Hydromagnetic waves in a rare ionized gas and galactic magnetic fields

Abstract

Hydromagnetic waves in rare ionized gases are of interest in connexion with galactic magnetic fields, the heating of the corona and other astrophysical problems. Thus it has been suggested (cf. Fermi 1949) that the galaxies may possess magnetic fields of the order of 10 -5 gauss which may be produced as the result of hydromagnetic waves set up in a smaller field, whilst Alfvén (1947) has suggested that the high temperature of the corona may be due to Joule heating during the passage of hydromagnetic waves. However, in a rare ionized gas the mean free paths of the ions and electrons may be very much larger than the spiral radius in the magnetic field, and the assumption that the medium behaves as a good conductor of electricity requires examination. The problem is certainly pertinent for galactic magnetic fields on account of the very long free paths of the charges there.