Francis Halzen wins 2026 Nobel Prize in Physics for IceCube neutrino observatory

The 2026 Nobel Prize in Physics goes to Francis Halzen of the University of Wisconsin-Madison, Ars Technica and Nature report. According to Ars Technica, the prize recognizes his “decisive contributions to the IceCube Neutrino Observatory” and the discovery of high-energy neutrinos produced by astrophysical sources. Halzen drove the design and construction of IceCube, a detector at the South Pole that uses a cubic kilometer of Antarctic ice to record neutrinos from deep space.

Speaking by phone from Italy to the news conference in Stockholm, Halzen said “It was a great surprise, and I obviously didn’t expect it,” and stressed that the work came from a “large collaboration”. Particle physicist Danielle Norcini of Johns Hopkins University called him the scientific visionary behind the project, and American Institute of Physics CEO Michael Moloney said Halzen had led a decades-long effort to make Antarctic ice work as a neutrino telescope.

The Belgian-born Halzen proposed a neutrino observatory at the South Pole in 1988. Ars Technica reports that he merged two earlier proposals, one using water as a detection medium and one listening for neutrino signals in Antarctica with radio receivers, and concluded that ice would work even better. His team melted holes roughly a kilometer deep with hot water and lowered cables carrying light sensors into them. A first detector, AMANDA, was hampered by bubbles in the upper ice that scattered light; the ice proved very pure below 1400 meters, but AMANDA was too small, and IceCube took its place.

IceCube began operating in 2011. Its 5,160 light sensors hang on 86 cables in the ice and pick up the blue and ultraviolet light given off when a passing neutrino strikes an atomic nucleus. Halzen said it took only two years to show that the detector could see neutrinos from beyond the atmosphere. In 2014 it recorded three neutrinos of record energy, nicknamed Bert, Ernie and Big Bird. In 2017 a high-energy neutrino was traced for the first time to a specific source, the blazar TXS 0506+056; Nature describes this as IceCube's first multi-messenger discovery. In 2022, after analyzing ten years of data, the team reported an excess of 79 neutrinos that made the active galaxy Messier 77 a strong candidate for a neutrino source.

The observatory is still growing. Ars Technica reports that an upgrade finished in February added five strings of sensors near the bottom center of the array, along with 600 new light sensors and calibration instruments, and that the National Science Foundation committed $53 million last month to keep it running for the next five years. Halzen said the results so far still fit Standard Model neutrino physics, which he would like to see broken, and joked that he hopes the prize will help a proposal he is working on get approved.