Cosmic particles scoop Nobel Prize

Raymond Davis Jr and Masatoshi Koshiba take one half of the 10 million kronor award, and Riccardo Giacconi the other half.

Davis Jr, from the University of Pennsylvania, US, and Koshiba, from the University of Tokyo, detected tiny particles called neutrinos from within, and outside, the solar system.

Their insights, and follow-up experiments by other researchers, have enabled science to confirm long-held theories about the nuclear reactions that go on inside the Sun.

Giacconi, a scientist from Washington DC, made instruments capable of detecting x-rays from outside our Solar System.

In a statement, the Royal Swedish Academy of Sciences said: "This year's Nobel laureates in physics have used these very smallest components of the universe to increase our understanding of the very largest: the Sun, stars, galaxies and supernovae.

"The new knowledge has changed the way we look upon the Universe."

Neutrino Find

It was first predicted that the neutrino might exist as early as 1930 - but it was 25 years before its existence could be proven.

The particle is formed during the nuclear fusion reactions at the heart of stars such as our own Sun, in which hydrogen is converted to helium.

But neutrinos are ghostly particles with no electric charge and very little mass. They can pass through millions of kilometres of matter with no effect - though with a 600-tonne detector, Raymond Davis was able to identify some - just 2,000 in total - coming from the Sun.

This provided the proof that nuclear fusion lay at the heart of our star.

Koshiba was able to first repeat this finding and then extended it, when, in February 1987, he managed to detect a tiny number of neutrinos emitted by a distant supernova explosion.

Now the technique has spawned a new branch of astronomy - neutrino astronomy - which is used to study far-distant objects.

X-ray detector

Giacconi paved the way for modern X-ray astronomy, which provides spectacular images of the Universe.

All stars, including the Sun, emit radiation at various wavelengths, including x-ray radiation.

Cosmic x-ray radiation does not get through the Earth's atmosphere, but Giacconi placed instruments in space and, for the first time, detected a source of X-rays outside our own Solar System.

Some of the x-ray sources he detected are now thought to contain black holes.

There are now two major X-ray telescopes in orbit, Chandra and the Newton.

Previous winners

Last year, the physics award went to three scientists for the discovery of the Bose-Einstein condensate, a new state of matter, in 1995.

Americans Eric A Cornell and Carl E Wieman and German scientist Wolfgang Ketterle created this ultra-cold gas that may one day help scientists develop smaller and faster electronic circuitry.

On Monday, Britons Sydney Brenner, 75, and Sir John Sulston, 60, and American H Robert Horvitz, 55, were awarded the Nobel medicine prize, for discoveries relating to the life cycle of cells.