THE Sun pelts Earth with far fewer electron neutrinos than most models of
solar structure predict. That fact has left scientists with a dilemma known as
the solar neutrino problem. Either the standard physics used to model the
structure of the Sun is wrong, or the physicists who think they know how
neutrinos behave are wrong.
Now a detailed study of waves on the star鈥檚 surface has revealed almost
perfect agreement with models of the Sun鈥檚 structure. The standard physical
description of the Sun seems to be safe. It is the particle physicists and their
ideas about neutrinos who need to revisit the drawing board.
The temperature at the Sun鈥檚 core is an important piece of the solar neutrino
puzzle. The core would generate electron neutrinos at the detected
rate鈥攁bout one-third of that predicted by models鈥攊f it was even 10
per cent cooler than physicists believe. But physicists cannot directly measure
core temperature to that accuracy.
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Instead, John Bahcall of the Institute for Advanced Study in Princeton, New
Jersey, and colleagues elsewhere in the US and in Denmark used new measurements
of the waves that appear on the Sun鈥檚 surface. The team determined, based on the
waves鈥� trajectories, which of these would pass through the core of the Sun.
These revealed its temperature and structure rather as details of the interior
of Earth can be gleaned by studying how earthquake waves pass through it. Their
observations match the standard solar model to an accuracy better than 0.2 per
cent (Physical Review Letters, vol 78, p 171). 鈥淚 find the precise
agreement just stunning,鈥� says Bahcall.
This dramatic achievement shows that electron neutrinos must be disappearing
before they hit Earth. Some physicists have already speculated that they might
convert to other flavours of neutrinos鈥攖he muon and tau (鈥淐osmic
changelings鈥�, 快猫短视频, 16 March 1996, p 28).
John Ellis, a particle physicist with CERN, accepts that the next step is up
to those in his discipline. 鈥淭he solar neutrino problem cannot be solved by
tinkering with the standard model of the Sun.鈥�