Can magnetized turbulence set the mass scale of stars?

David Guszejnov; Michael Y. Grudić; Philip F. Hopkins; Stella S. R. Offner; Claude-André Faucher-Giguère

doi:10.1093/mnras/staa1883

paper

Can magnetized turbulence set the mass scale of stars?

arXiv:2002.01421 · doi:10.1093/mnras/staa1883

Abstract

Understanding the evolution of self-gravitating, isothermal, magnetized gas is crucial for star formation, as these physical processes have been postulated to set the initial mass function (IMF). We present a suite of isothermal magnetohydrodynamic (MHD) simulations using the GIZMO code, that resolve the formation of individual stars in giant molecular clouds (GMCs), spanning a range of Mach numbers found in observed GMCs. As in past works, the mean and median stellar masses are sensitive to numerical resolution, because they are sensitive to low-mass stars that contribute a vanishing fraction of the overall stellar mass. The {\em mass-weighted} median stellar mass $M_{50}$ becomes insensitive to resolution once turbulent fragmentation is well-resolved. Without imposing Larson-like scaling laws, our simulations find $M_{50} \propto M_{0} M^{- 3} α_{turb} SFE^{1/3}$ for GMC mass $M_{0}$ , sonic Mach number $M$ , virial parameter $α_{turb}$ , and star formation efficiency $SFE = M_{⋆} / M_{0}$ . This fit agrees well with previous IMF results from the RAMSES, ORION2, and SphNG codes. Although $M_{50}$ has no significant dependence on the magnetic field strength at the cloud scale, MHD is necessary to prevent a fragmentation cascade that results in non-convergent stellar masses. For initial conditions and SFE similar to star-forming GMCs in our Galaxy, we predict $M_{50}$ to be $> 20 M_{⊙}$ , an order of magnitude larger than observed ( $\sim 2 M_{⊙}$ ), together with an excess of brown dwarfs. Moreover, $M_{50}$ is sensitive to initial cloud properties and evolves strongly in time within a given cloud, predicting much larger IMF variations than are observationally allowed. We conclude that physics beyond MHD turbulence and gravity are necessary ingredients for the IMF.

arXiv commentNote that this version has erratum at the end (does not affect results) 18 pages, 17 figures

Can magnetized turbulence set the mass scale of stars?

Abstract

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