Il Nuovo Postiglione - Nobel physics prize hails 'ghostly messengers' from space

"This year's prize is about ghostly messengers from space," Ellen Moons, secretary general of the Royal Swedish Academy of Sciences, told a news conference.

Halzen was honoured "for decisive contributions to the IceCube Neutrino Observatory and the discovery of high-energy neutrinos of astrophysical origin", the jury said.

The Royal Swedish Academy of Sciences said Halzen's work had been fundamental for the observatory, which consists of a cubic kilometre of ice that is equipped with light sensors, and had "paved the way for a new kind of astronomy".

Using the observatory, researchers can capture neutrinos -- rare subatomic particles -- "from extremely energy-rich processes in the distant universe".

Halzen, 82, was born in Tienen, Belgium and is a professor at the University of Wisconsin–Madison in the United States, where he is a citizen.

"It was a great surprise, and I obviously didn't expect it," he told the news conference by telephone shortly after the prize was announced.

- 'The instigator' -

"Unlike other particles, neutrinos reach us without changing direction or losing energy. This means they can provide information that is not available in any other way," the academy said in a statement.

"Cosmic neutrinos with extremely high energies are very rare, so an enormous volume of ice is needed to observe an adequate number of collisions," the jury explained.

Halzen first presented his idea for the observatory in 1988 and it quickly gained the support of other researchers.

Preliminary testing was conducted just a few years later but the observatory was not completed until 2011 and soon discovered the first "high-energy neutrinos."

"For me, the main pleasure of it, besides winning the Nobel Prize, is that I hope this reflects on the really courageous people who joined me in the beginning of this project," Halzen said.

Halzen is the first physics laureate since 1992 who did have to share the honour with other researchers.

But Erin O'Sullivan, a neutrino astrophysicist at Sweden's Uppsala University and spokeswoman for the IceCube collaboration, said it was "well deserved that he is the sole winner of this prize".

"He really was the instigator of this whole project and has seen it through since the very early days," O'Sullivan told AFP.

In an interview with the Nobel Foundation, Halzen expressed how thankful he was that the project had received support even early on.

"This project, everybody thought, is a cute idea that won't work," Halzen said.

Belgium's Prime Minister Bart De Wever extended his "heartfelt congratulations" to Halzen, noting that he was the 11th Belgian to win a Nobel, and the second in physics.

"An impressive recognition of a life dedicated to unravelling the greatest secrets of the cosmos through its most minuscule manifestations," De Wever said in a post on X.

- Alien speculation -

Asked whether these neutrinos could contain messages from potential distant civilisations, Halzen admitted that "it has been speculated that... this would be an ideal way to communicate with aliens."

"But I don't think I will go there. I think we have enough realistic problems to deal with right now," he said.

The award is the second Nobel of the season, after the medicine prize was awarded on Monday to US psychiatrist and neurologist Karl Deisseroth and German scientists Peter Hegemann and Georg Nagel.

The researchers were honoured for their pioneering work in the field of optogenetics, which involves controlling nerve signals with light.

Last year, the Nobel Prize in Physics went to Briton John Clarke, Frenchman Michel Devoret and American John Martinis for putting quantum mechanics into action and enabling the development of all kinds of digital technology from cellphones to a new generation of computers.

The physics prize will be followed by the chemistry one on Wednesday.

The literature laureate will be revealed on Thursday. Perhaps the most keenly anticipated award -- the peace prize -- is due on Friday.

The economics prize wraps up the Nobel season on October 12.

E.Danieli--INP