Dark matter 'seen for first time'
Dark matter 'seen for first time'
Scientists may have caught their first glimpse of dark matter, the mysterious hidden substance believed to give structure to the universe.
By Richard Alleyne, Science Correspondent
Published: 7:00PM GMT 11 Feb 2010
After nine years of searching, detectors buried 2,000ft underground in an old US iron mine registered two "hits" by what could turn out to be dark matter particles.
Both bear the hallmarks of "weakly interacting massive particles" or "Wimps", one of the most likely dark matter candidates.
But frustratingly, two detections are not quite enough to clinch the discovery.
There is still a one in four chance that the results, published by the journal Science, are due to accidental background "noise".
The scientists say five detections would be sufficient to confirm the presence of Wimps.
Physicists came up with the theory of dark matter to explain strange anomalies in the rotational speed and clustering of galaxies.
The total mass of all the stars, dust and gas in the galaxy clusters was five times too little to account for the gravitational effects observed.
Scientists were forced to conclude that some other missing material was present, described as "dark" because it was invisible and neither reflected nor absorbed light.
Dark matter is now estimated to make up as much as 23 per cent of the cosmos.
It is believed to play a central role in the evolution of galaxies and large scale structure of the universe.
Without dark matter, galaxies would not group together to form clusters and superclusters. Our galaxy, the Milky Way, belongs to a cluster known as the "Local Group".
No-one knows what dark matter is, but particle physics points to the likelihood of them being Wimps.
Wimp particles are dubbed "weakly interacting" because despite having mass they have little or no effect on ordinary matter.
This makes them extremely difficult to detect. But scientists believe it should be possible to "catch" Wimps by looking for small amounts of energy released when they randomly bounce off ordinary atoms.
The Cryogenic Dark Matter Search II (CDMS II) observatory, located nearly half a mile underground in the disused Soudan iron mine in Minnesota, is designed to do just that.
At its heart are 30 germanium and silicon detectors frozen to minus 273.1C - less than a degree above "absolute zero", theoretically the coldest temperature in the universe.
Unlike other particles, weakly interacting Wimps would be able to pass straight through the thick layers of earth and rock to reach the detectors.
Dr Tarek Saab, from the University of Florida at Gainesville, US, one of dozens of physicists working on CDMS II, said: "Many people believe we are extremely close - not just us, but other experiments.
It is expected or certainly hoped that in the next five years or so, someone will see a clear signal."
But he acknowledged the current evidence was not quite strong enough.
"With one or two events, it's tough," he said. "The numbers are too small."
Dark matter 'seen for first time' - Telegraph
Close, but no cigar ............... yet. Interesting stuff though.
