Effects of hair on the image of a rotating black hole illuminated by a thin accretion disk

TL;DR

This paper explores how hair parameters in a hairy Kerr black hole affect its shadow and photon ring, suggesting future observations could constrain these parameters.

Contribution

It introduces the influence of deformation and hair parameters on black hole shadows and photon rings, providing theoretical predictions for observational constraints.

Findings

Hair and deformation parameters significantly alter the shadow size.

These parameters increase the width of the photon ring.

Shadow deformation depends on the competing effects of the parameters.

Abstract

In this paper, we investigate the shadow and optical appearance of the hairy Kerr black hole illuminated by a thin accretion disk, the materials of which outside the innermost stable circular orbit (ISCO) move on the equatorial circular orbit, while inside the ISCO they quickly plunge into the black hole. The deformation parameter $\alpha$ and hair parameter $l_o$ are found to influence the motions of accretion as well as the redshift effect of the photon, such that they significantly affect the shadow and image of the hairy Kerr black hole. Especially, these two parameters have competing effects on the size of the black hole's shadow, and significantly increase the width of photon ring. This study provides a preliminary theoretical prediction that the image of the hairy Kerr black hole, especially the photon ring structure, may be used to constrain the hair parameters with future high-precision astronomical observation.