Accretion disks around massive stars: Hydrodynamic structure, stability and dust sublimation

TL;DR

This paper models the hydrodynamic structure and stability of accretion disks around massive protostars, revealing extremely high inner disk temperatures, large dust sublimation radii, and implications for disk turbulence and stability.

Contribution

It provides a detailed steady-state thin disk model for massive protostars, incorporating dust and gas opacities, and explores the effects of turbulence and temperature on disk structure and stability.

Findings

Inner disk temperatures can reach ~10^5 K.

Dust sublimation radius exceeds 10 AU, larger than stellar irradiation predicts.

Disks are stable for turbulence parameter .1 up to 80 AU.

Abstract

We investigate the structure of accretion disks around massive protostar applying steady state models of thin disks. The thin disk equations are solved with proper opacities for dust and gas taking into account the huge temperature variation along the disk. We explore a wide parameter range concerning stellar mass, accretion rate, and viscosity parameter \alpha . The most essential finding is a very high temperature of the inner disk. For e.g. a 10 M_sun protostar and an accretion rate of 10^-4 M_sun/yr, the disk midplane temperature may reach almost 10^5 K. The disk luminosity in this case is about 10^4 L_sun and, thus, potentially higher than that of a massive protostar. We motivate our disk model with similarly hot disks around compact stars. We calculate a dust sublimation radius by turbulent disk self-heating of more than 10AU, a radius, which is 3 times larger than caused by stellar irradiation. We discuss implications of this result on the flashlight effect and the consequences for the radiation pressure of the central star. In difference to disks around low mass protostars our models suggest rather high values for the disk turbulence parameter \alpha close to unity. However, disk stability to fragmentation due to thermal effects and gravitational instability would require a lower \alpha value. For \alpha = 0.1 we find stable disks out to 80AU. Essentially, our model allows to compare the outer disk to some of the observed massive protostellar disk sources, and from that, extrapolate on the disk structure close to the star which is yet impossible to observe.