http://arxiv.org/abs/1512.06455
Magnetic fields pervade the entire Universe and, through their dynamical interactions with matter, affect the formation and evolution of astrophysical systems from cosmological to planetary scales. How primordial cosmological seed fields arose and were further amplified to $\mu$Gauss levels reported in nearby galaxy clusters, near equipartition with kinetic energy of plasma motions and on scales of at least tens of kiloparsecs, is a major theoretical puzzle still largely unconstrained by observations. Extragalactic plasmas are weakly collisional (as opposed to collisional magnetohydrodynamic fluids), and whether magnetic-field growth and its sustainment through an efficient dynamo instability driven by chaotic motions is possible in such plasmas is not known. Fully kinetic numerical simulations of the Vlasov equation in a six-dimensional phase space necessary to answer this question have until recently remained beyond computational capabilities. Here, we show by means of such simulations that magnetic-field amplification via a turbulent dynamo instability does occur in a stochastically-driven, non-relativistic subsonic flow of initially unmagnetized collisionless plasma. We also find that this collisionless dynamo self-accelerates and becomes entangled with kinetic instabilities as the plasma magnetization increases. These results suggest that a turbulent “plasma dynamo” can magnetize the intracluster medium up to near-equipartition levels on a timescale much shorter than the Hubble time, and emphasize the crucial role of multiscale kinetic physics in high-energy astrophysical plasmas.
F. Rincon, F. Califano, A. Schekochihin, et. al.
Tue, 22 Dec 15
75/78
Comments: Submitted. 5 pages, 5 figures, 2 movies (url links in manuscript)
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