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News and Public Affairs
Lawrence Livermore National Laboratory

Contact: Anne Stark
Phone: (925) 422-9799
E-mail: stark8{at}llnl.gov

FOR IMMEDIATE RELEASE: March 7, 2003

NR-03-03-01

Laboratory Astrophysicist Discovers 
New Source of High-Energy Neutrinos
===================================

LIVERMORE, Calif. -- A Lawrence Livermore National Laboratory 
astrophysicist, working with an international group of researchers, 
has discovered that high-energy neutrinos -- particles that rarely 
interact with other matter -- are produced in the accretion discs of 
neutron stars in amounts significant enough to be detected by the 
next-generation of neutrino telescopes.

Using computer simulations, the team of scientists, which includes Lab 
astrophysicist Diego Torres, has shown that magnetized, accreting 
neutron stars can be a significant new source for high-energy 
neutrinos. Neutrinos are thought to be the final outcome of a chain of 
reactions initiated by proton (hydrogen atoms devoid of electrons)
collisions between matter sitting in the accretion disc and particles 
accelerated in the pulsar magnetosphere.

A neutron star is a compact object, one possible end-point of the 
evolution of a massive star. They are often in binary star systems. In 
such systems, the stars' orbit periodically brings them closer 
together to a point where the strong gravity from the neutron star can 
steal gas from the companion. The transfer of gas onto the neutron 
star (accretion) is a turbulent event that shines brightly.

Torres and his colleagues observed that during the 110-day orbital 
period of A0545+26 -- a nearby and well-studied X-ray binary -- 
high-energy neutrinos can be produced during approximately 50 days of 
that cycle in fluxes that are above and beyond the background noise of 
neutrinos expected at Earth. A0535+26 would then appear as a periodic 
source of high-energy neutrinos, Torres said.

"This is the first time we've shown that accreting X-ray binaries can 
be a periodic neutrino source that can be detected by the 
next-generation telescopes," said Torres, who works at the Lab's 
Institute of  Geophysics and Planetary Physics Torres along with 
scientists from Northeastern University, Instituto Argentino de
Radioastronomia and the Max Planck Institut fur Kernphysik will 
present their research in the upcoming May 20 edition of the 
Astrophysical Journal.

Neutron stars have long been viewed as physics laboratories in space 
because they provide insights into the nature of matter and energy. 
Torres and his colleagues believe that astronomers will be able to use 
IceCube -- a one-cubic-kilometer international high-energy neutrino 
observatory being built and installed in the deep ice below the South 
Pole -- to detect the neutron star neutrinos.

"IceCube could show how an accretion disc in A0545+26 periodically 
forms and disappears as the two tars orbit each other," Torres said. 
"The neutrinos from this disc would overwhelm those from any other 
neutron star system we know."

The team suggests that studying the A0545+26 disc is just the 
beginning of multiparticle astronomy, where photons in all wavelengths 
and neutrinos are detected at the same time.

The upcoming journal article is now available at
     http://mentor.lanl.gov/abs/hep-ph/0211231

For images of IceCube, go to http://icecube.wisc.edu

Founded in 1952, Lawrence Livermore National Laboratory is a national 
security laboratory, with a mission to ensure national security and 
apply science and technology to the important issues of our time. 
Lawrence Livermore National Laboratory is managed by the University of
California for the U.S. Department of Energy's National Nuclear 
Security Administration.

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