Nature 481, 480–483 (2012)

The magnetic fields seen to exist in galaxies are thought to have been seeded early in their history, then amplified through dynamo or turbulent processes. In magnetohydrodynamic simulations, a favoured explanation of the seeding is by the Biermann battery process, through which currents are generated owing to the misalignment of temperature and pressure gradients. Gianluca Gregori and colleagues now have experimental evidence to support it.

At the Laboratoire pour l'Utilisation de Lasers Intenses, close to Paris, France, Gregori et al. trained intense, short-duration laser pulses on a carbon rod held inside a low-pressure chamber. They monitored the shock evolution as the hot matter first expanded ballistically and then formed a blast wave, and also measured the magnetic-field components normal and perpendicular to the shock. Their results are consistent with protogalactic simulations, and, when appropriately scaled to galactic conditions, are the first experimental verification of the Biermann battery process, proposed more than 60 years ago.