Francis Halzen, a physicist at the University of Wisconsin–Madison, has been awarded the 2026 Nobel Prize in Physics for his decisive contributions to the IceCube Neutrino Observatory and the discovery of high-energy neutrinos of astrophysical origin. The announcement was made by the Nobel Committee for Physics, recognising work that has opened a new window on the universe.
Neutrinos are subatomic particles that are electrically neutral and rarely interact with matter, allowing them to travel vast cosmic distances unimpeded. More than a billion neutrinos from the sun pass through a human hand every second, but Halzen's work focuses on the far rarer, high-energy neutrinos that originate in the most violent events in the cosmos. Because these particles barely interact, they can carry information about distant cosmic sources that cannot be obtained through other means.
Mark Pearce, chair of the Nobel Committee for Physics, described neutrinos as «ghost-like messengers from the cosmos». He said their detection offers «a way of bringing us information about distant cosmic sources which we're unable to acquire in other ways».
Halzen first proposed in 1988 that the Antarctic ice could serve as a neutrino detector. Over the following decades, he spearheaded an international collaboration of more than 450 people from 58 institutions in 14 countries to build the IceCube Neutrino Observatory. The detector consists of thousands of light sensors buried two kilometres beneath the surface of the ice, in deep holes drilled using hot water. When neutrinos shoot through the Earth, they occasionally interact with the ice, creating Cherenkov radiation — a faint blue light. The network of sensors allows scientists to trace the particles' trajectory back to their origin, revealing vital information about their formation.
Halzen calculated that a neutrino collector one cubic kilometre in size would detect about one neutrino per day. The experiment was completed in 2011, and the first neutrinos were detected just two years later. Speaking by phone at the press conference, Halzen said: «When I reflect on this moment 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. So this was kind of an adventure where success was not guaranteed and we were lucky to overcome the various challenges. It was a long journey but finally it worked.»
He added that he hopes the prize will reflect on the collaborators who worked on the project in its early days. «I hope it reflects on the courageous people who joined me on this project. Many talented people joined me on this journey,» he said. He also expressed gratitude to his university, noting: «I was lucky to be in the right place when this idea came up.»
The IceCube detector has since made numerous further discoveries. In 2017, it helped identify the first definitive source for a single high-energy cosmic neutrino: a blazar called TXS 0506+056, which was blasting a huge jet of energy towards Earth. In 2023, it identified neutrinos from within our own galaxy, the Milky Way, which are typically overwhelmed by stronger signals from the rest of the universe.
Halzen said he was surprised by the award. «It was a great surprise and I didn't expect it. It's a great pleasure,» he said. When asked what he would do for the rest of the day, he replied that he was working on a proposal and hoped the prize would help get it approved.
The prize will be awarded in Stockholm on 10 December and is worth SEK 12 million, about $1.2 million. The recognition underscores the growing importance of neutrino astronomy in understanding the universe's most energetic phenomena.