Adaptive ray tracing, image diagnostics, and photon ring signatures of rotating dark-matter-dressed black holes

TL;DR

This study explores how dark matter environments influence the optical appearance of rotating black holes using ray tracing, revealing observable deviations that could impact black hole imaging and analysis.

Contribution

It introduces a flexible framework comparing dark matter-dressed black holes with Kerr spacetime, highlighting observable effects of dark matter on black hole images.

Findings

Einasto-supported geometry closely resembles Kerr

Cored-NFW dark matter causes significant image redistribution

Dark matter effects can mimic or alter spin and inclination signatures

Abstract

We study the optical appearance of rotating black holes embedded in dark matter environments using a phenomenological ray tracing framework. Rather than focusing on a single geometry, we compare two effective rotating backgrounds obtained from static dark matter sourced seed metrics: a regular Einasto-type black hole and a cored-NFW black hole. Kerr is used as the reference spacetime. We construct observer-screen images by numerical backward ray tracing and analyse the horizon structure, shadow boundary, lensing bands, transfer maps, and synthetic intensity distributions produced by a common semi-analytic accretion prescription. We also introduce simple image-level diagnostics, an angular-size confrontation with M87* and Sgr A*, and simplified visibility-amplitude diagnostics. These additions are not intended as an EHT fit, but as a controlled way to identify which observables are most affected by the dark matter dressing. For the representative parameters considered here, the Einasto-supported geometry remains very close to Kerr, while the cored-NFW case produces a stronger redistribution of the image, with larger centroid displacement, stronger brightness asymmetry, an outward shift of the characteristic bright-ring scale, and a visible change in the normalized visibility amplitude. The results indicate that rotating dark-matter-dressed backgrounds can produce systematic image-domain and Fourier-domain deviations that are partially degenerate with spin, inclination, and emission modelling. The framework is lightweight and extensible, and provides a first step toward future GRRT and GRMHD studies of rotating black holes in dark matter environments.