Scientists have long believed that the power of the sun comes largely from the fusion of protons into helium, but now they can finally prove it. An international team of researchers using a detector buried deep below the mountains of central Italy has detected neutrinos—ghostly particles that interact only very reluctantly with matter—streaming from the heart of the sun. Other solar neutrinos have been detected before, but these particular ones come from the key proton-proton fusion reaction that is the first part of a chain of reactions that provides 99% of the sun’s power.
The results also show that the sun is a remarkably steady power source. Neutrinos take only 8 minutes to get from the sun’s core to Earth, so the rate of neutrino production that the team detected reflects the amount of heat the sun is producing today. It just so happens that this is the same as the amount of energy now being radiated from the sun’s surface, even though those photons have taken 100,000 years to work their way from the core to the surface. Hence, the sun’s energy production hasn’t changed in 100 millennia. 'This is direct proof of the stability of the sun over the past 100,000 years or so,' says team member Andrea Pocar of the University of Massachusetts, Amherst.
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