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EMBARGOED For Release: 1:00 p.m. EST, March 1, 2006

Magnetic Fields Sculpt Narrow Jets From Dying Star

Molecules spewed outward from a dying star are confined into narrow jets
by a tightly-wound magnetic field, according to astronomers who used the
National Science Foundation's Very Long Baseline Array (VLBA) radio
telescope to study an old star about 8,500 light-years from Earth.

The star, called W43A, in the constellation Aquila, is in the process of
forming a planetary nebula, a shell of brightly-glowing gas lit by the
hot ember into which the star will collapse. In 2002, astronomers
discovered that the aging star was ejecting twin jets of water
molecules. That discovery was a breakthrough in understanding how many
planetary nebulae are formed into elongated shapes.

"The next question was, what is keeping this outpouring of material
confined into narrow jets? Theoreticians suspected magnetic fields, and
we now have found the first direct evidence that a magnetic field is
confining such a jet," said Wouter Vlemmings, a Marie Curie Fellow
working at the Jodrell Bank Observatory of the University of Manchester
in England.

"Magnetic fields previously have been detected in jets emitted by
quasars and protostars, but the evidence was not conclusive that the
magnetic fields were actually confining the jets. These new VLBA
observations now make that direct connection for the very first time,"
Vlemmings added.

By using the VLBA to study the alignment, or polarization, of radio
waves emitted by water molecules in the jets, the scientists were able
to determine the strength and orientation of the magnetic field
surrounding the jets.

"Our observations support recent theoretical models in which
magnetically-confined jets produce the sometimes-complex shapes we see
in planetary nebulae," said Philip Diamond, also of Jodrell Bank
Observatory.

During their "normal" lives, stars similar to our Sun are powered by the
nuclear fusion of hydrogen atoms in their cores. As they near the end of
their lives they begin to blow off their outer atmospheres and
eventually collapse down to a white dwarf star about the size of Earth.
Intense ultraviolet radiation from the white dwarf causes the gas thrown
off earlier to glow, producing a planetary nebula. Astronomers believe
that W43A is in the transition phase that will produce a planetary
nebula. That transition phase, they say, is probably only a few decades
old, so W43A offers the astronomers a rare opportunity to watch the process.

While the stars that produce planetary nebulae are spherical, most of
the nebulae themselves are not. Instead, they show complex shapes, many
elongated. The earlier discovery of jets in W43A showed one mechanism
that could produce the elongated shapes. The latest observations will
help scientists understand the mechanisms producing the jets.

The water molecules the scientists observed are in regions nearly 100
billion miles from the old star, where they are amplifying, or
strengthening, radio waves at a frequency of 22 GHz. Such regions are
called masers, because they amplify microwave radiation the same way a
laser amplifies light radiation.

The earlier observations showed that the jets are coming out from the
star in a corkscrew shape, indicating that whatever is squirting them
out is slowly rotating.

Vlemmings and Diamond worked with Hiroshi Imai of Kagoshima University
in Japan. The astronomers reported their work in the March 2nd issue of
the scientific journal Nature.

The VLBA is a system of ten radio-telescope antennas, each with a dish
25 meters (82 feet) in diameter and weighing 240 tons. From Mauna Kea on
the Big Island of Hawaii to St. Croix in the U.S. Virgin Islands, the
VLBA spans more than 5,000 miles, providing astronomers with the
sharpest vision of any telescope on Earth or in space. Dedicated in
1993, the VLBA has an ability to see fine detail equivalent to being
able to stand in New York and read a newspaper in Los Angeles.

The National Radio Astronomy Observatory is a facility of the National
Science Foundation, operated under cooperative agreement by Associated
Universities, Inc.

IMAGE CAPTION:
[http://www.nrao.edu/pr/2006/magneticjet/magneticjet.jpg (145KB)]
Artist's Conception Shows Tightly-Wound Magnetic Field Confining Jet.
CREDIT: NRAO/AUI/NSF