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Topflight astrophysics boffins believe they may have cracked the tricky problem of how to make antimatter, which would be useful for many purposes: for instance powering relatively practical starships, or - of course - blowing up an entire planet in one go. However, it appears that making antimatter requires the possession of a black hole or a neutron star, so it won't be happening any time soon.

For those few readers who don't know, antimatter is like normal matter but with properties reversed. Thus a normal electron of the type used to publish this article has a negative charge*, but an anti-electron (aka positron) is positive.

The energy created when electrons and positrons meet is emitted in the form of gamma rays. Back in the 1970s the existence of antimatter in the universe was verified in the obvious way - by sending gamma-ray detectors into the upper atmosphere on balloons.

According to the balloon detectors, there seems to be a large cloud of positrons throughout the centre of our galaxy, about 10,000 lightyears across and giving off the energy of 10,000 suns from constant antimatter annihilation as it reacts with ordinary electrons. But nobody knew why or how the antimatter was being created in the first place.

Now, however, that conundrum seems to have been solved.

"I think I can hear a collective sigh of relief," said Marvin Leventhal, a noted brainbox active in the field.

It seems that an international team of astrophysicists boiled down four years' worth of data from the European Space Agency (ESA) satellite INTEGRAL (INTErnational Gamma Ray Astrophysics Laboratory). They noted that the glowing gamma-ray positron cloud bulged significantly in the direction of Galactic west.

The positron cloud bulge coincided with a region in which there are believed to be a lot of binary star systems containing neutron stars or the even more outrageous black holes. These star systems are known as "hard low-mass X-ray binaries".

According to NASA, this strongly suggests that "these binaries are churning out at least half of the antimatter, and perhaps all of it."

Rival boffins had of late been suggesting that the antimatter was actually created by some process involving dark matter, but NASA's Gerry Skinner pooh-poohed such notions.

"The INTEGRAL results seem to rule out dark matter," he said.

"Simple estimates suggest that about half and possibly all the antimatter is coming from X-ray binaries," added his colleague Georg Weidenspointer of Germany's Max Planck Institute for Extraterrestrial Physics.

Weidenspointer, Skinner and Leventhal published their findings in the current issue of Nature.

Nobody knows exactly how black holes and neutron stars make antimatter, however. Nor is it clear how the antimatter gets away from such massive gravity fields, to drift about the Galactic core getting annihilated.

"We expected something unexpected, but we did not expect this," said Skinner, rather splendidly, suggesting that nobody could have expected so much unexpectedness.

NASA presumes to trump INTEGRAL by launching GLAST, the Gamma-ray Large Area Space Telescope, this year. The space agency says its new satellite "may help clarify" the business of antimatter production; also that it might allow the detection of other, larger antiparticles rather than just positrons. ®

*Possibly explains a lot from a literary viewpoint.

What you need to know about cloud backup