Global Structure of Three Distinct Accretion Flows and Outflows around Black Holes through Two-Dimensional Radiation-Magnetohydrodynamic Simulations

TL;DR

This study uses advanced simulations to explore three distinct accretion flow modes around black holes, revealing how density influences disk structure, outflows, and luminosity, with implications for understanding black hole observations.

Contribution

It introduces a comprehensive simulation framework that reproduces three different accretion flow modes based on initial density, highlighting their unique structures and outflow mechanisms.

Findings

High-density flows produce thick, supercritical disks with strong outflows.

Moderate-density flows form thin disks with magnetic-driven winds.

Low-density flows result in radiatively inefficient, thick, optically thin flows.

Abstract

We present the detailed global structure of black hole accretion flows and outflows through newly performed two-dimensional radiation-magnetohydrodynamic simulations. By starting from a torus threaded with weak toroidal magnetic fields and by controlling the central density of the initial torus, rho_0, we can reproduce three distinct modes of accretion flow. In model A with the highest central density, an optically and geometrically thick supercritical accretion disk is created. The radiation force greatly exceeds the gravity above the disk surface, thereby driving a strong outflow (or jet). Because of the mild beaming, the apparent (isotropic) photon luminosity is ~22L_E (where L_E is the Eddington luminosity) in the face-on view. Even higher apparent luminosity is feasible if we increase the flow density. In model B with a moderate density, radiative cooling of the accretion flow is so efficient that a standard-type, cold, and geometrically thin disk is formed at radii greater than ~7R_S (where R_S is the Schwarzschild radius), while the flow is radiatively inefficient otherwise. The magnetic-pressure-driven disk wind appears in this model. In model C the density is too low for the flow to be radiatively efficient. The flow thus becomes radiatively inefficient accretion flow, which is geometrically thick and optically thin. The magnetic-pressure force, in cooperation with the gas-pressure force, drives outflows from the disk surface, and the flow releases its energy via jets rather than via radiation. Observational implications are briefly discussed.