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Out of this world: winners of this year's physics Nobel, (from left) Raymond Davis, Masatoshi Koshiba and Riccardo Giacconi. Credit: BROOKHAVEN NATL LAB.; AP/KYODO

Three pioneers who together opened a new window on the Universe have this year been rewarded with the Nobel physics prize.

Raymond Davis of the University of Pennsylvania in Philadelphia and Masatoshi Koshiba of the University of Tokyo share half the prize for developing techniques to detect the dauntingly elusive subatomic particles called cosmic neutrinos.

The other half of the award goes to Riccardo Giacconi for his role in building the first instrument for detecting X-rays from cosmic sources. Giacconi is now president of Associated Universities Incorporated, a Washington-based consortium that runs the National Radio Astronomy Observatory for the US National Science Foundation.

Davis set up an audacious experiment in the 1960s to detect neutrinos coming from the Sun. Solar theories had predicted that nuclear fusion reactions at the Sun's heart would generate vast numbers of neutrinos. But the particles rarely interact with matter, so it was unclear whether they could be detected.

To catch the solar neutrinos, Davis directed the construction of a detector at the Homestake gold mine in South Dakota, where a tank was filled with 615 tonnes of the cleaning fluid tetrachloroethylene. He calculated that a tiny proportion of the neutrinos would have enough energy to collide with chlorine atoms in the fluid, creating argon atoms in the process. About 20 argon atoms were expected to be created every month, and Davis devised a method of extracting them by pumping helium gas through the liquid. By the time it closed in 1994, the experiment had detected about 2,000 argon atoms.

Koshiba followed up this work in the 1980s, leading a team that built a neutrino detector known as Kamiokande. Housed in a mine roughly 240 kilometres northwest of Tokyo, Kamiokande monitored the light produced by neutrinos when they collided with water molecules, allowing it to identify when the particles arrived and which direction they were moving in. Koshiba's team showed conclusively that the Sun emits neutrinos.

In February 1987, the group also detected a neutrino burst from a supernova explosion in a neighbouring galaxy, showing that neutrino detectors could be used to study distant astronomical objects.

Koshiba's award is the third to go to Japan in as many years, keeping the country on track for the government's stated aim, set out in 2000, to try to win 30 Nobel prizes within 50 years. “My dream now is that one of my students can also get a Nobel prize,” says Koshiba.

Giacconi began working on X-ray astronomy in the late 1950s and helped to launch a field that has transformed our view of the Universe. Previously, astronomers had relied on optical, infrared and radio frequencies, but X-rays revealed violent astrophysical processes that no one had expected. “X-rays show us the extreme end of things,” says Martin Ward of the University of Leicester, UK. Giacconi's award is “very well deserved for half a century of work in this area”, he adds.

X-rays are absorbed by the Earth's atmosphere, so Giacconi's team developed instruments to detect them from rockets. Their initial aim was to see whether solar radiation caused X-ray emission from the Moon, but once beyond the atmosphere, their detector revealed other X-ray sources such as that in the constellation of Scorpius.

Strikingly, all three prizewinners have been recognized largely for their work on instrumentation — an acknowledgement, perhaps, that many questions in high-energy astrophysics cannot even be framed until observational methods exist.

Additional reporting by David Cyranoski.

The Nobel chemistry prize was announced after Nature went to press. For coverage see → http://www.nature.com/nature