Magnetic Fields in the Early Universe

Abstract

Primordial turbulence in the radiation-dominated era of the early Universe has an associated weak seed magnetic field on all scales of the turbulence. This seed field is stochastically amplified by the small-scale rapidly fluctuating turbulence motions and it is possible, in principle at least, for magnetic and small-scale kinetic energies to attain equipartition within an expansion time. It is unlikely that the magnetic energy attains equipartition with the large-scale kinetic energy of the turbulence. The intensity of the field is ~ 10 9 Gauss at temperature T = 10 9 K and ~ 10 2 Gauss at T = 10 5 K. Field generation ceases at approximately the epoch of equal radiation and matter densities. Some implications of the primordially generated field are considered. It is shown that the Jeans mass, owing to magnetic stresses, is of galactic magnitude and plays a crucial role in galaxy formation. It is estimated that the present intergalactic magnetic field has an intensity of ~ 10 −8 Gauss and a dominant scale-length ~ 10 kpc. Some brief comments are made on the possibility of ion acceleration by agitated magnetic fields during and after the radiation era.