Nobel Prize in Physics awarded for the detection of cosmic neutrinos

Belgian-born physicist Francis Halzen has won the 2026 Nobel Prize in Physics for his work detecting elusive high-energy particles called neutrinos from the depths of space.

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His pioneering contribution was the creation of a giant detector, the IceCube Neutrino Observatory, at the South Pole. His results helped found the fields of neutrino and multimessenger astronomy, which help physicists unlock the mysteries of the Universe by observing highly energetic events from deep in the cosmos.

Halzen, who is based at the University of Wisconsin-Madison, wins the entire 12 million Swedish crown ($1.2 million) prize, announced by the Royal Swedish Academy of Sciences in Stockholm on October 6. This is the first time since 1992 that the physics prize has been awarded to a single winner.

“It was a big surprise and I obviously didn’t expect it,” Halzen said, speaking at the Nobel press conference after the award was announced. “It reflects the really courageous people who joined me in this project when 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 a billion neutrinos pass through a hand every second, but high-energy neutrinos are extremely rare and difficult to detect. IceCube was designed to study particles as they exit some of the most energetic environments in the Universe, such as supernovae and y-bursts of rays. Because neutrinos pass directly through matter, they provide a direct link to these events, giving researchers a unique way to study astrophysical phenomena.

Halzen is “a father figure for neutrino astronomy,” says Paschal Coyle, a neutrino physicist at Aix-Marseille University in France and a spokesperson for KM3NeT, a similarly sized observatory being built in the Mediterranean Sea.

Looking into the cosmos

Although they are all around us, neutrinos are extremely difficult to detect because they are unaffected by magnetic fields and rarely interact. In the 1980s, Halzen came up with the idea of ​​using detector wires, lowered more than 1.5 kilometers into holes drilled into Antarctica’s transparent ice – free of many types of interference – to detect the rare, faint flashes of light when a fast-moving neutrino hits an atom.

As long as the volume was large enough, Halzen hypothesized that the facility could capture neutrinos and their trajectory would reveal the direction they came from, allowing researchers to trace their origins in the cosmos (see “Neutrino Observatory”).

The IceCube Neutrino Observatory – an array of 5,160 sensors – was completed in 2011 at a cost of $271 million, funded by the US National Science Foundation. It now involves a collaboration of more than 450 researchers. “After a decade and a half of development and another decade of construction, there was no guarantee that we would ever see anything,” Halzen, IceCube’s principal investigator, told APS News in 2025. “A lot of people thought we wouldn’t, but we did.”

In two years, the detector had observed neutrinos coming from beyond the galaxy and exhibiting extreme energies. In 2013, IceCube published a result¹ showing that there was a population of neutrinos at energies so high that they could not have been produced anywhere in the solar system, and establishing the new field of neutrino astronomy.

“The biggest risk we took was that no one knew if the kilometer detector was actually big enough to detect neutrinos from the Universe beyond our atmosphere and that was our biggest risk. But it only took two years to detect it,” Halzen said at the Nobel press conference.

“We’ve found evidence of neutrinos coming from supermassive black holes in other galaxies, and they shine so brightly that when you look at a neutrino sky, you don’t see the Milky Way.”

In 2014, IceCube discovered three neutrinos with energies that blew all the others out of the water. Nicknamed Bert, Ernie and Big Bird, they had energies in the petaelectronvolt range, thousands of times more energetic than those produced by Earth’s most advanced particle colliders. And three years later, the collaboration made the 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 called the “Texas event.”

Subsequent observations suggested that the source was a “blazar”, a violent galaxy harboring a supermassive black hole at its heart, which can glow brightly. Studies from a series of telescopes observing the blazar using different methods described the source in seven papers in 2018.

“An undisputed force”

Halzen was born in Tienen in Belgium in 1944 and studied at the University of Louvain in Ottignies-Louvain-la-Neuve. He trained as a particle physicist and worked at CERN, the European particle physics laboratory near Geneva, Switzerland, before moving to Wisconsin in 1971.