Analyzing the Influence of Geometrical Deformation on Photon Sphere and Shadow Radius: A New Analytical Approach -Stationary, and Axisymmetric Spacetime

TL;DR

This paper investigates how geometrical deformations affect black hole shadow sizes and shapes using an analytical approach, highlighting complexities beyond spherical symmetry and the influence of accretion discs.

Contribution

It introduces a new analytical method applying gravitational decoupling to axisymmetric spacetimes to analyze black hole shadows under deformations.

Findings

Shadow size complexity increases with deformation

Accretion disc influence on shadow shape is significant

Method compares well with known models

Abstract

Black hole shadows and photon spheres offer valuable tools for investigating black hole properties. Recent observations by the Event Horizon Telescope Collaboration have confirmed the existence of rotating black holes. Black hole parameters influence the observed shadow size. This paper explores the impact of geometrical deformations on black hole shadow size using gravitational decoupling applied to axially-symmetric spacetime. We find the results are more complex than the spherically-symmetric case. We compare shadows in well-known models with those of an Kerr black hole. Our approach suggests that the influence of an accretion disc on the observed shadow shape can be accurately described despite negligible impact on the black hole geometry itself.