Princeton scientists confirm long-held theory about source of sunshine

Scientists are a step closer to understanding sunshine. A monumental experiment buried deep beneath the mountains of Italy has provided physicists with a clearer understanding of the sun's heart -- and of a mysterious class of subatomic particles born there. The researchers have made the first real-time observation of low-energy solar neutrinos, which are fundamental particles created by nuclear reactions that stream in vast numbers from the sun's core. In stars the size of the sun, most solar energy is produced by a complex chain of nuclear reactions that converts hydrogen into helium. Beginning with protons from hydrogen's nucleus, the chain takes one of several routes that all end with the creation of a helium nucleus and the production of sunlight. Steps along two of these routes require the presence of the element beryllium, and physicists have theorized that these steps are responsible for creating about 10 percent of the sun's neutrinos. But technological limitations had made the theory difficult to test until now.