# The Role of Magnetic Fields in Setting the Star Formation Rate and the Initial Mass Function

## TL;DR

Magnetic fields influence star formation and the initial mass function mainly indirectly through feedback processes, with their direct effects being relatively minor according to current simulations.

## Contribution

This review highlights the limited direct impact of magnetic fields on star formation rates and the IMF, emphasizing their potential indirect effects via feedback mechanisms.

## Key findings

- Magnetic fields change SFR and IMF by factors of 2-3 in simulations.
- Indirect effects of magnetic fields via feedback could be significantly larger.
- Current evidence suggests magnetic fields are minor direct players in star formation.

## Abstract

Star-forming gas clouds are strongly magnetized, and their ionization fractions are high enough to place them close to the regime of ideal magnetohydrodyamics on all but the smallest size scales. In this review we discuss the effects of magnetic fields on the star formation rate (SFR) in these clouds, and on the mass spectrum of the fragments that are the outcome of the star formation process, the stellar initial mass function (IMF). Current numerical results suggest that magnetic fields by themselves are minor players in setting either the SFR or the IMF, changing star formation rates and median stellar masses only by factors of $\sim 2-3$ compared to non-magnetized flows. However, the indirect effects of magnetic fields, via their interaction with star formation feedback in the form of jets, photoionization, radiative heating, and supernovae, could have significantly larger effects. We explore evidence for this possibility in current simulations, and suggest avenues for future exploration, both in simulations and observations.