A multinational collaboration of physicists has directly detected neutrinos created by the proton-proton fusion process going on at the heart of the Sun.
Physicists have directly detected pp neutrinos, demonstrating that about 99 per cent of the power of the Sun is generated by the pp fusion process. Image credit: Nathalia Alzate / SDO.
In the core of the Sun, energy is released through sequences of nuclear reactions that convert hydrogen into helium.
The primary reaction is thought to be the proton-proton (pp) fusion with the emission of a low-energy neutrino.
These so-called pp neutrinos constitute nearly the entirety of the solar neutrino flux and stream out of the Sun at nearly the speed of light.
Although solar neutrinos from secondary processes have been observed, proving the nuclear origin of the Sun’s energy and contributing to the discovery of neutrino oscillations, those from pp fusion have eluded direct detection for decades.
Now, physicists using the Borexino detector – one of the most sensitive neutrino detectors on Earth – have succeeded in detecting pp neutrinos.
“With these data, we are directly looking at the originator of the Sun’s biggest energy producing process, or chain of reactions, going on in its extremely hot, dense core,” said Dr Andrea Pocar of the University of Massachusetts Amherst, who is a member of the Borexino collaboration and a co-author of a paper published in the journal Nature.
“While the light we see from the Sun in our daily life reaches us in about eight minutes, it takes tens of thousands of years for energy radiating from the Sun’s center to be emitted as light.”
Dr Pocar added: “by comparing the two different types of solar energy radiated, as neutrinos and as surface light, we obtain experimental information about the Sun’s thermodynamic equilibrium over about a 100,000-year timescale. If the eyes are the mirror of the soul, with these neutrinos, we are looking not just at its face, but directly into its core.”
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G. Bellini et al. 2014. Neutrinos from the primary proton–proton fusion process in the Sun. Nature 512, 383–386; doi: 10.1038/nature13702
