Antarctic IceCube observatory tracks a single neutrino to solve cosmic ray puzzle

In this artistic rendering, a blazar is accelerating protons that produce pions, which produce neutrinos and gamma rays. One neutrino’s path is represented by a blue line passing through Antarctica, while a gamma ray’s path is shown in pink. (IceCube / NASA Illustration)

An array of detectors buried under a half-mile-wide stretch of Antarctic ice has traced the path of a single neutrino back to a supermassive black hole in a faraway galaxy, shedding light on a century-old cosmic ray mystery in the process.

The discovery, revealed today in a trio of research papers published by the journal Science and The Astrophysical Journal, marks a milestone for the IceCube Neutrino Observatory at the National Science Foundation’s Amundsen-Scott South Pole Station.

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It also marks a milestone for an observational frontier known as multi-messenger astronomy, which takes advantage of multiple observatories looking at the sky in different ways. Thanks to IceCube’s alert, more than a dozen telescopes were able to triangulate on the neutrino’s source.

“No one telescope could have done this by themselves,” said IceCube lead scientist Francis Halzen, a physics professor at the University of Wisconsin at Madison.

The source of the high-energy neutrino detected last Sept. 22 appears to be a giant elliptical galaxy with a rapidly spinning black hole at its center, 3.7 billion light-years from Earth.

Such a galaxy is known as a blazar, and its signature feature is a pair of jets that spew radiation and subatomic particles along the axis of the black hole’s rotation. One of the blazar’s jets just happens to be pointed directly at Earth.

Astronomers have known about the blazar, known as TXS 0506+056, for years. But before IceCube came on the scene, they had no way of associating it or any other source with cosmic rays.