Optical Aspect of Cosmological Black Holes in Einstein-Maxwell-Dilaton Theory

Abstract

Motivated by string theory scenarios, we study the optical aspect of AdS black holes in Einstein-Maxwell-dilaton theory. Concretely, we investigate and examine the shadows and the deflection angle of light rays by such cosmological black holes. Concerning the shadows, we first deal with the non-rotating solutions. In particular, we obtain perfect circular shadows where their sizes are controlled by the involved parameter including the charge and the cosmological constant. Combining the Newman-Janis formalism and the Hamilton-Jacobi algorithm, we approach the rotating black hole solutions using real curves. Among others, we observe that the size and shape shadows depend on the rotating parameter and the remaining ones. To make contact with Event Horizon Telescope observational data, we show that certain constrains should be imposed on such parameters. Then, we study the behaviors of the light rays near to such cosmological black holes by computing the deflection angle in terms of Einstein-Maxwell-dilaton theory parameters. Specifically, we reveal that the effect of the cosmological constant on the deflection angle changes as the coupling between the black hole parameters is adjusted. When the rotation parameter is introduced, we observe this effect becomes similar to that of the cosmological constant in ordinary AdS black holes.