameter reduces shadow size.

Presence of plasma and its refraction index significantly affect shadow appearance.

Abstract

We analyze the shadow of charged stationary axially symmetric space-time (Kerr-Sen dilaton-axion black hole). This black hole is defined by a mass $M$, a spin $a$ and $r_{\alpha}=Q^{2}/M$, where $Q$ is the electric charge. Shadows are investigated in two conditions, i) for an observer at infinity in vacuum and ii) for an observer at infinity in the presence of plasma with radial power-low density. In vacuum, the shadow of this black hole depends on charge and spin parameter. We can see that, increasing electric charge, $Q$ decreases the size of shadow. Also, increasing spin parameter $a$ decreases the size of shadow. However, in existence of plasma, parameter of plasma like refraction index, $n$, playing an important role on shadows. In fact, decreasing refraction index decreases the size of shadow.