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J. Maron, E. Blackman (University of Rochester), A. Schekochihin (Cambridge University), G. Field (Harvard University), B. Chandran (University of Iowa), S. Cowley (Imperial College, London), J. McWilliams (UCLA)
The Galactic magnetic field has an energy density comparable to that of interstellar medium turbulence and a coherence exceeding 1000 parsecs. We will discuss possible scenarios for its formation by a helical or nonhelical turbulent dynamo. The nature of forced MHD turbulence, the magnetic analogue of the Kolmogorov cascade for hydrodynamic turbulence, plays a key role. Our chief results are that turbulence without a coherent kinetic helicity can generate large energy but not large scale magnetic fields. The magnetic energy peak approaches the resistive scale in the long-term steady state. However, we find that turbulence with a coherent kinetic helicity, such as can arise from Galactic rotation and density stratification, is a good candidate for generating the coherent large scale magnetic fields within a Hubble time. Even though the magnetic resistivity is so small so as to enforce magnetic helicity conservation, Galactic-scale magnetic helicity can be generated by exchanging magnetic helicity between the Galactic and the supernova forcing scale. Before the build-up of small scale current helicity quenches the field growth, significant large scale Galactic fields have already been generated. Funded by the DOE and the NSF.
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The author(s) of this abstract have provided an email address for comments about the abstract: maron@tapir.caltech.edu
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Bulletin of the American Astronomical Society, 36 #2
© 2004. The American Astronomical Soceity.