Stockholm: Belgian American physicist Francis Halzen has won 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 Royal Swedish Academy of Sciences announced the award in Stockholm on Tuesday, recognising Halzen's decisive contributions to the development of the huge neutrino observatory built deep beneath the ice at the South Pole in Antarctica.
Halzen, 82, is a professor of physics at the University of Wisconsin Madison and the principal investigator of the IceCube Neutrino Observatory. He proposed using the clear ice of Antarctica as a giant detector for neutrinos in 1988.
Neutrinos are tiny particles with very small masses and no electric charge. They interact only very weakly with matter, allowing huge numbers of them to pass through the Earth and other material without being stopped. Because of this unusual property, scientists have difficulty detecting them but can also use them to study some of the most powerful events in the universe.
IceCube was designed to detect these rare interactions. The observatory uses about 5,160 optical sensors placed deep inside roughly one cubic kilometre of Antarctic ice. The sensors are installed between about 1,450 metres and 2,450 metres below the surface.
When a neutrino interacts with matter in the ice, it can produce charged particles that create a small flash of light. IceCube's sensors record these flashes, allowing scientists to study the direction and energy of the incoming neutrinos.
The project was completed around 2011 after years of construction at the South Pole. Its work produced a major breakthrough in 2013, when scientists reported the first evidence of high energy neutrinos originating beyond the solar system.
The IceCube discovery opened a new way of studying the universe. Unlike light, neutrinos can travel across enormous distances without being significantly absorbed or deflected. Since they carry information from the environments where they were produced, scientists can use them to investigate distant and extremely energetic cosmic events.
In later years, IceCube also helped scientists identify possible cosmic sources of high energy neutrinos, including an active galaxy and the Milky Way. These findings have strengthened the use of neutrinos as a new way to study the universe.
The observatory has also recently undergone its first significant expansion since its completion, keeping the project at the centre of continuing neutrino research.
Halzen said the Nobel award came as a surprise and acknowledged the wider scientific community involved in the IceCube project.
IceCube is an international scientific collaboration involving researchers from institutions around the world, whose work has been essential to the observatory's development and operation.
The discovery of high energy neutrinos has given scientists a new way to investigate some of the universe's most energetic processes. Unlike charged cosmic rays, neutrinos are not deflected by magnetic fields, allowing scientists to trace their arrival directions back toward possible sources.
Scientists still have many questions about where high energy neutrinos come from and what physical processes produce them. Researchers are continuing to use IceCube and other observatories to identify more sources and understand the extreme conditions in which these particles are created.
The 2026 Nobel Prize in Physics carries an award of 12 million Swedish kronor. The Nobel Prize ceremony will be held in Stockholm on December 10.
Halzen's award has brought renewed international attention to IceCube and the continuing effort to understand high energy neutrinos and their sources.