Optical appearance of the Konoplya-Zhidenko rotating non-Kerr black hole surrounded by a thin accretion disk

TL;DR

This paper investigates the optical appearance of a Konoplya-Zhidenko rotating non-Kerr black hole with a thin accretion disk, analyzing how different parameters and viewing angles affect the observed shadow, image structure, and redshift distribution.

Contribution

The study provides the first detailed simulation of the black hole shadow and accretion disk images for a Konoplya-Zhidenko non-Kerr black hole, considering various observational angles and disk motions.

Findings

Inner shadow appears as a dark region with a photon ring.

Image structure varies from superimposed to distinct as viewing angle increases.

Redshift and blueshift are observable at higher inclination angles.

Abstract

In this study, we analyze the observational images of a Konoplya-Zhidenko rotating non-Kerr black hole, wherein a thin accretion disk, serving as the sole background light source, is situated on the equatorial plane of the black hole. The inner boundary of the thin accretion disk extends to the event horizon, and the accretion material in the disk exhibits two different motion behaviors, that is, it moves along the critical plunging orbit inside the innermost stable circular orbit (ISCO) and follows the Keplerian orbit outside the ISCO. The shadow image is captured on the imaging plane of a zero angular momentum observer utilizing advanced fisheye camera ray-tracing techniques. The results demonstrate that an image consistently reveals a dark region encircled by a narrow photon ring, which is called the inner shadow. At low observation inclination angles, the observation intensity is highly concentrated, with the lensed image of accretion disk being superimposed on the direct image. As observation inclination angle increases, the direct and lensed images gradually separate, becoming distinctly distinguishable and forming a hat-like structure. Furthermore, variations in the parameter space and observation angle will influence pertinent image characteristics, including image symmetry, the range or deformation degree of the inner shadow. We further examined the distinctive characteristics of images observed in both prograde and retrograde accretion disk scenarios. Subsequently, we also examined the redshift distribution on the disk. The findings indicate that while variations in relevant parameters do influence the redshift distribution, the primary factor is the change in observational inclination. The observer can detect both redshift and blueshift phenomena on the screen when viewed at a higher observation angle.