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Astronomy Colloquium
Cosmic magnetogenesis: From spontaneously emitted aperiodic turbulent to ordered equipartition fields
Date: Thursday, September 26th
Time: 3:30 pm - 5:00 pm
Place: 4421 Sterling Hall
Speaker: Reinhard Schlickeiser, Ruhr-University Bochum, Germany
Nonmagnetized fully-ionized plasmas spontaneously emit aperiodic turbulent magnetic field fluctuations. Its fluctuation intensities are dominated by the contribution from a recently found collective, damped mode, which modifies the earlier estimate of the total magnetic field strength to $|delta B|=24beta _e^{1/4}(gn_em_ec^2)^{1/2}$ G in the case of no collisional damping, where $g$ denotes the plasma parameter, $beta _e$ the thermal electron velocity in units of $c$ and $n_e$ the electron density. Accounting for simultaneous viscous damping reduces the estimate to $|delta B|=2305g(n_em_ec^2)^{1/2}$ G. For the unmagnetized intergalactic medium, immediately after the reionization onset, the field strengths from this mechanism are about $6.8cdot 10^{-13}$ G for no collisional damping and $1.5cdot 10^{-16}$ G for viscous damping. Maximum spatial scales of $10^{15}$ cm of the emitted aperiodic fluctuations are possible. These guaranteed magnetic fields in the form of randomly distributed fluctuations, produced by the spontaneous emission of the isotropic, thermal IGM plasma, may serve as seed fields for possible amplification by later possible plasma instabilities from anisotropic plasma particle distributions functions, MHD instabilities and/or the MHD dynamo process. Because of the high turbulent plasma beta, the seed fields are tied passively to the highly conducting IGM plasma as frozen-in magnetic fluxes, and therefore are subject to subsequent hydrodynamical shear or compression of the IGM medium from the shock waves of the supernova explosions of the first stars at the end of their lifetimes, or from supersonic stellar and galactic winds.
Host: Prof Alexander Lazarian
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