Title:	Magnetic field amplification during gravitational collapse - influence of turbulence, rotation and gravitational compression
Authors:	Sur, Sharanya Federrath, Christoph Schhleicher, Dominik R.G. Banerjee, Robi Klessen, Ralf S.
Keywords:	magnetic fields turbulence stars formation numerical
Issue Date:	4-Jul-2012
Publisher:	Oxford University Press on behalf of the Royal Astronomical Society
Citation:	Monthly Notices of Royal Astronomical Society, 2012, Vol. 423, p3148
Abstract:	We study the influence of initial conditions on the magnetic field amplification during the collapse of a magnetised gas cloud. We focus on the dependence of the growth and saturation level of the dynamo generated field on the turbulent properties of the collapsing cloud. In particular, we explore the effect of varying the initial strength and injection scale of turbulence and the initial uniform rotation of the collapsing magnetised cloud. In order to follow the evolution of the magnetic field in both the kinematic and the nonlinear regime, we choose an initial field strength of $\simeq 1\,\mkG$ with the magnetic to kinetic energy ratio, Em/Ek∼10−4. Both gravitational compression and the small-scale dynamo initially amplify the magnetic field. Further into the evolution, the dynamo-generated magnetic field saturates but the total magnetic field continues to grow because of compression. The saturation of the small-scale dynamo is marked by a change in the slope of B/ρ2/3 and by a shift in the peak of the magnetic energy spectrum from small scales to larger scales. For the range of initial Mach numbers explored in this study, the dynamo growth rate increases as the Mach number increases from vrms/cs∼0.2 to 0.4 and then starts decreasing from vrms/cs∼1.0. We obtain saturation values of Em/Ek=0.2−0.3 for these runs. Simulations with different initial injection scales of turbulence also show saturation at similar levels. For runs with different initial rotation of the cloud, the magnetic energy saturates at Em/Ek∼0.2−0.4 of the equipartition value. (Abridged)
Description:	Restricted Access. An open-access version is available at arXiv.org (one of the alternative locations)
URI:	http://hdl.handle.net/2289/7889
ISSN:	0035-8711 1365-2966 (Online)
Alternative Location:	https://ui.adsabs.harvard.edu/abs/2012MNRAS.423.3148S/abstract https://arxiv.org/abs/1202.3206 http://dx.doi.org/10.1111/j.1365-2966.2012.21100.x
Copyright:	2012 The Author(s)
Appears in Collections:	Research Papers (A&A)

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