The Role of Inhomogeneities in the Turbulent Accretion of Black Holes

TL;DR

This study uses high-resolution GRMHD simulations to analyze how inhomogeneities like plasma bubbles affect turbulence and accretion in black hole environments, offering insights into observational features.

Contribution

It introduces a detailed simulation approach to study the impact of inhomogeneities on black hole accretion and turbulence near the event horizon.

Findings

Perturbed accretion shows steeper power spectra than unperturbed cases.

Increased correlation times indicate absorption of macro-structures at the horizon.

Larger coherent structures are present in perturbed turbulence.

Abstract

Observations of supermassive black holes by the Event Horizon Telescope reveal significant inhomogeneities, most likely related to density and magnetic field perturbations. To model these features, we conduct high-resolution 2D general-relativistic magnetohydrodynamics (GRMHD) simulations of a Fishbone-Moncrief torus around a Kerr black hole using the Black Hole Accretion Code $\texttt{BHAC}$. We compare unperturbed accretion with a case featuring plasma density bubbles with pressure balanced magnetic islands of different amplitudes. Power spectrum analysis of accretion time series, performed via the Blackman-Tukey method, shows that the perturbed case exhibits (1) steeper spectral indices compared to the unperturbed case, deviating from the characteristic $1/\omega$ noise spectrum, and (2) increased correlation times, providing evidence for absorption of macro-structures at the event horizon. Spatial auto-correlation analysis of near-horizon turbulence confirms larger energy-containing coherent structures in the perturbed case altering the accretion rate. These results provide new insights for interpreting observations of supermassive black hole environments, where near-horizon turbulence may play a key role in the accretion process.