Neutrino hunters in search of the elusive, nearly massless particles believed to be created by black holes and supernovae says they've confirmed their existence using detectors buried deep beneath Antarctica.
The IceCube Neutrino Observatory, with instruments buried 8,000 feet under ice near the South Pole, has detected neutrinos streaming through the Earth from our Milky Way galaxy and, more importantly, from beyond, researchers report.
Neutrinos have little mass but so much energy they pass through most matter as if it wasn't there, but occasionally, as they pass right through the Earth, they will collide with the nucleus of an atom of matter.
The collision creates another particle, known as a muon, which gives off a special kind of light known as Cherenkov radiation.
That's what the deeply-buried detectors below Antarctica have seen; an analysis of the billions of particles passing through the detectors from 2010 and 2012 revealed exactly 21 of the high-energy muons, researchers report in the journal Physical Review Letters.
They are an unequivocal signal of high-energy cosmic neutrinos traversing space, unimpeded by planets, stars or even entire galaxies finally colliding with atoms here on Earth, they say.
"Looking for muon neutrinos reaching the detector through the Earth is the way IceCube was supposed to do neutrino astronomy and it has delivered," explains Francis Halzen of the University of Wisconsin, Madison, a physics professor and principal investigator of IceCube. "This is as close to independent confirmation as one can get with a unique instrument."
While the existence of the neutrinos has been confirmed, their actual point sources — their point of origin — remains to be identified, they researchers say.
However, because the Ice Cube detectors registered neutrinos regardless of where the rotation of the Earth had them pointed, that suggests origins beyond our own Milky Way galaxy, the researchers say.
If the neutrinos were all generated within our galaxy, the detector should find more of them when lined up with the plane of the Milky Way, they say.
"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," says study senior author Albrecht Karle, another UW-Madison physics professor and lead author of the study. "But the highest-energy neutrinos we've observed come from random directions."
"It is sound confirmation that the discovery of cosmic neutrinos from beyond our galaxy is real," he concludes.
The neutrinos may yield clues to the origins of the Universe's most energetic processes and reveal secrets of fundamental particle physics and even the origins of dark matter, he suggests.