Dynamos in Galaxies

Theoretical arguments provided the first definitive prediction for the existence of an interstellar magnetic field in our Galaxy: There was no other way to explain the observed isotropy of the cosmic radiation. Alfven, Richtmeyer and Teller (1949), and Fermi (1949) stated that the particles of the cosmic radiation have to be reflected often and this can hardly be explained other than by an interaction with a magnetic field.