Solar Neutrinos

Aside from nuclear reactors, another powerful source of neutrinos is the sun. Beta decay processes and neutrino emission are intimately associated with the nuclear reactions that power the sun. As a result neutrinos emerge from the small hot core at the center of the sun where the nuclear reactions are taking place. The sun produces so many neutrinos that we can detect them here on earth.

There is a good reason to look for these solar neutrinos. The neutrinos created in the core of the sun pass directly through the outer layers of the sun and reach us eight minutes after they were created in a nuclear reaction. In contrast, light from the hot bright core of the sun takes the order of 14,000 years to diffuse its way out to the surface of the sun. If for some reason the nuclear reactions in the sun slowed down and the core cooled, it would be about 14,000 years before the surface of the sun cooled. But the decrease in neutrinos could be detected here on earth within 8 minutes. Looking at the solar neutrinos provides a way of looking at the future of the sun 14,000 years from now.
Solar neutrinos have been studied and counted since the 1960s. Computer models of the nuclear reactions taking place in the sun make explicit predictions about how many neutrinos should be emitted. The neutrino detectors observe only about 1/3 to 1/2 that number. There have been a number of experiments using various kinds of detectors, and all the experiments show this deficiency.
If the deficiency is really an indication that the nuclear reactions in the sun’s core have slowed, then we can expect a cooling of the sun within 14,000 years, a cooling that might have a significant impact on the earth’s climate. On the other hand there may be some part of the nuclear reactions in the sun that we do not fully understand, with the result that the computer predictions are in error. We are not sure yet which is correct; the solar neutrino deficiency is one of the current areas of active research.