Matthew R. Bate, Terrence S. Tricco, Daniel J. Price

full text pdf (2.0Mb), accepted to MNRAS 30th September 2013

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Abstract

We have performed smoothed particle radiation magnetohydrodynamics (SPRMHD) simulations of the collapse of rotating, magnetised molecular cloud cores to form protostars. The calculations follow the formation and evolution of the first hydrostatic core, the collapse to form a stellar core, the launching of outflows from both the first hydrostatic core and stellar cores, and the breakout of the stellar outflow from the remnant of the first core. We investigate the roles of magnetic fields and thermal feedback on the outflow launching process, finding that both magnetic and thermal forces contribute to the launching of the stellar outflow. We also follow the stellar cores until they grow to masses of up to 20 Jupiter-masses, and determine their properties. We find that at this early stage, before fusion begins, the stellar cores have radii of R with radial entropy profiles that increase outward (i.e. are convectively stable) and minimum entropies per baryon of in their interiors. The structure of the stellar cores is found to be insensitive to variations in the initial magnetic field strength. With reasonably strong initial magnetic fields, accretion on to the stellar cores occurs through inspiralling magnetised pseudo-discs with negligible radiative losses, as opposed to first cores which effectively radiate away the energy liberated in the accretion shocks at their surfaces. We find that magnetic field strengths of 10 kG can be implanted in stellar cores at birth.

Movies	Movies and images (c) 2013 Daniel Price, Terrence Tricco & Matthew Bate, released under a Creative Commons Attribution-Noncommercial-Share Alike 3.0 License. [directory listing of all movies here]
Outflows launched during the collapse of a molecular cloud core to form a star from Daniel Price on Vimeo. The movie shows the collapse of a gaseous sphere to form a protostar. The collapse stalls at the `first core' phase, launching an outflow of gas, before molecular Hydrogen dissociates and the collapse proceeds to form the second core, the protostar, with a density close to that of water (1 g/cm^3) Click for downloadable Quicktime .mov
Outflows launched during the collapse of a molecular cloud core to form a star (with weak magnetic fields) from Daniel Price on Vimeo. As above, but with weaker initial magnetic fields. Click for downloadable Quicktime .mov
Snapshots from the calculations: