Media Contact:
Emily Donahue, Public Information Officer
Northeastern University, Boston, Mass.
E.donahue@neu.edu
617-373-5720
Science Contact:
Luis Anchordoqui
Physics Department, NU, Boston, Mass.
L.anchordoqui@neu.edu
617-373-2902
February 13, 2003
Boston, Mass. -- Neutron stars, long revered as physics laboratories in space because of the insights they provide into the nature of matter and energy, may be sources of neutrinos, exotic elementary particles that rarely interact with other matter. One South Pole neutrino catcher called IceCube may be the first to detect these neutron star neutrinos, according to a team led by Luis Anchordoqui of Northeastern University in Boston.
Neutron stars are the virtually invisible, 10-mile-wide core remains of a once massive star, often residing in binary star systems. Penetrating neutrinos could provide valuable, new information about how neutron stars evolve, because they can plow through the dust and gas surrounding the commotion of neutron star activity that often blocks light, Anchordoqui said.
"Neutrinos can offer brand new information about how neutron stars work," said Anchordoqui. "Neutrinos from the Sun confirmed the theory of nuclear fusion, a discovery recognized this past year by the Nobel Prize committee. Neutrino astronomy is in its infancy, with great results soon to come."
Anchordoqui and his colleagues discuss the expected neutrino output from a well-studied source named A0535+26 and an Antarctic neutrino detector IceCube in the upcoming May 20, 2003, edition of the Astrophysical Journal. Co-authors include Diego Torres of Lawrence Livermore National Laboratory, Thomas McCauley of Northeastern, Gustavo Romero of Instituto Argentino de Radioastronomia, and Felix Aharonian of Max Planck Institut fuer Kernphysik.
Neutrinos are elementary particles similar to electrons but with no electrical charge and very little mass. Neutrinos hardly interact with matter and could pass through billions of miles of lead untouched. Thus, neutrinos are hard to detect yet plump with information about their source.
A neutron star is the core remains of a star at least eight times as massive as the Sun. After exhausting its nuclear fuel, such a star blows off much of its mass, an event called a supernova. The core, still containing about the mass of the Sun, collapses to a sphere no wider than Boston.
Although they are but tiny chunks located thousands of light years from Earth, neutron stars are often visible when residing in binary star 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, called accretion, is a turbulent event that shines brightly. Some neutron stars cannibalize gas from their companions and often devour them completely over the course of millions of years.
Neutrinos are produced by protons (hydrogen gas stripped of electrons) whipped to velocities close to light speed by the neutron star magnetic field, according to the new calculations. The magnetic field is 10^12 (a trillion) times stronger than our Sun's field. While gas and dust block much of the light from exiting this scene, shielding our view of the details of the binary system, neutrinos escape largely unscathed.
Diego Torres said that an Antarctic neutrino detector called IceCube, now under construction, could observe how an accretion disk in A0535+26 periodically forms and disappears as the two stars orbit each other. IceCube is an international, cubic-kilometer neutrino detector built in the clear, deep ice of the South Pole. IceCube attempts to catch neutrinos as they enter and pass entirely through the Earth from the North Pole.
"The neutrinos from A0535+26 would overwhelm those from any other neutron star system we know," Torres said. "A0535+26 is also a periodic source, and it just may be the brightest observable source of sub-TeV-energy neutrinos. Someday in the near future, we could do multi-wavelength-particle astronomy and reconstruct the formation and loss of the accretion disc by combining observations in X rays, gamma rays, and neutrinos."
Furthermore, detection of neutrinos automatically implies that the origin of high-energy radiation is hadronic in nature (protons accelerated up to hundreds of TeVs.)
The team suggests that the A0535+26 could be just the tip of the iceberg for IceCube. Neutrinos might also be produced inside a neutron star core. Detection of this type of neutrino would be tantamount to sampling matter in a neutron star, a paramount achievement that would at long last reveal the nature of the neutron star interior and the physics of matter under extreme gravity.
A neutrino from the core of A0535+26's neutron star would be coming from the same direction yet of a different energy, thus distinguishable from other neutrinos.
The team's upcoming journal article is now available on line at http://mentor.lanl.gov/abs/hep-ph/0211231. For more information and images of the IceCube detector, refer to http://icecube.wisc.edu/.