London, April 17 : Physicists have claimed to see a clear signature of dark matter - the massive, rarely interacting particles that are thought to fill the universe.
According to a report in Nature News, the discovery was made by Rita Bernabei, a physicist at the University of Rome Tor Vergata and the National Institute for Nuclear Physics.
Dark matter is believed to make up 85% of all the mass in the Universe. But unlike regular matter, such as protons and electrons, it rarely interacts with its surroundings and thus has never been spotted.
So far, physicists and astronomers have only been able to gauge its indirect effect on the motions of galaxies and the structure of the universe itself.
In 2000, Bernabei's team claimed that an earlier generation of detector had picked up a kind of dark matter known as weakly interacting massive particles (WIMPs).
The number of WIMPs striking the detector seemed to vary by season: the detector picked up more events in June than December. The team claimed the variation was due to the earth's motion through a flow of WIMPs through the Milky Way.
But other teams have failed to detect the variation.
Now, the research team at the University of Rome has confirmed a seasonal variation in dark matter detections, which, the researchers claim, is generated by Earth passing through the 'halo' of dark matter that envelops the Milky Way. The latest Italian findings back up the team's claim from 2000.
The new results arise from nearly four years of data, and they contain the same seasonal signal as in the 2000 claim.
The experiment, known as Dark Matter Large Sodium Iodide Bulk for Rare Processes (DAMA/LIBRA), is located deep underground in the Gran Sasso National Laboratory in central Italy. It consists of 25 ultrapure crystals of sodium iodide totalling around 250 kilograms in mass. he WIMPs strike the nuclei in the crystals, rattling the surrounding electrons and creating a flash of light. That flash can in turn be picked up by nearby detectors.
According to Richard Gaitskell, a physicist at Brown University in Rhode Island who studies dark matter, "It statistically looks very strong."
"If true, the results could be extremely valuable in terms of unravelling our current understanding of the universe," he added.