Sheffield team casts light on 'dark' matter

Wednesday, September 15, 1999

By Sheila Jones

Scientists in Sheffield believe they are close to resolving the biggest mystery of astronomy.

For years, the scientific world has struggled to identify the 90 per cent of the universe that cannot be seen with conventional telescopes and observatories.

Researchers say that this "dark matter" is probably made from exotic particles called "wimps", or weakly interactive massive particles. These sub-atomic particles created in the Big Bang fly across the universe at 1m kilometres an hour, passing through matter including the sun, the earth and its inhabitants.

"Wimps are very difficult to see because they travel through the entire mass of the earth without anyone having felt or known about it," Susan Cartwright, senior lecturer in physics and astronomy at the University of Sheffield, told the British Association. "The problem is how to find something that can pass through material as if it was not there."

Wimps have no atomic charge and their flight path is unaffected by galactic gravity. They usually leave no trace, but sometimes collide with atoms, giving off light. Head-on collisions between atoms and galactic wimps are giving researchers their first indications of their existence.

To measure the effects of these collisions and accumulations, the researchers went underground and under the sea to cut out interference from other light sources and from radioactivity. Experiments are being carried out at asite one mile below ground in Boulby salt mine in Yorkshire.

"We had to go deep underground to get away from cosmic rays," said Neil Spooner, reader in the department of physics and astronomy at the University of Sheffield, which is leading the research. "The site also benefits from the fact that salt has very low natural radioactivity."

The team believes measurements taken over the past year indicate the existence of wimps. "We have found evidence of . . .unexpected and exciting events," said Mr Spooner.

This was not definitive evidence that wimps existed, but it was an important step towards "pinning down this elusive stuff". The precise nature of dark matter was likely to be revealed within the next few years.

Copyright The Financial Times Limited