For the first time in the scientific inquiry of a star, our Sun, measurement of the stellar power at the moment of its production has been achieved by the Borexino collaboration which announced their results in an article published today by the prestigious, interdisciplinary, scientific journal Nature.
This very important achievement was obtained by detecting solar neutrinos, which are produced by nuclear reactions deep within the Sun, and which then pass right through the Sun, taking just over eight minutes to reach the Earth. Until now, all solar energy measurements were based on light from the Sun's photosphere - the familiar sunlight which lights up our skies and warms the Earth. But the energy carried by this sunlight was produced in solar fusion reactions about 100,000 years ago – the average time for energy to percolate from the central regions of the Sun and reach its surface.
Comparison between the Borexino measurement and those of the Sun's radiant energy reveals that the solar power has not changed in quite a long time.
The Borexino detector, installed in the underground Gran Sasso Laboratory of the Italian National Institute of Nuclear Physics (I.N.F.N.), measured the flux of neutrinos produced in the Sun by the fusion reaction of two hydrogen nuclei to form a nucleus of deuterium.This is the seed reaction of the nuclear fusion cycle which produces about 99% of the solar energy.
Before this, Borexino had already measured neutrinos from subsequent nuclear reactions, but these contribute much less to solar energy production. (Yet they are themselves key to understanding basic properties of this evanescent member of the elementary particles, the neutrino.)
The very nature of neutrinos which allows them to escape from the center of the Sun makes them exceedingly hard to detect here on Earth, requiring very large detectors for even a few events. Measuring pp neutrinos was made even more difficult due to their very low energy, actually the lowest among solar neutrinos, which placed them well below major natural backgrounds. Borexino achieved the amazingly low background required, and alone has the capability to perform such a measurement. Borexino is indeed unique in the world, and will remain so for many years, thanks to the advanced technology used in its construction, which allows it to study not only the neutrinos emitted by the Sun, but also those produced from our Earth, and even man-made sources.
The Borexino experiment is a joint collaboration of several European (Italy, Germany, France, Poland), USA and Russian institutions and will take data for at least four more years, improving the accuracy of the results already achieved, and has plans to concurrently address other very important problems in the fields of particle physics, astro-particle physics and astrophysics. The result is obtained with an active participation of DLNP JINR scientists.