Gravitational shadow and emission spectrum of thin accretion disks in a plasma medium

TL;DR

This paper models the appearance of thin accretion disks around black holes in plasma environments, predicting frequency-dependent shadow images to aid future multi-frequency observations by ngEHT.

Contribution

It introduces a relativistic radiative transfer model for accretion disks in plasma, including dispersion effects, to generate spectral images across frequencies.

Findings

Shadow images vary significantly with frequency.

Plasma effects influence the observed intensity maps.

Results suggest potential for extracting plasma properties from future observations.

Abstract

In anticipation of future multi-frequency observations of black hole with the Next Generation Event Horizon Telescope (ngEHT), we construct spectral images of a thin accretion disk around a spherically symmetric black hole immersed in cold, non-magnetized, pressureless plasma. The radiation from the disk is assumed to be thermal, and the surrounding plasma is entrained by its rotation. We use the general relativistic transport equation for the radiation in the plasma, accounting for both dispersion and plasma motion but neglecting absorption. Shadow images and intensity maps are computed across the full spectrum for an inverse power-law plasma density profile. The results show a strong dependence of the observed images on the radiation frequency, which looks promising for the possibility of extracting new information in future observations of the ngEHT.