Imprints of Dark Matter on the Shadow and Polarization Images of a Black Hole Illuminated by Various Thick Disks

TL;DR

This study explores how dark matter influences the visual and polarization features of black holes with thick accretion disks, revealing potential observational signatures of dark matter effects near the event horizon.

Contribution

It introduces a detailed analysis of dark matter's impact on black hole images and polarization using two thick disk models, highlighting observable effects linked to dark matter parameters.

Findings

Photon rings expand with dark matter parameter η.

Anisotropic radiation causes vertical distortions in images.

Polarization patterns vary with inclination and dark matter presence.

Abstract

Based on two distinct thick accretion flow disk models, such as a phenomenological RIAF-like model and an analytical Hou disk model, we investigate the impact of relevant parameters on the visual characteristics of the Schwarzschild black hole (BH) surrounded by perfect fluid dark matter (PFDM). We impose a general relativistic radiative transfer equation to determine the synchrotron emission from thermal electrons and generate horizon-scale images. In the RIAF-like model, we notice that the corresponding photon ring and central dark region are expanded with the aid of the PFDM parameter $\eta$, with brightness asymmetries originating at higher inclination angles and closely tied to flow dynamics and emission anisotropy. The fundamental difference between isotropic and anisotropic radiation is that anisotropy introduces vertical distortions in the higher-order images, resulting in an elliptical appearance. For the Hou disk model, the observed images produce narrower rings and dark interiors, while polarization patterns trace the brightness distribution and changes with the variations of the inclination angle and PFDM parameter $\eta$, which reflects the spacetime signature. All these results indicate that the observed intensity and polarization characteristics in the framework of thick disk models may serve as valuable probes of underlying spacetime geometry and the accretion-dynamics close to the horizon.