The effect of magnetic fields on the formation of circumstellar discs around young stars

TL;DR

This paper uses advanced MHD-SPH simulations to study how magnetic fields influence the size, mass, and stability of circumstellar discs and binary star formation, revealing magnetic pressure's dominant role.

Contribution

It introduces a new MHD-SPH simulation method and demonstrates how magnetic fields affect disc formation and binary fragmentation, highlighting the importance of magnetic pressure and orientation.

Findings

Magnetic fields produce smaller, less massive discs less prone to gravitational instability.

Magnetic fields suppress fragmentation in binary star formation.

Magnetic pressure dominates over magnetic tension effects.

Abstract

We present first results of our simulations of magnetic fields in the formation of single and binary stars using a recently developed method for incorporating Magnetohydrodynamics (MHD) into the Smoothed Particle Hydrodynamics (SPH) method. An overview of the method is presented before discussing the effect of magnetic fields on the formation of circumstellar discs around young stars. We find that the presence of magnetic fields during the disc formation process can lead to significantly smaller and less massive discs which are much less prone to gravitational instability. Similarly in the case of binary star formation we find that magnetic fields, overall, suppress fragmentation. However these effects are found to be largely driven by magnetic pressure. The relative importance of magnetic tension is dependent on the orientation of the field with respect to the rotation axis, but can, with the right orientation, lead to a dilution of the magnetic pressure-driven suppression of fragmentation.