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Title:
Plasma Instabilities and Magnetic Field Growth in Clusters of Galaxies
Authors:
Schekochihin, A. A.; Cowley, S. C.; Kulsrud, R. M.; Hammett, G. W.; Sharma, P.
Affiliation:
AA(Department of Applied Mathematics and Theoretical Physics, University of Cambridge, Wilberforce Road, Cambridge CB3 0WA, UK ), AB(Department of Physics and Astronomy, UCLA, Los Angeles, CA 90095-1547 and Plasma Physics Group, Imperial College London, Blackett Laboratory, Prince Consort Road, London SW7 2BW, UK.), AC(Plasma Physics Laboratory, Princeton University, P. O. Box 451, Princeton, NJ 08543.), AD(Plasma Physics Laboratory, Princeton University, P. O. Box 451, Princeton, NJ 08543.), AE(Plasma Physics Laboratory, Princeton University, P. O. Box 451, Princeton, NJ 08543.)
Publication:
The Astrophysical Journal, Volume 629, Issue 1, pp. 139-142. (ApJ Homepage)
Publication Date:
08/2005
Origin:
UCP
Astronomy Keywords:
Galaxies: Clusters: General, Instabilities, Magnetic Fields, Magnetohydrodynamics: MHD, Plasmas, Turbulence
DOI:
10.1086/431202
Bibliographic Code:
2005ApJ...629..139S

Abstract

We show that under very general conditions, cluster plasmas threaded by weak magnetic fields are subject to very fast growing plasma instabilities driven by the anisotropy of the plasma pressure (viscous stress) with respect to the local direction of the magnetic field. Such an anisotropy will naturally arise in any weakly magnetized plasma that has low collisionality and is subject to stirring. The magnetic field must be sufficiently weak for the instabilities to occur, viz., β>~Re1/2. The instabilities are captured by the extended MHD model with Braginskii viscosity. However, their growth rates are proportional to the wavenumber down to the ion gyroscale, so MHD equations with Braginskii viscosity are not well posed and a fully kinetic treatment is necessary. The instabilities can lead to magnetic fields in clusters being amplified from seed strength of ~10-18 G to dynamically important strengths of ~10 μG on cosmologically trivial timescales (~108 yr). The fields produced during the amplification stage are at scales much smaller than observed. Predicting the saturated field scale and structure will require a kinetic theory of magnetized cluster turbulence.
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