Origin of Magnetic Fields in the Early Universe

Primordial turbulence in the radiation era generates a weak seed magnetic field on all scales of the turbulence. This field is stochastically amplified by turbulence motions, and it is possible for magnetic and small-scale kinetic energies to attain equipartition within an expansion time. Field generation ceases at the epoch of equal radiation and matter densities, when the field strength is of the order of 1 G. It is estimated that the present intergalactic magnetic field has an intensity of ∼${10}^{-8\mathrm{}}$ G and a scale-length of ∼Mparsec.