Astronomers collide over matter of fact

When antimatter and matter meet, they annihilate each other utterly in a blaze of light. Now it seems the same can happen when American astronomers' claims reach the ears of rivals on this side of the Atlantic: after a brief burst, the two cancel each other out.

Yesterday, a team from the US space agency announced it had found a "fountain of antimatter" pouring out of the centre of our galaxy, the Milky Way.

According to the team, the "fountain" consisted of positrons, positively charged electrons, the "antiparticle" of the standard electron, which might be produced by the super massive black hole known to lurk at the galaxy's middle, 25,000 light years away. When a positron meets an electron, the two particles destroy each other and give off a burst of radiation.

"The origin of this new and unexpected source of antimatter is a mystery," said William Purcell, assistant professor of physics and astronomy at Northwestern University.

Which sounded fine; except that Sir Martyn Rees, the British Astronomer Royal, reckoned that, strictly speaking, not only was this not antimatter, it wasn't a mystery where it came from.

"I don't think it's wildly exciting," Sir Martyn said yesterday. "They haven't actually found evidence of antiprotons [the antimatter equivalent of the proton] - just positrons. They're everywhere: they can be produced by the decay of radioactive elements in the leftovers of a supernova. What they really haven't found is antimatter, because there aren't any antiprotons."

If there were large amounts of antimatter in our galaxy it would be very surprising, because of its readiness to react with - and destroy - normal matter. The vast majority of the universe is believed to consist of normal matter, though scientists believe there may be whole galaxies consisting of antimatter. So far, though, Nasa has not found any.