Laboratory astrophysicist discovers new source of high-energy neutrinos

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 stars 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.