NEW CHANDRA MOVIE FEATURES NEUTRON STAR ACTION
WASHINGTON -- Unlike with some blockbuster films, the sequel to a
movie from NASA's Chandra X-ray Observatory is better than the first.
This latest movie features a deeper look at a fast moving jet of
particles produced by a rapidly rotating neutron star, and may
provide new insight into the nature of some of the densest matter in
the universe.
The hero of this Chandra movie is the Vela pulsar, a neutron star that
was formed when a massive star collapsed. The Vela pulsar is about
1,000 light-years from Earth, about 12 miles in diameter, and makes a
complete rotation in 89 milliseconds, faster than a helicopter rotor.
As the pulsar whips around, it spews out a jet of charged particles
that race along the pulsar's rotation axis at about 70 percent of the
speed of light. The new Chandra data, which were obtained from June
to September 2010, suggest the pulsar may be slowly wobbling, or
precessing, as it spins. The period of the precession, which is
analogous to the slow wobble of a spinning top, is estimated to be
about 120 days.
"We think the Vela pulsar is like a rotating garden sprinkler --
except with the water blasting out at over half the speed of light,"
said Martin Durant of the University of Toronto in Canada, who is the
first author of the paper describing these results.
One possible cause of precession for a spinning neutron star is it has
become slightly distorted and is no longer a perfect sphere. This
distortion might be caused by the combined action of the fast
rotation and "glitches," sudden increases of the pulsar's rotational
speed due to the interaction of the superfluid core of the neutron
star with its crust.
"The deviation from a perfect sphere may only be equivalent to about
one part in 100 million," said co-author Oleg Kargaltsev of The
George Washington University in Washington, who presented these
results Monday at the 221st American Astronomical Society meeting in
Long Beach, Calif. "Neutron stars are so dense that even a tiny
distortion like this would have a big effect."
If the evidence for precession of the Vela pulsar is confirmed, it
would be the first time a neutron star has been found to be this way.
The shape and the motion of the Vela jet look strikingly like a
rotating helix, a shape that is naturally explained by precession.
Another possibility is the strong magnetic fields around the pulsar
are influencing the shape of the jet. For example, if the jet
develops a small bend caused, by precession, the magnetic field's
lines on the inside of the bend will become more closely spaced. This
pushes particles toward the outside of the bend, increasing the
effect.
"It's like having an unsecured fire hose and a flow of water at high
pressure," said co-author George Pavlov, principal investigator of
the Chandra proposal at Pennsylvania State University in University
Park. "All you need is a small bend in the hose and violent motion
can result."
This is the second Chandra movie of the Vela pulsar. The original was
released in 2003 by Pavlov and co-authors. The first Vela movie
contained shorter, unevenly spaced observations so that the changes
in the jet were less pronounced and the researchers did not argue
that precession was occurring. However, based on the same data,
Avinash Deshpande of Arecibo Observatory in Puerto Rico and the Raman
Research Institute in Bangalore, India, and the late Venkatraman
Radhakrishnan, argued in a 2007 paper the Vela pulsar might be
precessing.
Astronomers have returned to observing Vela because it offers an
excellent chance to study how a pulsar and its jet work. The 0.7
light-year-long jet in Vela is similar to those produced by accreting
supermassive black holes in other galaxies, but on a much smaller
scale. Because Vela's jet changes dramatically over a period of
months and is relatively close, it can be studied in great detail
unlike jets from black holes that change over much longer timescales.
If precession is confirmed and the Vela pulsar is indeed a distorted
neutron star, it should be a persistent source of gravitational
waves, and would be a prime target for the next generation of
gravitational wave detectors designed to test Einstein's theory of
general relativity.
A paper describing these results will be published in Thursday's The
Astrophysical Journal. Other co-authors of the paper were Julia
Kropotina and Kseniya Levenfish from St. Petersburg State
Polytechnical University in St. Petersburg, Russia.
NASA's Marshall Space Flight Center in Huntsville, Ala., manages the
Chandra program for NASA's Science Mission Directorate in Washington.
The Smithsonian Astrophysical Observatory controls Chandra's science
and flight operations from Cambridge, Mass.
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