On null geodesics and shadow of hairy black holes in Einstein-Maxwell-dilaton gravity

TL;DR

This paper analyzes null geodesics and black hole shadows in Einstein-Maxwell-dilaton gravity, revealing how charge and dilaton coupling influence photon orbits, shadow size, and light deflection around charged dilaton black holes.

Contribution

It provides a detailed study of null geodesics and shadow properties of charged dilaton black holes, comparing results with other black hole solutions and exploring effects of model parameters.

Findings

Photon sphere radius depends on charge and dilaton coupling.

Dilaton coupling alters the size of the black hole shadow.

Light deflection is affected by the black hole's charge and dilaton parameters.

Abstract

The time-like and null-like geodesics around compact objects are some of the best tools to classify and understand the structure of a space-time. In this paper, we study the null geodesics around charged static dilaton black holes in Einstein-Maxwell-dilaton gravity. The physical parameters for non-radial geodesics including the effective potential, effective force, radius of the photon sphere and impact parameter are obtained and effects of the charge parameter and dilaton coupling constant on these quantities are studied. Possible photon motions for different values of the impact parameter are analyzed and unstable circular orbits and unbounded orbits are plotted. These results are compared to that of the Schwarzschild, Reissner-Nordstrom and Gibbons-Maeda-Garfinkle-Horowitz-Strominger (GMGHS) black holes. Also, we study the shadow cast by a dilaton black hole and investigate how the dilaton coupling affects the size of the black hole shadow. Finally, as an application of null geodesics, we calculate the deflection of light and investigate the effects of the model parameters on the bending angle.