The generation of strong magnetic fields during the formation of the first stars

The ubiquity of turbulence in the primordial minihalos has been shown from cosmological hydro-dynamical simulations of primordial star formation. This has strong implications on the subsequent evolution, in particular on the generation of magnetic fields via small-scale dynamo action. Using high-resolution numerical simulations, we show that in the presence of turbulence, initial weak seed magnetic fields are exponentially amplified by the small-scale dynamo during the formation of the first stars. The field amplification due to the dynamo is shown to provide additional amplification over what is expected from pure gravitational compression of the field lines. We find that the presence of the small-scale dynamo can only be identified in numerical simulations where the turbulent motions in the central collapsing core are resolved by at least 32 grid cells. We conclude that strong magnetic fields are generated during the birth of the first stars in the universe and discuss implications for cosmic evolution.S. S thanks the German Science Foundation (DFG) for financial support via the priority program 1177 ’Witnesses of Cosmic History: Formation and evolution of black holes, galaxies and their environment’ (grant KL 1358/10). D. R. G. S is supported by the European Community’s Seventh Framework Programme (FP7/2007-2013) under grant agreement No 229517. R. B is funded by the Emmy-Noether grant (DFG) BA 3607/1. C. F and R. S. K are supported by the Landesstiftung Baden-Württemberg via their program International Collaboration II under grant PLS-SPII/18. Computing time at the Leibniz-Rechenzentrum in Garching (Germany) via grant No. h1221 and partial support from a Frontier grant of Heidelberg University funded by the German Excellence Initiative is acknowledged