Andrew Yee
March 1st 06, 08:59 PM
National Radio Astronomy Observatory
P.O. Box O
Socorro, NM 87801
http://www.nrao.edu
Contact:
Dave Finley, Public Information Officer
(505) 835-7302
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
P.O. Box O
Socorro, NM 87801
http://www.nrao.edu
Contact:
Dave Finley, Public Information Officer
(505) 835-7302
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