Generation of scaled protogalactic seed magnetic fields in laser-produced shock waves

Abstract

The standard model for the origin of galactic magnetic fields is through the amplification of seed fields via dynamo or turbulent processes to the level consistent with present observations. Although other mechanisms may also operate, currents from misaligned pressure and temperature gradients (the Biermann battery process) inevitably accompany the formation of galaxies in the absence of a primordial field. Driven by geometrical asymmetries in shocks associated with the collapse of protogalactic structures, the Biermann battery is believed to generate tiny seed fields to a level of about 10(-21) gauss (refs 7, 8). With the advent of high-power laser systems in the past two decades, a new area of research has opened in which, using simple scaling relations, astrophysical environments can effectively be reproduced in the laboratory. Here we report the results of an experiment that produced seed magnetic fields by the Biermann battery effect. We show that these results can be scaled to the intergalactic medium, where turbulence, acting on timescales of around 700 million years, can amplify the seed fields sufficiently to affect galaxy evolution.

Time evolution and asymmetry of a laser produced blast wave

“…Similar dynamics causing two shocks to be produced in an interaction have been observed by Tzeferacos et al 18 and Gregori et al 7 In the former, two fronts are observed in FLASH simulations and one is suggested to be due a shock launched into the background gas and the second from the target material expanding behind. In the latter reference, the B-dot probe signal showed measurements of two peaks in the magnetic field strengths, and this is postulated to be from the target ejecta material.…”

“…2 Such shock waves, known as blast waves, are common in astrophysics, and blast wave dynamics are used to predict supernova remnant evolution. 3,4 These disturbances and associated shocks are readily created with high energy, intense lasers, enabling a detailed laboratory study of astrophysical relevant topics such as shock driven radiative instabilities, 5 secondary shock formation, 6 and the seeding 7 and amplification 8 of galactic magnetic fields. Furthermore, the scale-invariance of blast waves and application of ideal magneto-hydrodynamics to experiment 9 enable direct comparison of small scale (mmsized and sub-micro-second) laboratory experiments with astronomical systems which have spatiotemporal scales many orders of magnitude larger.…”

Turbulent amplification of magnetic fields in laboratory laser-produced shock waves

“…1) of the magnetic field is 2-3 times larger than without it. Previous results 22 have indicated that perpendicular magnetic fields are produced at the shock front through the Biermann battery mechanism 23 owing to misaligned pressure and density gradients. We find that for shocks passing through a grid, magnetic field amplification continues to occur long after the shock has passed, suggesting that an alternative mechanism is at play.…”

“…The interferometer was of Mach-Zehnder type with ∼50 mm field of view, and was used to provide the electron density. The induction coils are based on a modified design 22,29 to achieve ∼100 MHz bandwidth. They are placed at 3 cm (and at 4 cm for some laser shots) from the carbon rod position (that is, the centre of the initial blast).…”

Fully kinetic Biermann battery and associated generation of pressure anisotropy

“…Both the seed field required for the generation of astrophysical magnetic fields [1,2] and intense magnetic fields generated in laser-solid interaction laboratory experiments [3][4][5][6] have been attributed to the Biermann battery [7]. The Biermann battery mechanism generates magnetic fields due to nonparallel temperature and density gradients.…”