IceCube neutrinos give us first glimpse into the inner depths of an active galaxy

For the first time, an international team of scientists has found evidence of high-energy neutrino emission from NGC 1068, also known as Messier 77, an active galaxy in the constellation Cetus and one of the most familiar and well-studied galaxies to date. First spotted in 1780, this galaxy, located 47 million light-years away from Earth, can be observed with large binoculars. The results were published in the journal Science.

The detection was made at the U.S. National Science Foundation-supported IceCube Neutrino Observatory, a massive neutrino telescope encompassing 1 billion tons of instrumented ice at depths of 1.5 to 2.5 kilometers below Antarctica's surface near the South Pole. “Investments in Antarctic research infrastructure have advanced the field of neutrino astronomy and yielded groundbreaking insights on the nature of the universe,” says Roberta Marinelli, director of NSF’s Office of Polar Programs. 

This unique telescope, which explores the farthest reaches of our universe using neutrinos, reported the first observation of a high-energy astrophysical neutrino source in 2018. The source, TXS 0506+056, is a known blazar located off the left shoulder of the Orion constellation and 4 billion light-years away. "Answering these far-reaching questions about the universe we live in is a primary focus of the U.S. National Science Foundation," says Denise Caldwell, director of NSF's Division of Physics.

"One neutrino can single out a source," says Francis Halzen, a physicist at the University of Wisconsin–Madison and principal investigator at IceCube. "But only an observation with multiple neutrinos will reveal the obscured core of the most energetic cosmic objects. IceCube has accumulated some 80 neutrinos of teraelectronvolt energy from NGC 1068, which are not yet enough to answer all our questions, but they definitely are the next big step towards the realization of neutrino astronomy."

Unlike light, neutrinos can escape in large numbers from extremely dense environments in the universe and reach Earth largely undisturbed by matter and the electromagnetic fields that permeate extragalactic space. Although scientists envisioned neutrino astronomy more than 60 years ago, the weak interaction of neutrinos with matter and radiation makes their detection extremely difficult. Neutrinos could be key to our queries about the workings of the most extreme objects in the cosmos.