Puffy accretion disks: sub-Eddington, optically thick, and stable

TL;DR

This paper introduces a new class of black hole accretion disk solutions that are sub-Eddington, optically thick, and stable, combining features of thin, slim, and thick disks based on advanced simulations.

Contribution

The study presents novel, realistic accretion disk solutions derived from 3D radiative MHD simulations, differing from traditional models and applicable to non-spinning black holes.

Findings

Disk appears thin by density scale-height but has a geometrically thick, advective, turbulent region.

Magnetic support makes the disk thermally stable despite radiation pressure dominance.

A significant portion of radiation is captured by the black hole, reducing luminosity.

Abstract

We report on a new class of solutions of black hole accretion disks that we have found through three-dimensional, global, radiative magnetohydrodynamic simulations in general relativity. It combines features of the canonical thin, slim and thick disk models but differs in crucial respects from each of them. We expect these new solutions to provide a more realistic description of black hole disks than the slim disk model. We are presenting a disk solution for a non-spinning black hole at a sub-Eddington mass accretion rate, $\dot M=0.6\,\dot M_{\rm Edd}$. By the density scale-height measure the disk appears to be thin, having a high density core near the equatorial plane of height $h_{\rho} \sim 0.1 \,r$, but most of the inflow occurs through a highly advective, turbulent, optically thick, Keplerian region that sandwiches the core and has a substantial geometrical thickness comparable to the radius, $H \sim r$. The accreting fluid is supported above the midplane in large part by the magnetic field, with the gas and radiation to magnetic pressure ratio $\beta \sim 1$, this makes the disk thermally stable, even though the radiation pressure strongly dominates over gas pressure. A significant part of the radiation emerging from the disk is captured by the black hole, so the disk is less luminous than a thin disk would be at the same accretion rate.