The 2026 Nobel Prize in Physics has been awarded to Francis Halzen, a Belgian-born physicist based at the University of Wisconsin–Madison, for his decisive contributions to the IceCube Neutrino Observatory and the discovery of high-energy neutrinos of astrophysical origin. The Royal Swedish Academy of Sciences announced the prize on Tuesday, saying his "vision and scientific leadership" had been fundamental to the project. Halzen, 82, was born in Tienen, a town in Belgium's Flemish Brabant province, and has worked in the United States since 1972. He told a news conference that the award was "a great surprise".
Neutrinos are subatomic particles with almost no mass and no electric charge. They pass through matter with hardly any interaction: billions cross every person on Earth each second, most of them emitted by the Sun. High-energy neutrinos from beyond our Solar System are about a billion times rarer. They come from extreme sources such as exploding stars and the regions around supermassive black holes. Ellen Moons, secretary general of the Academy, called them "ghostly messengers from space".
Catching them requires a detector on an enormous scale. In 1988, Halzen proposed using the Antarctic ice itself. IceCube, built at the geographic South Pole between 2005 and 2010, consists of 86 cables lowered as deep as 2.5 kilometres into boreholes melted with hot water. Together they carry more than 5,000 light sensors spread through a cubic kilometre of ice. On rare occasions a neutrino strikes an atomic nucleus and produces a fast charged particle, such as a muon. It emits a faint blue glow, known as Cherenkov radiation, that the sensors record. The timing and pattern of that light let scientists work out the direction the neutrino came from.
The path was not straightforward. An earlier prototype, AMANDA, was completed in 2000, and IceCube reported its first strong evidence of high-energy cosmic neutrinos in 2013. Halzen recalled that "very few thought it would work, including myself". Belgian physicist Dirk Ryckbosch compared the wait for data to sitting with a camera in a dark room, where only an occasional flash of light enters.
The result matters because neutrinos reveal what light cannot. Unlike charged cosmic rays, whose paths are bent by magnetic fields, neutrinos travel in nearly straight lines and can escape dense regions that block light. The work helped establish multi-messenger astronomy, which combines light, gravitational waves, cosmic rays and neutrinos. Louis Barson of the Institute of Physics in London said IceCube lets astronomers study phenomena that conventional telescopes cannot see. Oxford physicist Subir Sarkar said Halzen had "opened a new window on to our Universe".
The physics award is the second of this year's Nobel season, following Monday's Medicine Prize. The prize carries 12 million Swedish kronor, about $1.2 million, and will be presented on 10 December.