Francis Halzen Wins the Physics Nobel for an Antarctic Ice Observatory That Caught Cosmic High-Energy Neutrino

STOCKHOLM — Francis Halzen won the 2026 Nobel Prize in Physics on Tuesday for the IceCube Neutrino Observatory, a cubic kilometer of instrumented ice at the South Pole that detected high-energy neutrinos from outside the solar system.

The Royal Swedish Academy of Sciences cited the University of Wisconsin–Madison professor "for decisive contributions to the IceCube Neutrino Observatory and the discovery of high-energy neutrinos of astrophysical origin." The prize is 12 million Swedish kronor. He is the sole laureate. He is Belgian-born and a U.S. citizen.

Halzen first set out the idea in 1988: a neutrino that hits a nucleus in clear glacial ice produces a flash of light, and sensors frozen into that ice can track it. IceCube, backed by the National Science Foundation, buried those sensors in a cubic kilometer of Antarctic ice and found a flux of high-energy neutrinos from cosmic accelerators. Neutrinos barely interact with matter. They cross the universe without the scattering that bends light and charges, which is why they can carry information from regions ordinary telescopes cannot see.

"Francis Halzen has led an international team of researchers and engineers who have provided us with a fantastic instrument. His tenacity and scientific vision has paved the way for a new kind of astronomy," said Mark Pearce, chair of the Nobel Committee for Physics. Eva Olsson of the academy said the particles "open the door to distant galaxies and tell us about the processes of exploding stars."

Halzen said the call was a relief more than a shock. "It's a great relief for me because this was not totally unexpected, and around this time of the year I always felt miserable because I didn't win the prize and thought it was terrible for my collaborators who deserved it so much," he said. "It's a great relief for me to finally deliver the recognition that this great collaboration deserves. This was a great surprise and is a celebration of a very unusual project." He credited "the diligence and hard work of the many wonderful collaborators I've had the pleasure to work with."

He also said he had not been sure it would work. "I have to emphasise how lucky I was. Because when we started this project, everybody realised this was maybe a good idea, but very few thought it would work, including myself." The goal, he said, was simple: "We could catch them in ice." He called the observatory a window on the universe, and said the field is not finished. "This is a new way of looking at the universe, and it will take bigger telescopes, many more telescopes, to become real astronomy. And what this will bring is impossible to predict."

Erin O'Sullivan, spokesperson for the IceCube collaboration, said the group was proud of the research and of a prize that was well deserved. "Francis continues to inspire us with the potential of the future of the field, where we can move from the first discoveries to robust detections," she said. The collaboration expects first science data from an IceCube upgrade later this year.

Belgian Prime Minister Bart De Wever congratulated Halzen on "a life dedicated to unraveling the greatest secrets of the cosmos through its most minuscule manifestations."

The medicine prize, announced Monday, went to Karl Deisseroth, Peter Hegemann and Georg Nagel for optogenetics. Physics this year is a single name on a detector that took decades to freeze into the ice. Halzen's own account is that the collaborators earned it and that he was not certain the ice would work. The academy's account is that the ice did, and that the flashes in it opened a kind of astronomy that did not exist when he proposed it in 1988.