Scientists confirm long-held sunshine source theory

A joint American-Italian experiment has provided physicists with a clearer understanding of the Suns heart - and of a mysterious class of subatomic particles born there.

Washington, Aug 21 : A joint American-Italian experiment has provided physicists with a clearer understanding of the Sun's heart - and of a mysterious class of subatomic particles born there.

Princeton University researchers, working as part of an international collaboration at the underground Gran Sasso National Laboratory near L'Aquila, Italy, have made the first real-time observation of low-energy solar neutrinos.

These are fundamental particles created by nuclear reactions that stream in vast numbers from the sun's core.

"Our observations essentially confirm that we understand how the sun shines. Physicists have had theories regarding the nuclear reactions within the sun for years, but direct observations have remained elusive. Now we understand these reactions much better," said Frank Calaprice, a professor of physics and principal investigator of the Princeton team.

Prof. Calaprice said the precise measurement of the neutrinos' energy has provided long-sought proof of the theory regarding how these neutrinos are produced.

In stars the size of the Sun, a complex chain of nuclear reactions converts hydrogen into helium to produce most of the solar energy.

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.

Most particles that emerge from the Sun take so long to escape the interior that they change drastically before scientists can study them, so it has been difficult to prove how the sun creates energy.

The Gran Sasso lab's giant Borexino detector, located more than a kilometre below the Earth's surface, overcame these limitations, permitting the team to observe low-energy neutrinos, which interact extremely rarely with other forms of matter.

Neutrinos provide a key because they escape before they have time to change.

"The findings show that science's understanding of the chain of nuclear processes that make the Sun shine is essentially correct, as least as far as the part of the chain that involves beryllium is concerned," said Prof. Calaprice.

"The reaction does not generate a large percentage of the Sun's energy, but confirming that we understand it makes us more certain that we know how the other processes that create sunlight work," he said.

ANI