Schwarzschild Black Holes Immersed in Born-Infeld Magnetic Fields and Their Observational Signatures

TL;DR

This paper explores how Born-Infeld nonlinear electrodynamics modifies magnetic fields, photon orbits, and black hole shadows around Schwarzschild black holes, revealing significant effects near the horizon and observable shadow elongation.

Contribution

It introduces a numerical analysis of Born-Infeld magnetic fields around Schwarzschild black holes and demonstrates their impact on photon orbits and black hole shadow shapes.

Findings

Nonlinear effects intensify near the event horizon.

Photon orbits become prolate and stretch along the polar axis.

Black hole shadows elongate at high observer inclinations with increasing nonlinearity.

Abstract

We investigate the influence of Born-Infeld (BI) nonlinear electrodynamics on magnetic field configurations, photon orbits, and black hole shadows for Schwarzschild black holes immersed in magnetic fields. Assuming that the BI magnetic fields are asymptotically uniform and aligned with the polar axis, we solve the nonlinear magnetic field equations numerically using pseudospectral methods. Our analysis shows that nonlinear electromagnetic effects become prominent near the event horizon, particularly in the polar regions, where the magnetic field strength is significantly enhanced. This enhancement leads to closed photon orbits on the meridional plane becoming prolate, with noticeable stretching along the polar axis. Simulations of black hole images reveal that, at high observer inclinations, the shadow, which is circular in the Maxwell limit, becomes increasingly elongated along the polar direction as the nonlinear effects increase.