Protostellar collapse: regulation of the angular momentum and onset of an ionic precursor

TL;DR

This study uses 3D simulations to explore how magnetic fields, non-ideal MHD effects, and dust grain size influence angular momentum regulation, disk formation, and outflow initiation during protostellar collapse.

Contribution

It quantifies the effects of non-ideal MHD processes and dust grain size on magnetic braking, outflow strength, and ionic precursors in protostellar collapse simulations.

Findings

Mass influences magnetic braking in the pseudo-disk.

Reducing small grains enhances ambipolar diffusion and weakens magnetic braking.

A large ionic precursor with observable velocities is identified.

Abstract

Through the magnetic braking and the launching of protostellar outflows, magnetic fields play a major role in the regulation of angular momentum in star formation, which directly impacts the formation and evolution of protoplanetary disks and binary systems. The aim of this paper is to quantify those phenomena in the presence of non-ideal magnetohydrodynamics effects, namely the Ohmic and ambipola r diffusion. We perform three-dimensional simulations of protostellar collapses varying the mass of the prestellar dense core, the thermal support (the $\alpha$ ratio) and the dust grain size-distribu tion. The mass mostly influences the magnetic braking in the pseudo-disk, while the thermal support impacts the accretion rate and hence the properties of the disk. Removing the grains smaller than 0. 1 $\mu$m in the Mathis, Rumpl, Nordsieck (MRN) distribution enhances the ambipolar diffusion coefficient. Similarly to previous studies, we find that this change in the distribution reduces the magnet ic braking with an impact on the disk. The outflow is also significantly weakened. In either case, the magnetic braking largely dominates the outflow as a process to remove the angular momentum from t he disk. Finally, we report a large ionic precursor to the outflow with velocities of several km s$^{-1}$, which may be observable.