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5. Mai 2000 ©
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MAGNETIC FIELDS ARE EVERYWHERE
(
AIP)

MAGNETIC FIELDS ARE EVERYWHERE. The history of the universe is usually described in terms of the distribution of matter: first primordial knots, then clouds, galaxies, stars, and clusters. A parallel, and perhaps not unrelated, saga can be written for magnetic fields. Basically, Philipp Kronberg (416-978-4971) of the University of Toronto finds magnetic fields every place he has looked in the cosmos: within the Milky Way (where the fields are typically about 5 microgauss), in intergalactic areas within galaxy clusters (1-2 microgauss for the Coma cluster, 350 million light years away), and even outside clusters. The latter observations are brand new and were reported by Kronberg at the APS meeting (http://www.aps.org/meet/APR00/baps/vpr/layb7-02.html). Detecting weak magnetic fields outside clusters was difficult and required the use of new low-frequency receivers mounted on the Very Large Array (VLA) radio telescope. The radio range employed, around 75 MHZ, is normally problematic owing to scattering in the Earth's ionosphere, but new image processing techniques have allowed a sharp VLA "deep field" image to be formed. From the intensity of the radio glow, Kronberg deduced a magnetic field of about 10^-8 to 10^-7 gauss for a distant region outside any galaxy cluster, a place (near the "Great Wall") where fields had not been mapped before. Where did such fields come from? Kronberg suggests that huge shock waves, formed where two large streams of weakly magnetized gas come together, could amplify existing fields to much higher levels, as well as playing a part in the acceleration of cosmic rays. Angela Olinto (paper B7.1) of the University of Chicago (773-702-8206) discussed the idea of primordial magnetism, fields that might have existed at or shortly after the time of the big bang. Such fields, she speculated, might have come about through the development of some asymmetry (just as matter came to predominate over antimatter) in the infant universe. Early magnetism might then have influenced subsequent galaxy formation or even the distribution of matter now seen imprinted in the cosmic microwave background (CMB). She said that the surprising absence of subsidiary peaks in the CMB spectrum might be attributable to magnetic effects. This hypothesis could be addressed, Olinto said, by the Planck satellite (launch date several years from now), dedicated to mapping the CMB with unprecedented precision.
Kronberg at the APS meeting

 

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