Francis Halzen received the Nobel Prize in Physics on 6 October for his contributions to neutrino physics.Credit: Althea Dotzour/University of Wisconsin–MadisonBelgian-born physicist Francis Halzen has won the 2026 Nobel Prize in Physics for his work on detecting high-energy elusive particles called neutrinos that come from deep space.
It is the first time since 1992 that the physics prize has been awarded to only one winner.
“It was a great surprise and I obviously didn’t expect it,” said Halzen, speaking to the Nobel press conference after the prize was announced.
The IceCube Neutrino Observatory — an array of 5,160 sensors — was completed in 2010 at a cost of US$271 million, mainly funded by the US National Science Foundation.
Francis Halzen, a pioneer in neutrino physics, is announced as the winner of the 2026 Nobel Prize in Physics.
Francis Halzen received the Nobel Prize in Physics on 6 October for his contributions to neutrino physics.Credit: Althea Dotzour/University of Wisconsin–Madison
Belgian-born physicist Francis Halzen has won the 2026 Nobel Prize in Physics for his work on detecting high-energy elusive particles called neutrinos that come from deep space.
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His pioneering contribution is the founding of a giant detector, the IceCube Neutrino Observatory at the South Pole. Its results have helped to found the fields of neutrino and multi-messenger astronomy, which enable physicists to unlock the mysteries of the Universe through observing highly energetic events from deep in the cosmos.
Halzen, who is based at the University of Wisconsin–Madison, takes home the prize of 12 million Swedish kronor (US$1.2 million), announced by the Royal Swedish Academy of Sciences in Stockholm on 6 October. It is the first time since 1992 that the physics prize has been awarded to only one winner.
“It was a great surprise and I obviously didn’t expect it,” said Halzen, speaking to the Nobel press conference after the prize was announced. “This reflects on the really courageous people who joined me in this project when really no respectable conservative physicist would have joined me, but many talented people did and that’s why I’m here.”
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Neutrinos are the second most common particle in the Universe, after photons. More than one billion neutrinos pass through a human hand every second, but high-energy neutrinos are extremely rare and hard to detect. IceCube was designed to study the particles after they fly out of some of the most energetic environments in the Universe, such as supernovae and powerful explosions called γ-ray bursts. Because neutrinos pass straight through matter, they allow researchers to draw a straight line back to these events, providing them with a unique way of probing astrophysical phenomena.
Halzen is “a father figure for neutrino astronomy”, says Paschal Coyle, a neutrino physicist at Aix-Marseille University in France and the former spokesperson of KM3NeT, a similarly large observatory being built in the Mediterranean Sea.
The IceCube Neutrino Observatory at the South Pole was Nobel prizewinner’s Francis Halzen’s brainchildCredit: Ilya Bodo, IceCube/NSF
Looking into the cosmos
Despite being all around us, neutrinos are fiendishly difficult to detect because they are unaffected by magnetic fields and rarely ever interact with matter. In the 1980s, Halzen had the idea to use detectors attached to strings, lowered more than 1.5 kilometres into holes drilled into the clear ice of the Antarctic, which is free from many types of interference. There he hoped they would detect the rare and faint flashes of light that occur when a fast-moving neutrino hits an atom.
As long as the volume of the set-up was big enough, Halzen theorized that it could catch neutrinos and their direction of travel would allow researchers to trace their origins in the cosmos (see ‘Neutrino observatory’).
The IceCube Neutrino Observatory — an array of 5,160 sensors — was completed in 2010 at a cost of US$271 million, mainly funded by the US National Science Foundation. It now involves a collaboration of about 450 researchers. “After one and a half decades of development, and another decade of construction, there was no guarantee we would ever see anything,” Halzen, principal investigator of IceCube, told APS News last year. “Many people thought we wouldn’t, but we did.”
Within two years, the detector had observed energetic neutrinos from beyond the Milky Way. In 2013, the IceCube collaboration reported1 finding a population of neutrinos with energies so high that they could not have been produced anywhere in the Solar System. The discovery helped to establish the field of neutrino astronomy2.
“The biggest risk we took is that nobody knew if the kilometre cube detector was actually large enough to detect neutrinos beyond our atmosphere from the Universe,” Halzen told the Nobel press conference. “But it only took two years to detect that.”
“We found evidence for neutrinos coming from supermassive black holes in other galaxies, and they shine so strongly that when you look at a neutrino sky you don’t see the Milky Way.”
In 2013 and 2014, IceCube discovered three neutrinos with energies that blew all others out of the water. Nicknamed Bert, Ernie and Big Bird, they had energy levels measured in petaelectronvolts (a quadrillion electronvolts) — thousands of times more energetic than those produced in Earth’s most advanced particle colliders. And three years later, the collaboration made a long-awaited discovery of a high-energy neutrino that they could, for the first time, trace back to a specific source — a distant galaxy called TXS 0506+056, often referred to as ‘the Texas event’.
IceCube detectors are sunk deep into Antarctica’s ice — which is free from many types of interference — to catch neutrinos at high energies. Credit: Yuya Makino, IceCube/NSF
The source was a blazar, a type of violent galaxy that produces bright flares of light and harbours a supermassive black hole at its core. In 2018, seven papers described the galaxy using observations from a suite of telescopes and a variety of methodologies.
‘Undisputed force’
Halzen was born in Tienen, Belgium, in 1944 and studied at the nation’s University of Louvain in Louvain-la-Neuve. He trained as a particle physicist, working at CERN, Europe’s particle-physics laboratory near Geneva, Switzerland, before moving to Wisconsin in 1971.
As the principal investigator for IceCube from its original proposal in 1999, Halzen was the project’s “undisputed” driving force, says IceCube senior member Elisa Resconi, an astroparticle physicist at the Technical University of Munich in Germany. She says that Halzen deserves credit for having pushed for an experimental concept that many researchers initially saw as “the weirdest in the world”. The logistical challenges of building a large-scale facility not just in Antarctica, but at the South Pole, were enormous.
Francis Halzen, a pioneer in neutrino physics, is announced as the winner of the 2026 Nobel Prize in Physics. Credit: Christine OLSSON/TT NEWS AGENCY/AFP via Getty
“He has such a charisma that when he enters a room, everyone turns around,” Resconi says. He also takes special effort to cultivate talent — and can usually remember the names and academic histories of each member of the IceCube collaboration.
