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The Galactic Dynamo: Modes and Models

Published online by Cambridge University Press:  19 July 2016

G. Rüdiger ,
D. Elstner  and
M. Schultz
G. Rüdiger
Affiliation:
Astrophysikalisches Institut Potsdam An der Sternwarte 16, D-O-1590 Potsdam, Germany
D. Elstner
Affiliation:
Astrophysikalisches Institut Potsdam An der Sternwarte 16, D-O-1590 Potsdam, Germany
M. Schultz
Affiliation:
Astrophysikalisches Institut Potsdam An der Sternwarte 16, D-O-1590 Potsdam, Germany

Abstract

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The hitherto known essentials of the present-day dynamo theory of the galactic magnetic fields are reported. The vertical stratification of the interstellar turbulence is exclusively considered as the source of the α-effect. New expressions for this tensorial effect and its quenching by the field are applied. Although its anisotropy and the influence of the halo easily yield the excitation of non-axisymmetric magnetic configurations of diverse equatorial symmetry, the galactic differential rotation finally leads to axisymmetric and quadrupolar solutions. The magnetic strength of the dynamo fields slightly exceeds the equipartition value while its angular momentum transport (into the intergalactic space) is very small.

For increasingly steep vertical gradients of the turbulence intensity a saturation of the field strength is found since the eddy diffusivity grows with the α-effect. Only beyond the maximum of the field the equatorial symmetry changes to an equatorial antisymmetry, i.e. to dipolar solutions.

In order to produce the observed values of the pitch angles one has only to choose correlation times of the turbulence slightly exceeding the usually accepted 107 yrs.

Type
8. Magnetic Fields in Galaxies: Dynamo Theory
Information
Symposium - International Astronomical Union , Volume 157: The Cosmic Dynamo , 1993 , pp. 321 - 331
Copyright
Copyright © Kluwer 1993 

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