Constrained Deflection Angle and Shadows of Rotating Black Holes in Einstein-Maxwell-scalar Theory

TL;DR

This paper explores how the shadow and light deflection angles of rotating black holes in Einstein-Maxwell-scalar theory are affected by a coupling parameter, aligning theoretical predictions with recent observational data.

Contribution

It introduces constraints on the stringy coupling parameter in Einstein-Maxwell-scalar gravity and analyzes their effects on black hole shadows and light deflection angles.

Findings

Shadow geometries match observational data under certain parameter constraints.

Deflection angle can be decomposed into contributions from the coupling parameter.

Optical properties depend significantly on the coupling parameter $eta$.

Abstract

Motivated by recent Event Horizon Telescope findings, we investigate constrained optics of rotating black holes in Einstein-Maxwell-scalar gravity theory. Precisely, we mainly study the parameter effects on two relevant optical concepts being the shadow and deflection angle. Using the Hamilton-Jacobi algorithm, we find certain shadow geometries being corroborated by observational data once appropriate constraints on a stringy coupling parameter $\beta$ are imposed. For such constrained regions of the black hole moduli space, we compute the deflection angle of light rays near to such black holes. Concretely, we show that this optical quantity can be split into two contributions describing the absence and the presence of the coupling parameter $\beta$. Then, we discuss and analyse such an optical quantity in terms of $\beta$ contributions.