# The dependence of protostar formation on the geometry and strength of the initial magnetic field

## TL;DR

This study uses simulations to explore how the initial magnetic field's strength and geometry influence protostar formation, outflow structures, and system configurations, revealing significant effects on star and binary formation processes.

## Contribution

It provides new insights into how magnetic field parameters affect protostellar collapse, outflows, and system morphology, using detailed magnetohydrodynamics simulations.

## Key findings

- Magnetic field strength influences binary formation likelihood.
- Field geometry affects outflow suppression and disc warping.
- Outflow speeds do not exceed 8 km/s in the simulations.

## Abstract

We report results from twelve simulations of the collapse of a molecular cloud core to form one or more protostars, comprising three field strengths (mass-to-flux ratios, {\mu}, of 5, 10, and 20) and four field geometries (with values of the angle between the field and rotation axes, {\theta}, of 0{\deg}, 20{\deg}, 45{\deg}, and 90{\deg}), using a smoothed particle magnetohydrodynamics method. We find that the values of both parameters have a strong effect on the resultant protostellar system and outflows. This ranges from the formation of binary systems when {\mu} = 20 to strikingly differing outflow structures for differing values of {\theta}, in particular highly suppressed outflows when {\theta} = 90{\deg}. Misaligned magnetic fields can also produce warped pseudo-discs where the outer regions align perpendicular to the magnetic field but the innermost region re-orientates to be perpendicular to the rotation axis. We follow the collapse to sizes comparable to those of first cores and find that none of the outflow speeds exceed 8 km s$^{-1}$. These results may place constraints on both observed protostellar outflows, and also on which molecular cloud cores may eventually form either single stars and binaries: a sufficiently weak magnetic field may allow for disc fragmentation, whilst conversely the greater angular momentum transport of a strong field may inhibit disc fragmentation.