Growth of Magnetorotational Instability in Circumstellar Disks around Class 0 Protostars

TL;DR

This study models the growth of magnetorotational instability in early-stage circumstellar disks around Class 0 protostars, revealing limited MRI activity within 20 au and potential activity farther out under specific magnetic conditions.

Contribution

It provides a detailed analysis of MRI growth considering chemical reactions, ionization, and dust effects in protostellar disks, highlighting the limited MRI development in early disks.

Findings

MRI active regions may exist far from the protostar with weak magnetic fields.

Disks within 20 au are stable against MRI, limiting turbulence development.

Dust size distribution influences diffusion coefficients and MRI growth.

Abstract

We investigate the possibility of the growth of magnetorotational instability (MRI) in disks around Class 0 protostars. We construct a disk model and calculate the chemical reactions of neutral and charged atoms, molecules and dust grains to derive the abundance of each species and the ionization degree of the disk. Then, we estimate the diffusion coefficients of non-ideal magnetohydrodynamics effects such as ohmic dissipation, ambipolar diffusion and the Hall effect. Finally, we evaluate the linear growth rate of MRI in each area of the disk. We investigate the effect of changes in the strength and direction of the magnetic field in our disk model and we adopt four different dust models to investigate the effect of dust size distribution on the diffusion coefficients. Our results indicate that an MRI active region possibly exists with a weak magnetic field in a region far from the protostar where the Hall effect plays a role in the growth of MRI. On the other hand, in all models the disk is stable against MRI in the region within $<20$ au from the protostar on the equatorial plane. Since the size of the disks in the early stage of star formation is limited to $\lesssim 10-$$20$ au, it is difficult to develop MRI-driven turbulence in such disks.