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

Yuan Meng; Xi-Jing Wang; Yong-Zhuang Li; Xiao-Mei Kuang

doi:10.1140/epjc/s10052-025-14346-z

2023 Impact factor 4.2

Particles and Fields

Open Access

Eur. Phys. J. C (2025) 85: 627
https://doi.org/10.1140/epjc/s10052-025-14346-z

Regular Article - Theoretical Physics

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

Yuan Meng¹, Xi-Jing Wang², Yong-Zhuang Li³ and Xiao-Mei Kuang¹^a

¹ Center for Gravitation and Cosmology, Yangzhou University, 225009, Yangzhou, China
² Department of Astronomy, School of Physics and Technology, Wuhan University, 430072, Wuhan, China
³ Research center for theoretical physics, School of Science, Jiangsu University of Science and Technology, 212100, Zhenjiang, China

^a xmeikuang@yzu.edu.cn

Received: 28 December 2024
Accepted: 22 May 2025
Published online: 7 June 2025

Abstract

In this paper, we investigate the shadow and optical appearance of the hairy Kerr black hole illuminated by a thin accretion disk. The deformation parameter $α$ $\alpha$ and hair parameter $l_{o}$ $$l_o$$ 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. In particular, $l_{o}$ $$l_o$$ suppresses the shadow size of the black hole while $α$ $\alpha$ enhances it. We then analyze the widths of the direct, lensed ring and photon ring emission regions for the thin accretion disk. It is found that the widths of the direct emission and lensed ring emission change slightly with the parameters, whereas the width of the photon ring emission increases dramatically as $l_{o}$ $$l_o$$ decreases. This feature provides more favorable conditions for observing the photon rings of black hole. Finally, we study the redshift of the direct and lensed images, showing that the maximal blueshift point is shifted by the change of the parameters. We argue that our 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.

© The Author(s) 2025

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