Null geodesics around a black hole with weakly coupled global monopole charge

Abstract

In this paper, we study an asymptotically flat black hole spacetime with weakly nonminimally coupled monopole charge. We analytically and numerically investigate light ray propagation around such a black hole by employing the common Lagrangian formalism. Our analysis encompasses both radial and angular geodesics, for which we present analytical solutions in terms of incomplete Lauricella hypergeometric functions. Additionally, we explore the impact of the coupling constant on geodesic motion. Based on observations from the Event Horizon Telescope, we constrain the black hole parameters, resulting in a coupling constant range of $-0.5\lesssim \alpha\lesssim 0.5$. Throughout our analysis, we simulate all possible trajectories and, where necessary, perform numerical inversion of the included integrals.