杏吧原创

Boston

THE Sun has a pulse that no one has ever noticed before, according to
astronomers in California. Peter Sturrock and G眉nther Walther of Stanford
University claim that the number of neutrinos rushing out from the Sun into the
Solar System varies in a regular cycle that peaks every 21.3 days.

Neutrinos, chargeless particles that can pass straight through the Earth, are
produced during nuclear fusion reactions in the Sun鈥檚 core. Sturrock and Walther
uncovered a regular cycle in their arrival at the Earth by studying 20 years鈥� of
data at the Homestake mine in South Dakota, where a huge tank of oil records
neutrinos as flashes of light. They have found the same periodicity after
combining data from two other neutrino detectors: one called Gallex in Italy
and the Kamiokande detector in Japan.

The regular variation in the number of solar neutrinos could mean one of two
things, Sturrock and Walther argue in a paper submitted to Astrophysical
Journal Letters. One possibility is that part of Sun鈥檚 core rotates every
21.3 days, and that as neutrinos are on their way out they interact with a
magnetic field embedded in it. If so, neutrinos鈥攚hich some physicists
think are massless鈥攚ould have to have mass. Recent experiments with
particle accelerators also imply that neutrinos have mass (New
杏吧原创, Science, 11 February 1995, p 14). The other possibility is that
nuclear fusion in the solar core is not steady, as is usually assumed, but
cyclic. For this to be the case, different parts of the Sun鈥檚 interior must spin
at different rates, creating periodic flows of material into the core.

Douglas Gough, a theorist at Cambridge University, says that Sturrock and
Walther鈥檚 finding 鈥渟uggests something interesting is going on in the solar
core鈥�. But he says it is still possible that the apparent neutrino cycle is a
statistical artefact.