Spontaneous Discontinuities in Galactic Magnetic Fields and the Creation of Galactic X-ray Halos

Abstract

The magnetic field in the gaseous disk of the galaxy is dynamically unstable to undulations with wavelengths of the order of 1 kpc. The elevated portions of the field are subject to rapid inflation (~ 50 km/sec) by the cosmic rays produced within the gaseous disk. The result is a magnetic halo of 1–3 × 10−6 gauss, composed of close packed bipolar lobes of field extending outward from the surface of the disk to distances of several kpc. The inflation is presumably irregular, producing tangential discontinuities (current sheets) throughout the extended bipolar fields. A major portion of the magnetic energy is dissipated by rapid reconnection at these current sheets, heating the tenuous halo gas to temperatures of 106 − 107 °K and producing the X-ray emission observed from the halos of many spiral galaxies.