GROWTH OF A LOCALIZED SEED MAGNETIC FIELD IN A TURBULENT MEDIUM

Turbulence dynamo deals with the amplification of a seed magnetic field in a turbulent medium and has been studied mostly for uniform or spatially homogeneous seed magnetic fields. However, some astrophysical processes (e.g., jets from active galaxies, galactic winds, or ram-pressure stripping in ga...

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Bibliographic Details
Published in:The Astrophysical journal 2012-11, Vol.759 (2), p.1-10, Article 91
Main Authors: CHO, Jungyeon, YOO, Hyunju
Format: Article
Language:English
Subjects:
AMPLIFICATION
ASTRONOMY
ASTROPHYSICS
ASTROPHYSICS, COSMOLOGY AND ASTRONOMY
Computational fluid dynamics
DIFFUSION
Earth, ocean, space
ENERGY DENSITY
Exact sciences and technology
FILAMENTS
Fluid flow
Galactic clusters
GALAXIES
GALAXY CLUSTERS
INTERSTELLAR MAGNETIC FIELDS
JETS
Magnetic fields
MAGNETOHYDRODYNAMICS
PRANDTL NUMBER
Seeds
STELLAR WINDS
TURBULENCE
Turbulent flow
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Summary:Turbulence dynamo deals with the amplification of a seed magnetic field in a turbulent medium and has been studied mostly for uniform or spatially homogeneous seed magnetic fields. However, some astrophysical processes (e.g., jets from active galaxies, galactic winds, or ram-pressure stripping in galaxy clusters) can provide localized seed magnetic fields. In this paper, we numerically study amplification of localized seed magnetic fields in a turbulent medium. Throughout the paper, we assume that the driving scale of turbulence is comparable to the size of the system. Our findings are as follows. First, turbulence can amplify a localized seed magnetic field very efficiently. The growth rate of magnetic energy density is as high as that for a uniform seed magnetic field. This result implies that magnetic field ejected from an astrophysical object can be a viable source of a magnetic field in a cluster. Second, the localized seed magnetic field disperses and fills the whole system very fast. If turbulence in a system (e.g., a galaxy cluster or a filament) is driven at large scales, we expect that it takes a few large-eddy turnover times for the magnetic field to fill the whole system. Third, growth and turbulence diffusion of a localized seed magnetic field are also fast in high magnetic Prandtl number turbulence. Fourth, even in decaying turbulence, a localized seed magnetic field can ultimately fill the whole system. Although the dispersal rate of the magnetic field is not fast in purely decaying turbulence, it can be enhanced by an additional forcing.
ISSN:0004-637X
1538-4357
DOI:10.1088/0004-637X/759/2/91