The Magnetic Field of the Milky Way

Abstract

Since its discovery 40 years ago as a confiner of cosmic rays and an aligner of interstellar dust grains, the Galactic magnetic field has been studied through emission and polarization of synchrotron radiation, Faraday rotation, Zeeman splitting, and effects on gas flows and morphology. The local field has a coherent, few microgauss, component roughly along the local spiral arm and a comparable chaotic component. Field direction in the plane is reversed one or more times both inside and outside the solar circle. Loops and spurs extend outside the plane and may merge with a general dipole, which is most conspicuous near the Galactic center. There may be a separate thick disc magneto-ionic component. Comparison with other galaxies, especially grand design vs. flocculent spirals should eventually prove fruitful. Parameters are not currently well enough known to rule out dipole or primordial origin.