News in Science

IceCube detects neutrinos from outer space

Bright sparks Mysterious high energy particles, possibly the result of the most violent collisions in our universe, have been detected for the first time.

"It's opened a new window on the Universe," says Dr Gary Hill of the University of Adelaide. "This discovery makes way for a new type of astronomy that we can use to probe the far reaches of the galaxy and beyond."

The discovery was made using the world's largest particle detector, the Antarctica IceCube experiment located at the South Pole.

"This is the first solid evidence for high-energy neutrinos coming from cosmic accelerators beyond our own solar system," says Hill who is one of the study's authors, which appears today in the journal Science.

Neutrinos are subatomic particles, which interact very weakly with all other matter.

They are produced through cosmic ray particle collisions; in the atmosphere, centre of stars, nuclear reactions, and supernovae explosions. But astronomers suspect other so far unknown cosmic accelerators are also generating them.

However, because neutrinos interact so weakly with matter, they are extremely difficult to detect.

To detect neutrinos, the IceCube detector uses 5160 sensors placed in a grid pattern buried in Antarctic ice sheet, one and a half kilometres below the surface.

Trillions of neutrinos pass through the cubic kilometre of ice that IceCube is monitoring. When one of these particles collides with an oxygen atom in the ice it produces a faint blue spark. The flash of light tells scientists the direction and energy that a neutrino had when it flew into the detector.

The first hints of extraterrestrial high-energy neutrinos came in April 2012 with the detection of two 'collision events' of more than 1000 TeV, later named Bert and Ernie and reported in the journal Physical Review Letters.

This latest reported confirms an additional 26 'weaker' collision events of about 30 TeV.

Cosmic origins

Neutrinos are unaffected by magnetic fields, so it should be possible to trace them back to their source.

"At least half of these have properties and energies inconsistent with being produced in Earth's atmosphere," says Hill.

"They were probably made in the centre of active galaxies, possibly quasars. The question is whether they're made in our own galaxy or are extragalactic."

According to Hill the neutrinos detected so far were spread across the sky and occurred at different times, indicating they weren't caused by a single event or from a single source.

"The thing to do now is to take more data and run the detectors for a longer time, and if there is a preferred direction in the sky, then that will start to show up."