QED Effects on Kerr Black Hole Shadows immersed in uniform magnetic fields

TL;DR

This paper investigates how quantum electrodynamics (QED) effects and uniform magnetic fields influence the shadows of Kerr black holes, revealing distinctive photon 'hairs' that could serve as magnetic field signatures.

Contribution

It introduces a dimensionless parameter to quantify magnetic field strength and analyzes their impact on black hole shadows, including the emergence of photon hairs.

Findings

Photon hairs appear near the shadow's edge in magnetic fields.

Photon hairs become more prominent with stronger magnetic fields and higher black hole spins.

Magnetic fields cause measurable deformation of the black hole shadows.

Abstract

In this work, taking the QED effect into account, we investigate the shadows of the Kerr black holes immersed in uniform magnetic fields through the numerical backward ray-tracing method. We introduce a dimensionless parameter $\Lambda$ to characterize the strength of magnetic fields and studied the influence of magnetic fields on the Kerr black hole shadows for various spins of the black holes and inclination angles of the observers. In particular, we find that the photon "hairs" appear near the left edge of the shadow in the presence of magnetic fields. The photon hairs may be served as a signature of the magnetic fields. We notice that the photon hairs become more evident when the strength of magnetic fields or the spin of the black hole becomes larger. In addition, we study the deformation of the shadows by bringing in quantitative parameters that can describe the position and shape of the shadow edge.