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Laser Hints at Magnetism’s Origins

Photonics.com
Feb 2012
OXFORD, England, Feb. 1, 2012 — Using a high-power laser to simulate the conditions under which the first galaxies formed, scientists may have uncovered a clue as to how magnetism originated in the universe.

Magnetic fields exist throughout galactic and intergalactic space and in the stars and planets. The magnetic fields in our solar system shield us from the harmful effects of cosmic rays, allowing life to thrive. What is puzzling, however, is how they originated. A method for creating magnetic fields without a magnet has long been theorized, but until now, the process had not been demonstrated.


On the left, an image of a laser-produced shock wave. Brighter colors correspond to regions of higher density or temperature. On the right, a simulation of a collapsing shock wave arising during the pregalactic phase. [Image: (left) A. Ravasio and A. Pelka (LULI), and J. Meinecke and C. Murphy (Oxford). (right) F. Miniati (ETH).]

Now, researchers from Oxford University have used a high-power laser to create magnetic fields similar to those thought to be involved in the formation of the very first galaxies. During the experiment, the scientists used the laser to explode a rod of carbon, similar to pencil lead, in helium gas. The detonation was designed to mimic the cauldron of plasma — ionized gas containing free electrons and positive ions — out of which the first galaxies formed. It was designed to prove a theory, known as the “Biermann battery effect,” describing how magnetic fields could form where previously none had existed.

The team discovered within a microsecond of the explosion strong electron currents and magnetic fields formed around a shock wave. They took these results and compared them to existing planetary data. Using computational resources from STFC’s e-science department, they scaled the results through 22 orders of magnitude and found that their measurements closely matched “magnetic seeds” #8212; tiny magnetic fields — predicted by theoretical studies of galaxy formation. These fields can be amplified by turbulent motions and can strongly affect the evolution of the galactic medium.

“Our experiment recreates what was happening in the early universe and shows how galactic magnetic fields might have first appeared,” said Dr. Gianluca Gregori of Oxford University. “It opens up the exciting prospect that we will be able to explore the physics of the cosmos, stretching back billions of years, in a laser laboratory here on Earth.”

The experiments were conducted at the Laboratoire pour l’Utilisation de Lasers Intenses laser facility in France. The team included scientists from Oxford University, Rutherford Appleton Laboratory, Laboratoire pour l’Utilisation de Lasers Intenses, University of Strathclyde, University of California Los Angeles, University of Michigan, University of York, Osaka University, Lawrence Livermore National Laboratory, ETH-Zurich.

The findings were published in the Jan. 25 issue of Nature.

For more information, visit: www.ox.ac.uk


GLOSSARY
shock wave
Interruption in the normal flow of a plasma or fluid characterized by sharp rises in velocity, temperature and pressure. As the shock passes into a gaseous compound, gas particles are heated and accelerated.
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