Polarization distribution in the image of a synchrotron emitting ring around a regular black hole

The polarized images of a synchrotron emitting ring are studied in the regular Hayward and Bardeen black hole spacetimes.These regular black holes carry a magnetic field in terms of gravity coupled to nonlinear electrodynamics.Results show that the main features of the polarization images of the emitting rings are similar in these two regular black hole spacetimes.As the magnetic charge parameter increases,the polarization intensity and the electric vector position angle in the image plane increase in Hayward and Bardeen black hole spacetimes.Moreover,the polarization intensity and electric vector position angle in the image of the emitting ring in the Hayward black hole spacetime are closer to those in the Schwarzschild case.The effects of the magnetic charge parameter on the Strokes Q-U loops are also slightly smaller in the Hayward black hole spacetime.This information stored in the polarization images around Hayward and Bardeen black holes could help understand regular black holes and the gravity coupled to nonlinear electrodynamics.

Onset of chaotic gravitational lensing in non-Kerr rotating black holes with quadrupole mass moment

In the electromagnetic channel,chaotic gravitational lensing is a peculiar phenomenon in strong gravita-tional lensing.In this study,we analyze the properties and emergence of chaotic gravitational lensing in the Manko-Novikov black hole spacetime.Aiming to better understand the underlying physics,we elaborate on the boundaries of the accessible region through analyses of the contours of the effective potentials.The latter is associated with the two roots of a quadratic equation.In particular,we explore its interplay with an ergoregion,which leads to specific features of the effective potentials,such as the emergence of a cuspy edge and the formation of a pocket,which serve as static constraints on the geodesics.Additionally,we investigate the properties of the radial and angular accelerations at the turning points in photon trajectories.The accelerations are further examined and may provide kinematic constraints on the geodesics,as argued herein.It is concluded that the onset of the chaotic lensing is significantly related to both con-straints;as a result,an arbitrary slight deviation in the incident photon is significantly amplified during evolution through an extensive period,demonstrating the complexity in the highly nonlinear deterministic gravitational system.