Shadow of rotating black hole surrounded by dark matter

TL;DR

This paper explores how dark matter influences the shadow of rotating black holes, revealing that beyond a critical mass, dark matter significantly enlarges the shadow and affects its shape, with implications for astrophysical observations.

Contribution

It generalizes the Kerr black hole model to include dark matter effects using the Newman-Janis Algorithm, analyzing the impact on shadow structure and stability.

Findings

Dark matter causes significant expansion of black hole shadows above a critical mass.

The shadow remains nearly circular even for highly spinning black holes with dark matter.

Excessive dark matter mass may conflict with observational constraints, implying limits on dark matter presence near black holes.

Abstract

Dark matter (DM), a fundamental cosmic component, motivates the study of its influence on black hole (BH) shadows, especially for spinning BHs confirmed by EHT observations. This work generalizes the Schwarzschild BH surrounded by DM to an axisymmetric Kerr BH using the Newman-Janis Algorithm (NJA), investigating the resulting event horizon and ergosphere structures. Employing null geodesics, we examine the effects of DM mass ($\Delta$M) on BH shadow, including its radius, distortion, and the associated energy emission rate. Our analysis reveals that DM has a negligible effect below a critical mass, once this threshold is surpassed, all BH structures expand significantly. Furthermore, DM robustly contributes to the shadow maintaining a near circular shape, even for highly spinning BHs. This pronounced structural expansion under high DM mass may potentially exceed current observational constraints, suggesting that DM must either be absent in the immediate vicinity of the BH or its localized mass must remain below this critical value to be consistent with astrophysical observations.