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Icy detective discovers extraterrestrial particles

The IceCube Laboratory at the Amundsen-Scott South Pole Station in Antarctica is the world's largest neutrino detector. Its computers collect raw data on neutrino activity from sensors in the ice that look for light emitted when neutrinos strike. Event filtering happens in near real-time in this lab in Antarctica. Neutrino events selected as interesting for physics studies are sent to the University of Wisconsin-Madison, where they are further studied by members of the IceCube Collaboration.
[Image courtesy of Sven Lidstrom, IceCube/NSF, March 2012]

Sensors buried below the ice may help scientists figure out where the high-energy rays that speed through space are born, a new study reports. And this is exciting as the origin of these rays, known as cosmic rays, has long been mysterious -- because cosmic rays are hard to track.

In a report published in the 22 November issue of the journal Science, a team of researchers led by the University of Adelaide's M.G. Aartsen detected particles from beyond our Solar System that can be tracked all the way to the dark corners from which they came. Those particles are called neutrinos.

Because they have no mass or charge, neutrinos don't get deflected or caught in space like cosmic rays do. But they likely have the same distant source, so studying them would be a way to understand where cosmic rays come from.

Scientists had long thought neutrinos could be helpful tools in this effort, but they've not detected any from outside our Solar System (i.e., from sources other than the Sun) since 1987.

Then, in the summer of 2012, exciting results came from the South Pole; team members analyzing data from the region's Ice Cube neutrino detector -- which had been scanning for high-energy neutrinos since 2010 -- reported two neutrinos with energies above what's expected.

The scientists started sifting through the rest of the data from Ice Cube, looking for more high-energy neutrino events. They found 26 more, including the most energetic neutrinos ever observed, and each with characteristics similar to those scientists predicted extraterrestrial neutrinos would have.

This suggests that these 28 neutrinos are from outside of the Solar System.

The scientists suspect they originated in the bright sources (like supernovae) that produce high-energy cosmic rays, which is what they will examine next. Doing so may allow them to solve the riddle of the origin of cosmic rays.