A giant
underground experiment has given researchers their first glimpse into the heart
of the sun and the subatomic particles that shine down on Earth everyday.
Scientists
have long theorized how these particles, called neutrinos,
are formed in the solar inferno, but direct proof has been hard to come by.
Neutrinos can give scientists a priceless glimpse into the inner workings of
the sun because they arrive on Earth virtually unchanged from when they left
the sun's interior.
Princeton
researchers, working at the underground Gran Sasso National Laboratory in Italy,
have made the first real-time observations of low-energy solar neutrinos, fundamental
particles that are created by the roiling nuclear reactions inside the sun and that
stream in vast numbers from the sun's core.
In stars about
the size of the sun, most solar energy
is produced by a complex chain of nuclear reactions that convert hydrogen into
helium. These reactions can take several different routes, but they all end in
the same product: sunshine.
Steps along
two of the 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.
Until now,
technological limitations have made it hard to
detect neutrinos because they rarely interact with other forms of matter.
The Gran
Sasso lab's huge Borexino detector, located more than 0.62 miles (1 kilometer) underground,
overcame the limitations and observed the low-energy neutrinos. The results confirmed
the two nuclear steps that involve beryllium, showing that physicists
have been on target at least about those routes to neutrinos.
However, that
confirmation makes scientists more certain that they are also correct about how
the other processes that create sunlight work, said Princeton physicist Frank
Calaprice, principal investigator of the team.
"Our
observations essentially confirm that we understand how the sun shines," Calaprice
said. "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."
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