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Magnetic fields during primordial star formation

By Dominik R. G. Schleicher, Sharanya Sur, Robi Banerjee, Ralf S. Klessen, Christoph Federrath, Tigran Arshakian, Rainer Beck and Marco Spaans

Abstract

Recent FERMI observations provide a lower limit of 10^{-15} G for the magnetic field strength in the intergalactic medium (IGM). This is consistent with theoretical expectations based on the Biermann battery effect, which predicts such IGM fields already at redshifts z~10. During gravitational collapse, such magnetic fields can be amplified by compression and by turbulence, giving rise to the small-scale dynamo. On scales below the Jeans length, the eddy turnover timescale is much shorter than the free-fall timescale, so that saturation can be reached during collapse. This scenario has been tested and confirmed with magneto-hydrodynamical simulations following the collapse of a turbulent, weakly magnetized cloud. Based on a spectral analysis, we confirm that turbulence is injected on the Jeans scale. For the power spectrum of the magnetic field, we obtain the Kazantsev slope which is characteristic for the small-scale dynamo. A calculation of the critical length scales for ambipolar diffusion and Ohmic dissipation shows that these scales are always small enough to allow significant amplification of the magnetic field by small-scale eddies. We discuss potential implications for the protostellar accretion disk, with particular focus on the magneto-rotational instability, which may change the morphology of the disk and reduce the accretion rate by a factor of a few.Comment: 4 pages, 2 figures, conference proceedings from "Cosmic Radiation Fields: Sources in the early Universe", 2010, Hamburg, German

Topics: Astrophysics - Cosmology and Nongalactic Astrophysics
Year: 2011
OAI identifier: oai:arXiv.org:1102.3558
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