Magnetic Amplification in Cosmic Field Explained

Experimental turbulence model matches the magnetic field amplification seen within the remains of a supernova.

Small heatmap in flame shape on a multicolor blue background. — Image courtesy of National Radio Astronomy Observatory/Associated Universities Inc.

The Science

Left over from a supernova explosion in our galaxy, Cassiopeia A contains a magnetic field that is about 100 times stronger than those nearby, making the remnant a source of bright radio emissions relatively close by within our galaxy. The amplified field is due to the outer shock wave of the supernova passing through dense, stationary clumps; the interaction amplifies and maintains the magnetic field.

The Impact

The laboratory experiments and modeling simulations run on the Mira and Intrepid supercomputers at Argonne National Laboratory answer a long-held question: why is the magnetic field amplified in this case? The research confirms that the turbulence created by the supernova’s outer shock waves hitting an interstellar cloudbank is sufficient to generate and sustain a strong magnetic field.

Summary

Astrophysicists suggested as early as 1970 that the strong magnetic field in Cassiopeia A’s core could be produced by turbulence as ejected material passes through preexisting clumps of dense interstellar gas. Now, a large collaborative group reports a combination of experimental and modeling data supporting this hypothesis. Observed measurements obtained over time show the presence of both rapidly moving (5,000–9,000 km s⁻¹) and essentially stationary dense clumps of interstellar gas within the ejecta field, or the area where matter thrown off by the supernova resides. These observations led to the hypothesis that a dense stationary cloudbank present when the star exploded in a supernova led to turbulent conditions and generated the observed magnetic field. The advent of advanced physics models, developed with support from the U.S. Department of Energy, combined with the supercomputing capabilities available through DOE user facilities such as Argonne National Laboratory’s Mira, with a peak capability of 10 quadrillion calculations per second, allowed the research team to simulate conditions in interstellar space. The results showed that the supernova shock wave becomes unstable when it encounters the clumpy gas clouds, generating a vortex, and therefore magnetic fields. The discovery provides evidence that such simulations can accurately reproduce experimental data. The ability to harmonize experimental data with simulation data confirms that the proposed physics model is accurate. Now physicists will be able to use the model to isolate variables and test new hypotheses regarding plasma turbulence.

Contact

Jena Meinecke
Department of Physics, University of Oxford, Oxford, U.K.
[email protected]

Funding

The research was supported by the European Research Council under the European Community’s Seventh Framework Programme (FP7/2007-2013)/ERC grant agreements no. 256973 and 247039, LASERLAB-EUROPE grant agreement No. 284464, the U.S. Department of Energy under Contract No. B591485 to Lawrence Livermore National Laboratory, and Field Work Proposal No. 57789 to Argonne National Laboratory. Partial support from the Science and Technology Facilities Council and the Engineering and Physical Sciences Research Council of the United Kingdom (Grant No. EP/G007187/1) also is acknowledged. The U.S. DOE supported the work of R. P. Drake, C.C. Kuranz, M. J. MacDonald and W.C. Wan under grant DE-NA0001840. The Innovative and Novel Computational Impact on Theory and Experiment (INCITE) program provided computer time.

Publications

J. Meinecke, et al. “Turbulent amplification of magnetic fields in laboratory laser-produced shock waves,” Nature Physics 10, 520-524 (2014). [DOI: 10.1038/NPHYS2978]