Washington, Jan 10 : Astronomers have traced the source of a mysterious giant cloud of antimatter surrounding the galactic center of the Milky Way galaxy, to binary star systems.
The discovery took four years of observations from the European Space Agency's Integral (International Gamma-Ray Astrophysics Laboratory) satellite.
What the satellite found was that the cloud of antimatter extends farther on the western side of the galactic center than it does on the eastern side.
This imbalance matches the distribution of a population of binary star systems that contain black holes or neutron stars, strongly suggesting that these binaries are churning out at least half of the antimatter, and perhaps all of it.
The antimatter is probably produced in a region near the neutron stars and black holes, where powerful magnetic fields launch jets of particles that rip through space at near-light speed.
After the antimatter cloud was discovered in the 1970s by gamma-ray detectors flown on balloons, scientists proposed a wide range of explanations for its origin, as such a phenomenon is exceedingly rare in the cosmos.
For years, many theories centered around radioactive elements produced in supernovae, prodigious stellar explosions. Others suggested that the positrons come from neutron stars, novae, or colliding stellar winds.
But, Integral found that certain types of binary systems near the galactic center are also skewed to the west. These systems are known as hard low-mass X-ray binaries, since they light up in high-energy (hard) X-rays as gas from a low-mass star spirals into a companion black hole or neutron star.
Because the two "pictures" of antimatter and hard low-mass X-ray binaries line up, it strongly suggests that the binaries are producing significant amounts of positrons.
"Simple estimates suggest that about half and possibly all the antimatter is coming from X-ray binaries," said Georg Weidenspointer of the Max Planck Institute for Extraterrestrial Physics in Germany.
"The reported Integral detection of an asymmetry represents a significant step forward toward a solution of one of the major outstanding problems in high-energy astrophysics. I think I can hear a collective sigh of relief emanating from the community," said Marvin Leventhal, a University of Maryland professor emeritus.