Small scale magnetic field evolution in the first objects formed in the universe

Abstract

Large scale magnetic fields in galaxies are thought to be generated, by a mean field dynamo. In order to have generated the fields observed, the dynamo would have had to have operated for a sufficiently long period of time. However, magnetic fields of similar intensities to the one in our galaxy, are observed in high redshift galaxies, where a mean field dynamo would not have had time to produce the observed fields. MHD turbulence produces small scale magnetic fields at a faster rate than it does mean fields, which can diffuse toward larger scales. If the turbulence is helical, magnetic fields generated at small scales can become correlated over large scales. We study the evolution of magnetic field correlations in the first objects formed in the universe, due to the action of a turbulent, helical, stochastic dynamo, for redshifts 5 ≤ z ≤ 10. Ambipolar diffusion can play a significant role in this process due to the low level of ionization of the gas in the first objects. We show that for reasonable values of the parameters that characterize the turbulent plasma in the time interval considered, fields can grow to high intensities (∼ µG), with large coherence lengths (∼ 2 − 6 kpc).

The Influence of Magnetic Fields on the Thermodynamics of Primordial Star Formation

“…The impact of the additional metallicity has been discussed extensively in the literature (Bromm et al 2001;Schneider et al 2003;Omukai et al 2005;Schneider et al 2006;Jappsen et al 2007Jappsen et al , 2009aTornatore et al 2007;Clark et al 2008;Omukai et al 2008;Smith et al 2009). Conversely, both the amount of magnetic energy generated in the IGM by the first generation of stars, as well as their possible effects on the subsequent generations are still largely unexplored (but see Rees 1987;Kandus et al 2004). At low metallicity, dust cooling becomes important at high densities (Omukai et al 2005;Schneider et al 2006) and may easily dominate over the additional heating from ambipolar diffusion.…”

Origin of Magnetic Fields and the First Objects

“…Kandus, Opher and Barros [10] suggested that stochastic helical turbulence could have amplified a primordial seed magnetic field ∼ 10 −20 G up to the microgauss fields that are observed in objects at z 5. They studied a typical low ionized cloud at z ∼ 10 and examined the amplification of the magnetic field due to stochastic turbulence from z ∼ 10 to z ∼ 5.…”