Ghostly Particles from Outer Space Detected in Antarctica

The IceCube Lab at the South Pole, lit up by star trails in this photo taken in July 2015.

(Image credit: IceCube Collaboration)

Buried deep in the Antarctic ice, an observatory has spotted ghostly, nearly massless particles coming from inside our galaxy and points beyond the Milky Way.

Finding these cosmic neutrinos not only confirms their existence but also sheds light on the origins of cosmic rays, the researchers said.

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Though they don't interact much with matter, occasionally one will hit an atomic nucleus on Earth. When that happens the neutrino generates a particle called a muon. That's what scientists look for when seeking neutrinos — the muons move faster than the speed of light in a solid (ice in this case) and generate light waves, like the wake of a boat in water, called Cherenkov radiation. They also show the paths of the neutrinos. (The speed of light is constant in a vacuum, but it is slower in a medium like ice or glass — this is what causes refraction. So the muons aren't actually breaking the speed of light limit).

The IceCube project found neutrinos from outside our galaxy in 2013, but to confirm that detection the researchers, led by a team at the University of Wisconsin-Madison, had to make sure these neutrinos weren't coming from sources within our own galaxy (such as from the sun). To do so, they looked for neutrinos with similar energies that were coming from all directions at the same rate, meaning they are independent of the Earth's rotation and orbit around the sun — the only way that can happen is if the source is outside the galaxy.

Those 20 neutrinos, called muon neutrinos, came from the opposite direction, but at approximately the same rate, as similar neutrinos observed in earlier runs. Since the rate at which they showed up was about the same throughout the observation, it means it didn't matter where the observatory was pointed as a result of the daily rotation and yearly orbit of the Earth — the result predicted for extragalactic neutrinos. [Wacky Physics: The Coolest Little Particles in Nature]

Those observations also told them something else: The energies of the muon neutrinos, and their numbers, didn't fit well with several models of their origins. The scientists don't address it deeply in their study ("We leave that to theorists," Karle said), but the data appear to show these muon neutrinos are probably not coming from gamma-ray bursts (GRBs), which are highly energetic events in space.

Other possibilities are galaxies going through bouts of rapid star formation, or masses of gas and dust that surround black holes at the galactic centers. As atoms get pulled into the maw of a black hole, they slam into each other more often at higher energies. Eventually some produce pions, neutrinos and photons. If that were the case, Karle said, then one would expect a nearly one-to-one ratio of high-energy neutrinos to accompanying photons. But that hasn't been confirmed or refuted yet.

Jesse Emspak is a contributing writer for Live Science, Space.com and Toms Guide. He focuses on physics, human health and general science. Jesse has a Master of Arts from the University of California, Berkeley School of Journalism, and a Bachelor of Arts from the University of Rochester. Jesse spent years covering finance and cut his teeth at local newspapers, working local politics and police beats. Jesse likes to stay active and holds a third degree black belt in Karate, which just means he now knows how much he has to learn.