Primordial magnetic fields in Population III star formation: a magnetised resolution study

TL;DR

This study investigates whether primordial magnetic fields influence Population III star formation and finds that magnetic fields do not significantly affect gas fragmentation or star formation outcomes in simulations.

Contribution

It introduces a saturated magnetic field at equipartition in simulations to assess its impact on primordial star formation, a novel approach for this context.

Findings

Magnetic fields did not suppress gas fragmentation.

Number of sink particles was unaffected by magnetic fields.

Magnetic pressure remained sub-dominant to gas pressure.

Abstract

Population III stars form in groups due to the fragmentation of primordial gas. While uniform magnetic fields have been shown to support against fragmentation in present day star formation, it is unclear whether realistic k^3/2 primordial fields can have the same effect. We bypass the issues associated with simulating the turbulent dynamo by introducing a saturated magnetic field at equipartition with the velocity field when the central densities reaches 10-13 g cm-3. We test a range of sink particle creation densities from 10-10-10-8 g cm-3. Within the range tested, the fields did not suppress fragmentation of the gas and hence could not prevent the degree of fragmentation from increasing with increased resolution. The number of sink particles formed and total mass in sink particles was unaffected by the magnetic field across all seed fields and resolutions. The magnetic pressure remained sub-dominant to the gas pressure except in the highest density regions of the simulation box, where it became equal to but never exceeded gas pressure. Our results suggest that the inclusion of magnetic fields in numerical simulations of Pop III star formation is largely unimportant.