In a lab buried under the Italy’s Gran Sasso mountain, physicists have observed elusive particles that confirm how the Sun shines. The particles are low-energy neutrinos, which are born of nuclear reactions in the center of stars. Those reactions are responsible for 99 percent of our Sun’s energy.
Neutrinos are tricky to detect because although about 100 trillion of them stream through our bodies every second at nearly the speed of light, they typically slip through the spaces in ordinary matter without a trace. Also, they are have no electric charge. These qualities have earned them the nickname "ghost particles."
Researcher have managed to detect some flavors of neutrinos—ones produced by fusion between two helium atoms—but they haven’t seen the neutrinos produced by the first step of solar nuclear reactions. In that step, one proton (the positively charged subatomic particle in the nucleus of an atom) fuses with another. Neutrinos are a byproduct of that fusion.
An international team of researchers finally detected those proton-proton neutrinos using the Borexino detector housed at the Laboratori Nazionali del Gran Sasso near L’Aquila, Italy. They published their findings Thursday in the journal Nature.
Neutrinos created by the reactions in the heart of the Sun are extremely low energy, so their signature can be masked by cosmic rays and even the low levels of radioactivity in Earth’s soils. Borexino is nearly a mile (1.4 kilometers) under rock in an attempt to shield the detector from anything other than neutrinos.
The finding is the most direct evidence supporting researchers’ ideas about how the Sun is powered. The next step is to look even closer at these ghostly particles for any unexpected qualities that may reveal new physics.
That will require further purifying the liquid at the core of the Borexino detector. That liquid, "already is by far the cleanest mass of liquid that we know of," says Andrea Pocar, a physicist at the University of Massachusetts at Amherst and one of the researchers involved in the new work, in an article from The Christian Science Monitor. "It's a really challenging task."