Plasma instabilities and magnetic-field growth in clusters of galaxies

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  • 18 January 2005
Abstract
We show that, under very general conditions, cluster plasmas threaded by weak magnetic fields are subject to very fast growing plasma instabilities. These instabilities can amplify magnetic fields in clusters from seed strength of \~10^{-18} G to dynamically important strengths on cosmologically trivial time scales (<10^8 yr). The instabilities are driven by the anisotropies of the plasma pressure (viscous stress). Such an anisotropy will naturally arise in any weakly magnetized plasma that has low collisionality and is subject by stirring. This effect is captured by the extended MHD model with Braginskii viscosity. However, the instability growth rates are proportional to the wavenumber down to scales of the order of ion Larmor radius, so MHD equations with Braginskii viscosity are not well posed and a fully kinetic description is necessary.

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