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Fast growth of magnetic fields in galaxy clusters: a self‐accelerating dynamo
Author(s) -
Schekochihin A. A.,
Cowley S. C.
Publication year - 2006
Publication title -
astronomische nachrichten
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.394
H-Index - 63
eISSN - 1521-3994
pISSN - 0004-6337
DOI - 10.1002/asna.200610600
Subject(s) - physics , dynamo , intracluster medium , reynolds number , galaxy , galaxy cluster , magnetic reynolds number , cluster (spacecraft) , magnetic field , astrophysics , field (mathematics) , explosive material , mechanics , turbulence , chemistry , mathematics , organic chemistry , quantum mechanics , pure mathematics , computer science , programming language
We propose a model of magnetic‐field growth in galaxy clusters whereby the field is ampli.fied by a factor of about 10 8 over a cosmologically short time of ∼ 10 8 yr. Our model is based on the idea that the viscosity of the intracluster medium during the field‐amplification epoch is determined not by particle collisions but by plasma microinstabilities: these give rise to small‐scale .uctuations, which scatter particles, increasing their effective collision rate and, therefore, the effective Reynolds number. This gives rise to a bootstrap effect as the growth of the field triggers the instabilities which increase the Reynolds number which, in turn, accelerates the growth of the field. The growth is explosive and the result is that the observed field strength is reached over a fraction of the cluster lifetime independent of the exact strength of the seed field (which only needs to be above ∼ 10 –15 G to trigger the explosive growth). (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)