Halzen wins the physics Nobel for IceCube's South Pole neutrinos

Francis Halzen won the 2026 Nobel Prize in Physics on Tuesday for building a telescope out of Antarctic ice. The Royal Swedish Academy of Sciences gave the award to the University of Wisconsin-Madison physicist 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, about 1.2 million dollars at the rate Reuters used.

Halzen is 82, Belgian-born, and a US citizen. He first set out the South Pole idea in 1988. The Academy said his vision and scientific leadership were fundamental to IceCube, a cubic kilometre of ice fitted with light sensors. Construction finished in 2011. More than 5,000 optical modules sit in the ice and wait for a rare collision. When a neutrino hits a nucleus, it can produce a flash of blue Cherenkov light. The modules time that flash and reconstruct a track.

Neutrinos barely interact with matter. They cross the Earth without bending or losing energy in the way charged particles do. That is why they can point back to the violent place that made them: a supernova, a gamma-ray burst, or the region around a black hole or a neutron star. Ordinary light from those places can be blocked by dust and gas. The neutrino is not. Halzen told the Academy's news conference that the goal had been simple: catch them in ice, and open a window on the universe.

He also said he had been lucky. When the project started, he told reporters, very few people thought it would work, including him. On the IceCube site he called the prize a relief, because it recognised a collaboration rather than a single instrument. Erin O'Sullivan, spokesperson of the collaboration, said the group was proud of the research and that Halzen was still pushing the field from first detections toward firmer ones. Mark Pearce, chair of the Nobel Committee for Physics, said Halzen had led an international team of researchers and engineers who had provided a remarkable instrument.

The first high-energy neutrinos showed up soon after the array was complete. A few years later the collaboration published evidence that some of them had to come from far outside the solar system. That is the result the citation names. Smithsonian magazine called him Neutrino Man in 2014, when it gave him an Ingenuity Award and described the experiment as the start of a new kind of astronomy. The 2015 physics prize had already gone to Takaaki Kajita and Arthur McDonald for showing that neutrinos have mass. Halzen's prize is for a different job: using the particle as a messenger from distant accelerators.

The array is not finished as a programme. IceCube expects the first science data from its Upgrade later this year. A larger plan, IceCube-Gen2, would cover 8 cubic kilometres and is scheduled to operate in 2033. The collaboration says that array should record about ten times as many neutrinos, including weaker ones. Halzen told Reuters the main results of the work were still ahead, and that it was too early to say exactly what the detector would reveal.

The practical constraint is volume. Cosmic neutrinos at these energies are rare, so the target has to be enormous and clear. South Pole ice is both. The laboratory building sits on the surface at Amundsen-Scott Station. The sensors are below it, frozen in place, cabled back to the surface. Data go to the collaboration, which the project has described as hundreds of scientists across many countries. The Academy's press contact for the announcement was Eva Nevelius. Committee members Ulf Danielsson and Mark Pearce were listed as the experts for questions.

One person took the medal. The citation still describes a machine that only a collaboration could run: a cubic kilometre, more than 5,000 sensors, a 2011 completion, a published flux from outside the solar system, an upgrade due this year, and a 2033 plan for 8 cubic kilometres. The 12 million kronor goes to Halzen. The next numbers the field will watch are the Upgrade's first science data and whether Gen2 stays on the 2033 date.