Geodesic of nonlinear electrodynamics and stable photon orbits

TL;DR

This paper investigates the geodesics of charged black holes in nonlinear electrodynamics models, revealing stable photon orbits outside the horizon and calculating deflection angles, with some models deemed unphysical.

Contribution

It analyzes photon orbits and deflection angles in various NLED black hole models, highlighting stable photon orbits and identifying unphysical models.

Findings

Photon can orbit extremal black holes in stable radii outside the horizon.

Corrections to the weak deflection angle are obtained for null scattering states.

The power-law model is ruled out as unphysical due to inconsistent deflection angle behavior.

Abstract

We study the geodesics of charged black holes in polynomial Maxwell Lagrangians, a subclass of models within the nonlinear electrodynamics (NLED). Specifically, we consider black holes in Kruglov, power-law, and Ayon-Beato-Garcia models. Our exploration on the corresponding null bound states reveals that photon can orbit the extremal black holes in stable radii outside the corresponding horizon. The reason behind this is the well-known theorem that a photon in a NLED background propagates along its own {\it effective} geometry. This nonlinearity is able to shift the local minimum of the effective potential away from its corresponding outer horizon. For the null scattering states we obtain corrections to the weak deflection angle off the black holes. We rule out the power-law model to be physical since its deflection angle does not reduce to the Schwarzschild in the limit of the vanishing charge.