Cosmic magnetization: from spontaneously emitted aperiodic turbulent to ordered equipartition fields

Abstract

It is shown that an unmagnetized nonrelativistic thermal electron-proton plasma spontaneously emits aperiodic turbulent magnetic field fluctuations of strength $|\delta B|=9\beta_eg^{1/3}W_e^{1/2}$ G, where $\beta_e$ is the normalized thermal electron temperature, $W_e$ the thermal plasma energy density and $g$ the plasma parameter. Aperiodic modes fluctuate only in space, but are not propagating. For the unmagnetized intergalactic medium, immediately after the reionization onset, the field strength from this mechanism is about $4.7\cdot 10^{-16}$ G, too weak to affect the dynamics of the plasma. The shear and/or compression of the intergalactic medium exerted by the first supernova explosions amplify these seed fields and make them anisotropic, until the magnetic restoring forces affect the gas dynamics at ordered plasma betas near unity.