Impact of Perfect Fluid Dark Matter on the Appearance of Rotating Black Hole

TL;DR

This paper investigates how perfect fluid dark matter influences the observable features of rotating black holes, using analytical and numerical methods to compare simulations with Event Horizon Telescope data, revealing potential dark matter signatures.

Contribution

It introduces a combined analytical and numerical framework to study the effects of perfect fluid dark matter on black hole images and constrains dark matter parameters using EHT observations.

Findings

PFDM improves the match between simulated and observed black hole images.

Dark matter leaves observable imprints on photon rings and brightness distributions.

Constraints on PFDM parameters are derived from EHT data.

Abstract

Understanding how dark matter affects the immediate environment of black holes (BHs) is crucial for interpreting horizon-scale observations. We study rotating BHs surrounded by perfect fluid dark matter (PFDM), exploring their observable features through both analytical and numerical approaches. Using the existence criterion of the innermost stable circular orbit (ISCO), we first derive joint constraints on the PFDM intensity parameter~k and the spin parameter~a. Within the resulting physically allowed parameter regime, we perform high-resolution, general-relativistic ray-tracing simulations of thin accretion disks at 87~GHz and 230~GHz, capturing the detailed brightness morphology and photon ring structure shaped by PFDM. By incorporating angular diameter measurements of M87^{*} and Sgr~A^{*} from the Event Horizon Telescope (EHT), we further narrow down the viable parameter space and directly compare synthetic images with EHT observations of M87^{*}. We find that the inclusion of PFDM improves the agreement with the observed compact shadow and asymmetric brightness distribution, suggesting that dark matter may leave observable imprints on horizon-scale images. Our results position PFDM as a physically motivated extension to the Kerr geometry and highlight a promising astrophysical pathway for probing dark matter near BHs with current and future VLBI campaigns.