The Galactic Center Magnetosphere

TL;DR

This paper reviews the magnetic field in the Galactic Center, discussing its structures, strength estimates, and influence on galactic dynamics, concluding that a pervasive, strong magnetic field likely exists in the region.

Contribution

It provides a comprehensive overview of observational evidence and debates regarding the magnetic field's strength, structure, and pervasiveness in the Galactic Center.

Findings

Magnetic structures include nonthermal radio filaments and helically wound formations.

Field strength estimates range from tens of microgauss to about a milligauss.

Current evidence supports a pervasive, strong magnetic field influencing galactic phenomena.

Abstract

The magnetic field within a few hundred parsecs of the center of the Galaxy is an essential component of any description of that region. The field has several pronounced observational manifestations: 1) morphological structures such as nonthermal radio filaments (NTFs) -- magnetic flux tubes illuminated by synchrotron emission from relativistic electrons -- and a remarkable, large-scale, helically wound structure, 2) relatively strong polarization of thermal dust emission from molecular clouds, presumably resulting from magnetic alignment of the rotating dust grains, and 3) synchrotron emission from cosmic rays. Because most of the NTFs are roughly perpendicular to the Galactic plane, the implied large-scale geometry of the magnetic field is dipolar. Estimates of the mean field strength vary from tens of microgauss to ~ a milligauss. The merits and weaknesses of the various estimations are discussed here. If the field strength is comparable to a milligauss, then the magnetic field is able to exert a strong influence on the dynamics of molecular clouds, on the collimation of a Galactic wind, and on the lifetimes and bulk motions of relativistic particles. Related to the question of field strength is the question of whether the field is pervasive throughout the central zone of the Galaxy, or whether its manifestations are predominantly localized phenomena. Current evidence favors the pervasive model.