Shadow and Optical Imaging in Einstein-Maxwell-Dilaton Black Hole

TL;DR

This study analyzes photon trajectories and shadow features of Einstein-Maxwell-dilaton black holes, using observational data to constrain magnetic charge and exploring how accretion models influence shadow appearance and brightness.

Contribution

It provides a detailed analysis of black hole shadows in Einstein-Maxwell-dilaton theory, linking shadow properties to magnetic charge and accretion models, and constrains magnetic charge using Event Horizon Telescope data.

Findings

Shadow radius remains unchanged across accretion models.

Lensing and photon ring widths increase with magnetic charge q.

Brightness is mainly from direct emission, with secondary contributions from lensing rings.

Abstract

This paper investigates photon motion in black hole of Einstein-Maxwell-dilaton theory, exploring black hole shadows and observational characteristics under various accretion models. We first give the relation of the event horizon, photon sphere, and critical impact parameter in terms of the magnetic charge $q$. We then use the Event Horizon Telescope data to constrain $q$. For the two spherical accretion models, the infalling scenario yields a darker shadow due to the Doppler effect. However, the shadow radius remains unchanged for different models. In the case of an optically thin, geometrically thin disk accretion model, the observed brightness is predominantly determined by direct emission. The lensing ring provides a secondary contribution to the intensity, whereas the photon ring's emission is negligible. The widths of the lensing and photon rings exhibit a positive correlation with the magnetic charge $q$. Additionally, within the disk model framework, the black hole shadow radius is found to depend on the specific emission model.