Towards a New Standard Model for Black Hole Accretion

TL;DR

This paper reviews recent advances in black hole accretion disk theory, highlighting the importance of MHD stresses and vertical angular momentum transport, which modify disk structure and emission spectra, impacting mass accretion rate estimates.

Contribution

It introduces a new model incorporating magnetically-driven outflows that alter disk spectra and suggests standard models underestimate accretion rates.

Findings

Magnetohydrodynamic stresses are crucial for angular momentum transport.

Vertical transport affects the inner disk structure and emission.

Standard accretion models may underestimate true mass accretion rates.

Abstract

We briefly review recent developments in black hole accretion disk theory, emphasizing the vital role played by magnetohydrodynamic (MHD) stresses in transporting angular momentum. The apparent universality of accretion-related outflow phenomena is a strong indicator that large-scale MHD torques facilitate vertical transport of angular momentum. This leads to an enhanced overall rate of angular momentum transport and allows accretion of matter to proceed at an interesting rate. Furthermore, we argue that when vertical transport is important, the radial structure of the accretion disk is modified at small radii and this affects the disk emission spectrum. We present a simple model demonstrating how energetic, magnetically-driven outflows modify the emergent disk emission spectrum with respect to that predicted by standard accretion disk theory. A comparison of the predicted spectra against observations of quasar spectral energy distributions suggests that mass accretion rates inferred using the standard disk model may severely underestimate their true values.