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Ancient Galactic Magnetic Fields Stronger than Expected (Forwarded)



 
 
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Old August 11th 08, 12:13 AM posted to sci.space.news
Andrew Yee[_1_]
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Default Ancient Galactic Magnetic Fields Stronger than Expected (Forwarded)

Public Affairs Office
Los Alamos National Laboratory

Contact:
John C. Cannon, jcannon @ lanl.gov

July 23, 2008

Ancient Galactic Magnetic Fields Stronger than Expected

LOS ALAMOS, N.M. -- Mining the far reaches of the universe for clues about
its past, a team of scientists including Philipp Kronberg of Los Alamos
National Laboratory has proposed that magnetic fields of ancient galaxies
like ours were just as strong as those existing today, prompting a
rethinking of how our galaxy and others may have formed.

With powerful telescopes and sophisticated measurements, the team probed
back in time to see the ancient universe as it existed some 8 to 9 billion
years ago. Their research was published in the July 17 edition of Nature.

Until now, a prevailing view in the astrophysical community has been that
galactic magnetic fields gradually increased over cosmic time up to their
present strengths and that in the nascent universe, magnetic fields were
initially very weak. Astrophysicists explain this gradual growth of
magnetism over time with the large-scale "galactic dynamo" model.

The letter in the current issue of Nature extends a parallel, larger study
by Kronberg et al. of early magnetic fields from the March 2008 edition of
The Astrophysical Journal. That study, whose contributors also included LANL
colleagues David Higdon and Margaret Short, relied mostly on Faraday
rotation measures (RM) taken at radio wavelengths, beyond what is visible to
the human eye.

By measuring how far the radio waves were pulled toward the red end of the
spectrum -- known as "redshift" -- Kronberg and his colleagues homed in on
the location of magnetic fields in the distant universe.

What allowed the team to take a more detailed look at the ancient universe
in this Nature letter was the addition of high-resolution optical spectra by
Martin Bernet, Francesco Miniati, and Simon Lilly at the ETH Zich (the Swiss
Federal Institute of Technology) from the European Southern Observatory's
8-meter telescope, located in Chile's Atacama Desert. Their measurements at
optical wavelengths of more than 70 quasars were combined with the RM data
Kronberg has been collecting for more than 25 years -- data based on
accurate radio RM measurements from several of the world's most powerful
radio telescopes, including the Very Large Array near Soccoro, New Mexico,
and the 100-meter dish in Effelsberg, Germany.

"It was thought that, looking back in the past, earlier galaxies would not
have generated much magnetic field," Kronberg said. "The results of this
study show that the magnetic fields within Milky Way-like galaxies have been
every bit as strong over the last two-thirds of the Universe's age as they
are now -- and possibly even stronger then."

Serving as a looking glass into the past, the powerful telescope at the
European Southern Observatory, adding to the radio RM data, allowed the
scientists to make observations of high magnetic fields between 8 billion
and 9 billion years ago for 70 intervening galaxies whose faint optical
absorption spectra revealed them as "normal" galaxies. That means that
several billion years before the existence of our own sun, and within only a
few billion years of the Big Bang, ancient galaxies were exerting the tug of
these strong magnetic fields.

This research suggests that the magnetic fields in galaxies did not arise
due to a slow, large-scale dynamo effect, which would have taken 5 billion
to 10 billion years to reach their current measured levels. "There must be
some other explanation for a much quicker and earlier amplification of
galactic magnetic fields," Kronberg said. "From the time when the first
stars and galaxies formed, their magnetic fields have probably have been
amplified by very fast dynamos. One good possibility is that it happened in
the explosive outflows that were driven by supernovae, and possibly even
black holes in the very earliest generations of galaxies."

This realization brings a new focus on the broader question of how galaxies
form. Instead of the commonly held view that magnetic fields have little
relevance to the genesis of new galaxies, it now appears that they are
indeed important players. If so, strong magnetic fields a long time ago are
one of the essential ingredients that explain the very existence of our
galaxy and others like it.

Los Alamos National Laboratory is a multidisciplinary research institution
engaged in strategic science on behalf of national security. The Laboratory
is operated by a team composed of Bechtel National, the University of
California, BWX Technologies, and Washington Group International for the
Department of Energy's National Nuclear Security Administration.

Los Alamos enhances national security by ensuring the safety and reliability
of the U.S. nuclear stockpile, developing technologies to reduce threats
from weapons of mass destruction, and solving problems related to energy,
environment, infrastructure, health and global security concerns.
 




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