Nobel Prize rewards neutrino astrophysics and X-ray astronomy

This year's Nobel Prize for Physics has been awarded to three
astrophysicists who pioneered the fields of neutrino astrophysics and
X-ray astronomy. Ray Davis and Masatoshi Koshiba share half the prize for
"pioneering contributions to astrophysics, in particular for the detection
of cosmic neutrinos". Riccardo Giacconi receives the other half of the
prize for "pioneering contributions to astrophysics, which have led to the
discovery of cosmic X-ray sources."

Although vast numbers of neutrinos are produced by the Sun, they are very
difficult to detect because they interact very weakly with matter. Ray
Davis, now at the University of Pennsylvania built the first experiment to
detect neutrinos from the Sun - a giant underground tank containing 600
tonnes of dry-cleaning liquid. However, Davis only detected about one
third of the flux of neutrinos predicted by theory. Masatoshi Koshiba of
the University of Tokyo later built the gigantic Kamiokande detector in
Japan and confirmed Davis's results.

Now it is known that the electron neutrinos produced in the Sun can
oscillate into other types of neutrino - such as muon and tau neutrinos -
that could not be detected by these experiments. Recent experiments, such
as SuperKamiokande in Japan and the Sudbury Neutrino Observatory in
Canada, have confirmed that oscillations do indeed occur. This means that
neutrinos have mass, which requires new physics beyond the Standard Model
of particle physics.

Riccardo Giacconi - the Italian born astronomer who is now head of
Associated Universities Inc in the US - was one of the pioneers of X-ray
astronomy. Since X-rays from the Sun and other sources are absorbed by the
atmosphere, X-ray astronomy can only be carried out from space. Giaconni
was the first astronomer to detect X-rays from outside our solar system
and also the first to prove that the universe contains an X-ray
background. X-ray astronomy is now one of the most active areas of
astrophysics and two large observatories - Chandra and XMM Newton - have
been launched in recent years.

The winners will share the cash prize of 10 million Swedish kroner and
will receive their gold medals and diplomas in Stockholm on 10 December.

See http://physicsweb.org/article/news/6/10/7 for more details.