Aussie scientists join dark matter quest

While science may still be in the dark about what dark matter is, it now has a better idea of what it isn't thanks to the University of Western Australia's ORGAN Experiment.

After four years of preparation, the country's first major foray into so-called antimatter or dark energy detection has completed a substantive search for hypothetical elementary particles known as axions.

The result, according to PhD student Aaron Quiskamp, means science's leading minds can rule out a popular theory about the nature of dark matter, narrowing the possibilities for what it could be.

And why is that important?

Dark matter is believed to account for about 85 per cent of all matter in the universe and has a significant influence on its structure and evolution.

Unfortunately, though, it doesn't absorb, reflect or emit light and is therefore hard to locate.

Ms Quiskamp says he and his colleagues have performed the most sensitive search so far for axion dark matter in a particular mass range.

"Although we didn't find any, it's very exciting because it's Australia's first large-scale, long-term direct dark matter detection experiment," he said.

"It's also given us useful information about what axion dark matter isn't, which tells future axion searches across the globe where not to look."

Dr Ben McAllister, a physicist with the Australian Research Council, says numerous experiments around the globe are testing hypotheses about what dark matter is.

"We're trying to rule out all the possible candidates and by the process of elimination figure out which one is correct," he said.

"Because we don't know how heavy the axion is, if it even exists, we need multiple experiments searching the different mass ranges predicted by the theory."

The ORGAN Experiment is the first to use axion haloscope detector.

"The idea ... is to try and detect the dark matter by converting it into well-known particles called photons, which are like tiny flashes of light," Dr McAllister said.

"When we don't see any little flashes, as was the case this time, we instead place exclusion limits, where we rule out axions that our experiment would have been sensitive to.

"Then, we tell the rest of the dark matter community 'no dark matter here' and move on to search for axions of a different mass."

Mr Quiskamp says the team should begin its next search later this year, with improvements being made to achieve greater sensitivity and wider-ranging coverage.

Australian Associated Press