|
Aktuelle
Meldungen bei MM-Physik |
|
Aktuelle
Meldungen bei MM-Physik |
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. |
