Scientists have uncovered more evidence to support the existence of nearly massless high-energy particles called cosmic neutrinos.
A team of researchers in Antarctica used the IceCube Neutrino Observatory to detect 21 ultra high-energy muons, which are rare secondary particles that are formed when neutrinos interact with other particles, the University of Wisconsin-Madison reported. These findings provide independent confirmation from 2013 observations that neutrinos exist in our galaxy and beyond.
Neutrinos are born from some of the universe's most violent events, and are accelerated to energy levels that exceed the capabilities of the Large Hadron Collider (LHC) by a factor of more than a million. To make these recent findings, scientists pointed the Ice Cube Observatory through the Earth to the Northern Hemisphere sky. This technique allows the Earth to filter out confusing background muons that occur when cosmic rays crash into Earth.
"Looking for muon neutrinos reaching the detector through the Earth is the way IceCube was supposed to do neutrino astronomy and it has delivered," said Francis Halzen, a UW-Madison professor of physics and the principal investigator of IceCube. "This is as close to independent confirmation as one can get with a unique instrument."
Between May 2010 and May 2012, IceCube recorded more than 35,000 neutrinos but only about 20 had energy levels indicating astrophysical or cosmic sources. Using a large area of Antarctic ice to create a detector gave the researchers the ability to capture the signature of the rare neutrino collision. These types of events create muons that bring with them a trail of Cherenkov light believed to mirror the trail of their parent nuetrinos. The "optical sonic booms" created when neutrinos smash into other particles can be picked up by the powerful optical sensors in the IceCube detector array, potentially pointing back to a specific source. While these new findings confirm the existence of astrophysical neutrinos, an exact source of these high-energy particles is yet to be identified.
The neutrinos looked at in this latest research have energy levels identical to those observed in the Southern Hemisphere. This suggests neutrinos are created outside of the Milky Way, because if they were created within the realms of our galaxy the IceCube detector would light up when observing the galactic plane.
"The plane of the galaxy is where the stars are. It is where cosmic rays are accelerated, so you would expect to see more sources there. But the highest-energy neutrinos we've observed come from random directions," said Albrecht Karle, a UW-Madison professor of physics. "It is sound confirmation that the discovery of cosmic neutrinos from beyond our galaxy is real."
The findings were published in a recent edition of the journal Physical Review Letters.
