Galactic Fields and Fountains

Supernovae of type II occur in the galactic disk at the rate of about three per century. The interstellar gas lying within some 80 pc is disturbed by a supernova explosion. In each event a mass of some 126 solar masses gains so much entropy that it stays hot long enough to escape from the galactic disk. The combined effect of many explosions produces a fountain flow, which can rise to some 4 kpc, and then returns to the plane. Over a period of about 520 million years all the interstellar matter becomes involved in this flow. The interstellar medium is a good conductor of electricity, and is frozen to the magnetic lines of force to which it is linked. The fountain flow, and the subsequent return to the galactic disk, provide a means by which the field is redistributed among the interstellar medium and have an important effect on any possible dynamo mechanism.