Bring matter and anti-matter together, and you get a potent explosion. Since antimatter is annihilated almost as soon as it forms, you wouldn’t think you could find any out there in the Universe. But you’d be wrong. There’s a giant cloud of the anti-stuff in the central regions of the Milky Way. Oh, and the cloud is lopsided.



An international team of astronomers have gathered together 4 years of observations from ESA’s Integral space observatory. The gamma ray observatory is able to detect the telltale burst of radiation when a particle of antimatter meets its normal matter counterpart. The two particles annihilate each other in a powerful blast of gamma rays.

This burst of radiation is very specific; the gamma rays from a matter/antimatter annihilation carry exactly 511 thousand electron-volts of energy. So the astronomers just used Integral to scan the skies looking for these 511 keV emissions.

So where does all this antimatter come from? Astronomers think that exploding stars could produce it during stellar outbursts. But they’re not sure if this antimatter could actually be released in significant quantities to explain the large cloud near the centre of the galaxy.

Perhaps there’s a more exotic process going on. Other astronomers have theorized that the shape and position of the antimatter cloud matches the expected distribution of dark matter in the centre of the galaxy. Perhaps dark matter is somehow being annihilated or decaying into other particles – including antimatter.

The new results from Integral actually point away from this theory. The antimatter cloud is lopsided, with twice as much material on one side of the galaxy as the other. Astronomers would expect that the antimatter should match the distribution of the dark matter.

There’s one last explanation. Theorists have proposed that a certain kind of binary star system, where an exotic compact object, like a white dwarf, neutron star or black hole, is a gravitational dance with a regular star. The exotic star siphons away material, which piles up on its surface. In this extreme environment, antimatter could be spontaneously generated in the intense radiation field.

Integral found a large population of binary stars located off-centre in the galaxy, corresponding to the distribution of the antimatter. So instead of a cloud of antimatter, there’s just a diffuse glow of gamma rays coming from all these binary star systems.

Original Source: ESA News Release