Paris, 9 September 2011
Why is the gas found between galaxies or between the stars of the same galaxy magnetized? An international team of astrophysicists has put forward the first potential explanation for this phenomenon: an initially weak magnetic field could have been amplified by turbulent motions(1), like those that take place within the Earth and the Sun, and which must have existed in the primordial universe. "According to our simulations, this turbulence produced an exponential growth of the magnetic field," explain research leaders Christoph Federrath and Gilles Chabrier. "Our calculations show that this phenomenon is possible even under extreme physical conditions, such as those encountered shortly after the Big Bang, when the first stars formed."
Their 3D digital simulations reveal how magnetic field lines can be drawn out, twisted and folded by turbulent "flows." Just as electricity generates a magnetic field through the movement of charged particles, the charges themselves are subjected to a force as they move through a magnetic field. According to the astrophysicists, "The interaction between a magnetic field and turbulent energy — a kind of kinetic energy generated by turbulence — can amplify an initially weak field, converting it into a strong field." The researchers hope that their work will shed light on the properties of the very first stars and galaxies to form in the universe.
This research is part of a scientific project headed by Gilles Chabrier, 2006 CNRS Silver Medal laureate, and funded by a European Research Council advanced grant under the auspices of the 7th Framework Program devoted to the understanding of the physics of protostars and extrasolar planets.
© © Federrath, Chabrier, Schober, Banerjee, Klessen, and Schleicher
Turbulent structures of the magnetic field in four digital models representing significantly different physical conditions. For example, the interior of the Sun (top left) is not highly compressible and is characterized by subsonic flows, whereas the typical plasma of the primordial universe (bottom right) was very probably dominated by powerful compressive forces and highly supersonic turbulence.
1 - This motion is a "flow" that does not flow "calmly" in a laminar pattern. It is locally subjected to extreme speed variations in every direction, which creates turbulences, or vortexes. These vortexes supply the equivalent of a form of kinetic energy called turbulent energy.
Mach Number Dependence of Turbulent Magnetic Field Amplification: Solenoidal versus Compressive Flows. C. Federrath, G. Chabrier, J. Schober, R. Banerjee, R. S. Klessen, and D. R. G. Schleicher. Physical Review Letters. 9 September 2011.
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