Magnetic Phenomena

Abstract

The magnetic field within about 100 pc of the Galactic nucleus manifests itself in several directly observable ways. We review inferences about the magnetic field there drawn from the morphology of radio structures, from the polarization of nonthermal radio emission and thermal far-infrared emission, and from the Zeeman effect. Most of the evidence is consistent with the hypothesis that the field is strong and has an apparently highly organized poloidal geometry. While the field could be concentrated into localized flux tubes or walls, the most straightforward hypothesis is that it is relatively pervasive and uniform throughout the region, except in dense clouds, where the inferred field directions generally differ from those in the intercloud medium. If the field is pervasive, it probably dominates the pressure balance of the region. The energy of the field can be tapped as a heat source for clouds and, via field fine reconnection or electric fields induced by moving clouds, as the source of the relativistic particles which illuminate the many filamentary structures with nonthermal emission. One model for the primordial origin of the central poloidal field — that of Sofue and Fujimoto — is considered in some detail.