Polarized Radiative Transfer of Kerr-Newman Black Hole

TL;DR

This paper develops a numerical framework to analyze how black hole charge influences photon trajectories and polarization patterns, revealing potential observational signatures of black hole charge.

Contribution

It extends the Walker-Penrose method by constructing an ODE-based numerical framework for polarization transport in arbitrary spacetimes, enabling analysis without symmetry constraints.

Findings

Black hole charge significantly alters photon trajectories and polarization patterns.

Charge increases compressions and distortions in EVPA structures on photon-ring scales.

Localized rotations and asymmetries in polarization may diagnose black hole charge.

Abstract

In this analysis, we investigate the polarization radiation imaging of Kerr-Newman black holes, with a particular focus on the impact of black hole charge on photon propagation and polarization characteristics. By extending the traditional Walker-Penrose method, which is limited by its reliance on specific symmetric structures and Killing tensors, we overcome these limitations by constructing an ordinary differential equations (ODEs) numerical framework that combines the photon orbit equation with the polarization parallel transport equation. This allows for the self-consistent evolution of photon trajectories and polarization states in any spacetime backgrounds without relying on specific symmetries. Using this framework, we analyze the effects of black hole spin and charge on the polarization characteristics of radiation from both prograde and retrograde accretion disks. Our results show that black hole charge can significantly modify photon trajectories and polarization patterns: increasing charge compresses and distorts the EVPA structure on photon-ring scales, inducing localized rotations and asymmetries that may provide a potential diagnostic of a nonzero black hole charge.