Shadow bound of black holes with dark matter halo

TL;DR

This paper analyzes how dark matter halos affect black hole shadows, using EHT data to constrain halo parameters and compare with galactic bounds.

Contribution

It introduces a method to constrain dark matter halo parameters around black holes using shadow observations, providing new bounds on halo size.

Findings

Favored dark matter halo parameter region for a≥10.8M

Disfavored region for a<10.8M

Shadow bounds are much less restrictive than galactic bounds

Abstract

We investigate the shadow cast of black holes immersed in a dark matter halo. We use the M87* shadow data obtained by the EHT collaboration to constrain two parameters ($M,a$) of dark matter halo surrounding a black hole with mass $M_{\rm bh}$. For $a\ge10.8M$, we find the favored region (shadow bound), while the disfavored region is found for $a<10.8M$ when imposing the EHT results. This shadow bound is much less than the observation bound of galaxies ($a\ge 10^4 M$).