Accretion in Radiative Equipartition (AiRE) Disks

TL;DR

This paper proposes AiRE disks, a modified accretion disk model where radiation and gas pressures are in equipartition, addressing thermal instability issues in radiation pressure dominated regimes and impacting black hole growth and X-ray binary states.

Contribution

The paper introduces AiRE disks, a new model with radiation and gas pressure equipartition, altering disk stability and properties compared to standard models.

Findings

AiRE disks are stable in radiation pressure dominated regions.

Accretion rate limits are set by Toomre and sonic point instabilities.

Implications for black hole mass limits and X-ray binary state transitions.

Abstract

Standard accretion disk theory (Shakura & Sunyaev 1973) predicts that the total pressure in disks at typical (sub-)Eddington accretion rates becomes radiation pressure dominated. However, radiation pressure dominated disks are thermally unstable. Since these disks are observed in approximate steady state over the instability time-scale, our accretion models in the radiation pressure dominated regime (i.e. inner disk) need to be modified. Here, we present a modification to the SS model, where radiation pressure is in equipartition with gas pressure in the inner region. We call these flows Accretion in Radiative Equipartition (AiRE) Disks. We introduce the basic features of AiRE disks and show how they modify disk properties such as the Toomre parameter and central temperature. We then show that the accretion rate of AiRE disks is limited from above and below, by Toomre and nodal sonic point instabilities, respectively. The former leads to a strict upper limit on the mass of supermassive black holes as a function of cosmic time (and spin), while the latter could explain the transition between hard and soft states of X-ray binaries.