Driving Disk Winds and Heating up Hot Coronae by MRI Turbulence

TL;DR

This study uses 3D MHD simulations to explore how MRI turbulence can generate hot coronae and drive disk winds in accretion disks, revealing the impact of thermal physics on wind driving mechanisms.

Contribution

It demonstrates that non-isothermal conditions lead to the formation of hot coronae and alter wind driving from magnetic to gas pressure, advancing understanding of disk wind origins.

Findings

Coronae form at >1-2 scale heights with gamma >~ 1.1.

Disk winds shift from magnetic to gas pressure driven in non-isothermal cases.

Density fluctuations are larger in non-isothermal simulations.

Abstract

We investigate the formation of hot coronae and vertical outflows in accretion disks by magneto-rotational turbulence. We perform local three-dimensional (3D) MHD simulations with the vertical stratification by explicitly solving an energy equation with various effective ratios of specific heats, gamma. Initially imposed weak vertical magnetic fields are effectively amplified by magnetorotational instability (MRI) and winding due to the differential rotation. In the isothermal case (gamma=1), the disk winds are mainly driven by the Poynting flux associated with the MHD turbulence and show quasi-periodic intermittency. On the other hand, in the non-isothermal cases with gamma >~ 1.1, the regions above 1-2 scale heights from the midplane are effectively heated up to form coronae with the temperature of ~ 50 times of the initial value, which are connected to the cooler midplane region through the pressure-balanced transition regions. As a result, the disk winds are mainly driven by the gas pressure with exhibiting more time-steady nature, although the nondimensional time-averaged mass loss rates are similar to that of the isothermal case. Sound-like waves are confined in the cool midplane region in these cases, and the amplitude of the density fluctuations is larger than that of the isothermal case.