Vertical shear instability in accretion disc models with radiation transport

TL;DR

This study investigates the vertical shear instability (VSI) in accretion discs, demonstrating its potential to generate sustained, albeit low-level, turbulence in discs with radiative effects and stellar irradiation, using multi-dimensional hydrodynamic simulations.

Contribution

The paper provides a detailed analysis of VSI in accretion discs with radiative transport and irradiation, highlighting its role in turbulence generation beyond magneto-rotational instability.

Findings

VSI produces sustained turbulence with α ≈ 10^{-4} in isothermal discs.

Radiative cooling terminates turbulence unless stellar irradiation is present.

Irradiated discs exhibit similar low-level turbulence driven by VSI.

Abstract

The origin of turbulence in accretion discs is still not fully understood. While the magneto-rotational instability is considered to operate in sufficiently ionized discs, its role in the poorly ionized protoplanetary disc is questionable. Recently, the vertical shear instability (VSI) has been suggested as a possible alternative. Our goal is to study the characteristics of this instability and the efficiency of angular momentum transport, in extended discs, under the influence of radiative transport and irradiation from the central star. We use multi-dimensional hydrodynamic simulations to model a larger section of an accretion disc. First we study inviscid and weakly viscous discs using a fixed radial temperature profile in two and three spatial dimensions. The simulations are then extended to include radiative transport and irradiation from the central star. In agreement with previous studies we find for the isothermal disc a sustained unstable state with a weak positive angular momentum transport of the order of $\alpha \approx 10^{-4}$. Under the inclusion of radiative transport the disc cools off and the turbulence terminates. For discs irradiated from the central star we find again a persistent instability with a similar $\alpha$ value as for the isothermal case. We find that the VSI can indeed generate sustained turbulence in discs albeit at a relatively low level with $\alpha$ about few times $10^{-4}$