By Doreen Walton

Science reporter, BBC News

Some scientists believe dark matter (in pink) is everywhere in the universe Researchers in the US say they have detected two signals which could possibly indicate the presence of particles of dark matter. But the study in Science journal reports the statistical likelihood of a detection of dark matter as 23%. Deep underground in a lab in Minnesota experiments to detect WIMPS, or Weakly Interacting Massive Particles have been going on since 2003. Scientists are currently developing an even more sensitive experiment. "It's a very difficult situation," said Professor Jodi Cooley from Southern Methodist University, Dallas in the US, who led the research. "In some ways I feel we've been very unlucky. It's a very exciting time in the field

Professor Jodi Cooley,

Southern Methodist University "Either we had a statistical fluctuation in our background or it could be that these two events are evidence of dark matter but there weren't enough of them to be sure. "We can't rule them out as being a signal but we can't conclude that they are a signal." The Cryogenic Dark Matter Search (CDMS), an experiment designed to detect the dark matter particles, is a joint effort by several US universities and institutes. The scientists describe dark matter as being "the gravitational scaffolding that caused normal matter to coalesce into the galaxies we see today". Ordinary matter - gas, stars, planets and galaxies - is thought to make up less than 5% of the Universe. The rest of the cosmos is unseen, 70% is thought to be "dark energy" and 25% is believed to be dark matter. Different theories Some scientists believe dark matter is made up of WIMP subatomic particles. These are thought to have a similar mass to the nuclei that give each atom the majority of its mass, but are predicted to "bounce off" rather than interact with any other matter. This would make the particles themselves impossible to find. So the detectors in the CDMS experiment are designed to pick up the tiny amount of energy that Wimps leave behind as they scatter - the only clue that might remain. Other scientists argue that that the dark substance consists of everyday matter, but that this ordinary matter, referred to as Massive Astrophysical Compact Halo Objects (Machos), happens to radiate little or no light. Professor Cooley hopes that the new experiment that's being developed will speed up the process of looking for evidence of dark matter. "It's a very exciting time in the field," she added.



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