Australian scientists begin to shine light into invisible dark matter

Australian scientists believe they are well on the way toward solving one of the universe’s greatest mysteries, the nature of invisible dark matter.

The Oscillating Resonant Group AxioN ( ORGAN) experiment, Australia’s first major dark matter detector, has just completed a search for a particle called an axion – believed by many cosmologists and physicists to be a likely component of dark matter.

Dark matter, which is believed to form a large proportion of the galaxy, does not absorb, reflect, or emit electromagnetic radiation, making it exceptionally difficult to detect.

Explaining the project in an article published in the Conversation on Tuesday, physicist Dr Ben McAllister from the University of Western Australia, said ORGAN had placed new limits on the possible characteristics of axions and had, therefore, helped to narrow down the elusive search for them.

McAllister said scientists believed that axions can be converted into particles of light, known as photons, if they are subjected to a strong magnetic field.

“This is good news, because this is exactly what ORGAN does,” he said.

“It engineers the correct conditions for axion- photon conversion and looks for weak photon signals, which are little flashes of light generated by dark matter passing through the detector.”

Prior to the creation of ORGAN, scientists were hampered by temperatures generated by the magnetic fields triggering random flashes of light, or noise as they call it, which has made it hard to detect the faint dark matter signals.

“To work around this, we’ve placed our resonator in a ‘ dilution refrigerator,’” he said. “This fancy fridge cools the experiment to cryogenic temperatures, about - 273 C, which greatly reduces the noise.”

In a separate article published in SciTechDaily on Monday, McAllister expounded on their progress.

“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,” he said.

“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.”

McAllister said the project was just the first phase of a multi- year search for axions with the future work to be even more exhaustive.

“We’re currently preparing the next experiment, which will be more sensitive and target a new, as- yet- unexplored mass range,” he said.

Explaining the significance of their quest, McAllister said, “We never would have discovered electricity, or radio waves, if we didn’t pursue things that, at the time, appeared to be strange physical phenomena beyond our understanding.”

“Dark matter is the same.”