Magnetic Fields Sculpt Narrow Jets From Dying Star

Mar 02, 2006
Magnetic Fields Sculpt Narrow Jets From Dying Star
Artist's Conception Shows Tightly-Wound Magnetic Field Confining Jet, Credit: NRAO/AUI/NSF

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 2 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.

Source: National Radio Astronomy Observatory

Explore further: NASA telescopes set limits on space-time quantum 'foam'

Related Stories

Video: Kepler observes Neptune dance with its moons

May 15, 2015

NASA's Kepler spacecraft, known for its planet-hunting prowess of other stars, is also studying solar system objects. In its new K2 mission, Neptune and two of its moons, Triton and Nereid, have been imaged. ...

An improved model for star formation

May 08, 2015

Star formation, once thought to consist essentially of just the simple coalescence of material by gravity, actually occurs in a complex series of stages. As the gas and dust in giant molecular clouds come ...

Glitter cloud may serve as space mirror

Apr 16, 2015

What does glitter have to do with finding stars and planets outside our solar system? Space telescopes may one day make use of glitter-like materials to help take images of new worlds, according to researchers ...

Recommended for you

Dawn spirals closer to Ceres, returns a new view

11 hours ago

A new view of Ceres, taken by NASA's Dawn spacecraft on May 23, shows finer detail is becoming visible on the dwarf planet. The spacecraft snapped the image at a distance of 3,200 miles (5,100 kilometers) ...

NASA telescopes set limits on space-time quantum 'foam'

17 hours ago

A team of scientists has used X-ray and gamma-ray observations of some of the most distant objects in the universe to better understand the nature of space and time. Their results set limits on the quantum ...

Shining message about the end of the Dark Ages

19 hours ago

An international team, including researchers from the Centre for Astronomy of Heidelberg University (ZAH), has discovered three "cosmic Methusalems" from the earliest years of the universe. These unusual stars are about 13 ...

The kinematics of merging galaxies

19 hours ago

The unprecedented sensitivity of space telescopes has powered a revolution over the past decade in our understanding of galaxies in the young universe during its first billion years of existence. These primitive ...

User comments : 0

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.