Researchers at the University of Rochester have uncovered how giant magnetic fields up to a billion, billion miles across, such as the one that envelopes our galaxy, are able to take shape despite a mystery that suggested they should collapse almost before theyd begun to form. Astrophysicists have long believed that as these large magnetic fields grow, opposing small-scale fields should grow more quickly, thwarting the evolution of any giant magnetic field. The team discovered instead that the simple motion of gas can fight against those small-scale fields long enough for the large fields to form. The results are published in a recent issue of Physical Review Letters.
"Understanding exactly how these large-scale fields form has been a problem for astrophysicists for a long time," says Eric Blackman, assistant professor of physics and astronomy. "For almost 50 years the standard approaches have been plagued by a fundamental mystery that we have now resolved."
The mechanism, called a dynamo, that creates the large-scale field twists up the magnetic field lines as if they were elastic ribbons embedded in the sun, galaxy or other celestial object. Turbulence kicked up by shifting gas, supernovae, or nearly any kind of random movement of matter, combined with the fact that the star or galaxy is spinning carries these ribbons outward toward the edges. As they expand outward they slow like a spinning skater extending her arms and the resulting speed difference causes the ribbons to twist up into a large helix, creating the overall orderly structure of the field.
Jonathan Sherwood | EurekAlert!
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