Smoothed particle magnetohydrodynamic simulations of protostellar outflows with misaligned magnetic field and rotation axes

TL;DR

This paper introduces a stable smoothed particle magnetohydrodynamics method to simulate protostellar outflows, revealing how the angle between magnetic and rotation axes influences outflow morphology and strength.

Contribution

It presents a new stable formalism for smoothed particle MHD simulations that allows smaller sink particles and explores the impact of magnetic field and rotation axis misalignment.

Findings

Outflows depend strongly on the angle between magnetic and rotation axes.

Jet-like outflows are absent when the angle exceeds 30 degrees.

Substantial outflows are not produced when the angle exceeds 60 degrees.

Abstract

We have developed a modified form of the equations of smoothed particle magnetohydrodynamics which are stable in the presence of very steep density gradients. Using this formalism, we have performed simulations of the collapse of magnetised molecular cloud cores to form protostars and drive outflows. Our stable formalism allows for smaller sink particles (< 5 AU) than used previously and the investigation of the effect of varying the angle, {\theta}, between the initial field axis and the rotation axis. The nature of the outflows depends strongly on this angle: jet-like outflows are not produced at all when {\theta} > 30{\deg}, and a collimated outflow is not sustained when {\theta} > 10{\deg}. No substantial outflows of any kind are produced when {\theta} > 60{\deg}. This may place constraints on the geometry of the magnetic field in molecular clouds where bipolar outflows are seen.