Title:	The impact of thermodynamics on gravitational collapse: filament formation and magnetic field amplification
Authors:	Peters, Thomas Schleicher, Dominik R.G. Klessen, Ralf S. Banerjiee, Robi Federrath, Christoph Smith, Rowan J. Sur, Sharanya
Keywords:	ISM: kinematics and dynamics ISM: magnetic fields stars: formation
Issue Date:	Dec-2012
Publisher:	IOP Sciences for American Astronomical Society
Citation:	The Astrophysical Journal Letters, 2012, Vol.760, pL28
Abstract:	Stars form by the gravitational collapse of interstellar gas. The thermodynamic response of the gas can be characterized by an effective equation of state. It determines how gas heats up or cools as it gets compressed, and hence plays a key role in regulating the process of stellar birth on virtually all scales, ranging from individual star clusters up to the galaxy as a whole. We present a systematic study of the impact of thermodynamics on gravitational collapse in the context of high-redshift star formation, but argue that our findings are also relevant for present-day star formation in molecular clouds. We consider a polytropic equation of state, P = kρΓ, with both sub-isothermal exponents Γ < 1 and super-isothermal exponents Γ > 1. We find significant differences between these two cases. For Γ > 1, pressure gradients slow down the contraction and lead to the formation of a virialized, turbulent core. Weak magnetic fields are strongly tangled and efficiently amplified via the small-scale turbulent dynamo on timescales corresponding to the eddy-turnover time at the viscous scale. For Γ < 1, on the other hand, pressure support is not sufficient for the formation of such a core. Gravitational contraction proceeds much more rapidly and the flow develops very strong shocks, creating a network of intersecting sheets and extended filaments. The resulting magnetic field lines are very coherent and exhibit a considerable degree of order. Nevertheless, even under these conditions we still find exponential growth of the magnetic energy density in the kinematic regime.
Description:	Restricted Access. An open-access version is available at arXiv.org (one of the alternative locations)
URI:	http://hdl.handle.net/2289/5383
ISSN:	0004-637X 1538-4357 (online)
Alternative Location:	http://dx.doi.org/10.1088/2041-8205/760/2/l28 http://arxiv.org/abs/1209.5861
Copyright:	2012 The American Astronomical Society.
Appears in Collections:	Research Papers (A&A)

Items in RRI Digital Repository are protected by copyright, with all rights reserved, unless otherwise indicated.