Magnetic Fields in Population III Star Formation

TL;DR

This study uses cosmological simulations to examine how magnetic fields grow during Population III star formation, highlighting the importance of numerical resolution for capturing dynamo amplification and revealing hydrodynamic effects on disk formation.

Contribution

It demonstrates the critical resolution needed to accurately model magnetic field amplification via dynamo action in Population III star formation simulations.

Findings

Turbulent motions can amplify seed magnetic fields if resolution is sufficient.

Higher resolution alters collapse dynamics, increasing temperatures and infall velocities.

Disk formation is suppressed at higher resolutions, affecting early star formation processes.

Abstract

We study the buildup of magnetic fields during the formation of Population III star-forming regions, by conducting cosmological simulations from realistic initial conditions and varying the Jeans resolution. To investigate this in detail, we start simulations from identical initial conditions, mandating 16, 32 and 64 zones per Jeans length, and studied the variation in their magnetic field amplification. We find that, while compression results in some amplification, turbulent velocity fluctuations driven by the collapse can further amplify an initially weak seed field via dynamo action, provided there is sufficient numerical resolution to capture vortical motions (we find this requirement to be 64 zones per Jeans length, slightly larger than, but consistent with previous work run with more idealized collapse scenarios). We explore saturation of amplification of the magnetic field, which could potentially become dynamically important in subsequent, fully-resolved calculations. We have also identified a relatively surprising phenomena that is purely hydrodynamic: the higher-resolved simulations possess substantially different characteristics, including higher infall-velocity, increased temperatures inside 1000 AU, and decreased molecular hydrogen content in the innermost region. Furthermore, we find that disk formation is suppressed in higher-resolution calculations, at least at the times that we can follow the calculation. We discuss the effect this may have on the buildup of disks over the accretion history of the first clump to form as well as the potential for gravitational instabilities to develop and induce fragmentation.