Growth of magnetorotational instability in circumstellar discs around class 0 protostars

Abstract

ABSTRACT We investigate the possibility of the growth of magnetorotational instability (MRI) in discs around Class 0 protostars. We construct a disc 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 disc. 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 disc. We investigate the effect of changes in the strength and direction of the magnetic field in our disc 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 disc is stable against MRI in the region within <20 au from the protostar on the equatorial plane. Since the size of the discs in the early stage of star formation is limited to ≲10–20 au, it is difficult to develop MRI-driven turbulence in such discs.