Torus Dynamo Model for Study of Magnetic Fields in the Outer Rings of Galaxies
At present, there is essentially no doubt that magnetic fields of a few μG exist in some spiral galaxies. The fields are produced by a dynamo mechanism. Because the equations of the dynamo theory are quite complicated, a two-dimensional approximation is often used since the galactic disk is sufficiently thin, so it is possible to replace some partial derivatives with algebraic expressions. Some galaxies have outer rings in which magnetic fields may also exist. The generation of these fields can also be studied using a two-dimensional approximation, but because that approximation was not developed for rings, but for thin disks, in this case it only yields qualitative results. Therefore, a torus dynamo model is used to study this process. This model is used to analyze possible scenarios for the evolution of magnetic fields in outer rings. It is found that for motions that are not too intense, a field with a quadrupole symmetry is generated. For faster motions a dipole component of the field may develop, which is fundamentally impossible in the two-dimensional approximation.
Keywordsouter rings of galaxies: dynamo theory
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