origin of antimatter surrounding the galactic center

New research based on the four years of observations from the European Space Agency’s Integral (INTErnational Gamma-Ray Astrophysics Laboratory) satellite may have cleared up one of the most vexing mysteries in our Milky Way: the origin of a giant cloud of antimatter surrounding the galactic center.
Integral found that the cloud 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 cloud itself is roughly 10,000 light-years across, and generates the energy of about 10,000 Suns. The cloud shines brightly in gamma rays due to a reaction governed by Einstein’s famous equation E=mc^2. Negatively charged subatomic particles known as electrons collide with their antimatter counterparts, positively charged positrons. When electrons and positrons meet, they can annihilate one another and convert all of their mass into gamma rays with energies of 511,000 electron-volts (511 keV). The antimatter cloud was discovered in the 1970s by gamma-ray detectors flown on balloons. Scientists have proposed a wide range of explanations for the origin of the antimatter, which 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.
In recent years, some theorists championed the idea that particles of dark matter were annihilating one another, or with atomic matter, producing electrons and positrons that annihilate into 511-keV gamma rays. But other scientists remained skeptical, noting that the dark matter particles had to be significantly lighter than most theories predicted.

Integral found 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 strongly suggests the binaries are producing significant amounts of positrons.NASA’s Gamma-ray Large Area Space Telescope (GLAST), scheduled to launch in 2008, may help clarify how objects such as black holes launch particle jets. Conceivably, it could even detect higher-energy gamma rays from heavier types of dark matter particles annihilating one another.