For the first time in the history of solar research, scientists have successfully measured the Sun’s energy at the instant it’s created, thanks to improved technology that enables detection of solar neutrinos.
Our Sun’s core holds a temperature of a whopping 15 million degrees Celsius and is home to various fusion reactions, releasing the energy that creates sunshine (solar radiation). Ninety nine per cent of this energy is created in a fusion cycle that starts with two hydrogen atoms fusing into a single atomic nucleus of heavy hydrogen. The reaction also creates electrically neutral particles called neutrinos.
In the Italian Gran Sasso underground laboratory, physicists of the Borexino Collaboration are for the first time directly observing these neutrinos, as reported in the latest issue of the journal Nature.
Sunshine: more than a hundred thousand years in the making
Previous analyses of the Sun’s energy built on measurements of solar radiation. On average, this radiation takes more than one hundred thousand years to travel from the Sun’s dense core to its surface.
“While the light we see from the Sun in our daily life reaches us in about eight minutes, it takes tens of thousands of years for energy radiating from the Sun’s centre to be emitted as light,” says physicist Andrea Pocar in a press release from University of Massachusetts. Pocar is one of more than 100 scientists behind the new study.
This means the previously calculated values correspond to the energy that was released over a hundred thousand years ago inside the Sun.
Neutrinos offer a glimpse into ‘the Sun’s soul’
Neutrinos behave in a completely different manner. As electrically neutral elementary particles, neutrinos hardly interact with other matter, allowing them to move freely. They leave the Sun’s core within seconds of their creation and reach the Earth in only eight seconds – more or less at the speed of light.
“By comparing the two different types of solar energy radiated, as neutrinos and as surface light, we obtain experimental information about the Sun’s thermodynamic equilibrium over about a 100,000-year timescale,” Pocar adds. “If the eyes are the mirror of the soul, with these neutrinos, we are looking not just at its face, but directly into its core. We have glimpsed the Sun’s soul.”
The results provide the first experimental proof that the energy released from the Sun has remained unchanged for a very long time.
What’s the Borexino?
The Borexino instrument is installed in the Italian Gran Sasso underground laboratory approximately 1400 meters beneath the surface of the Earth.
It’s used to detect neutrinos as they interact with the electrons of an ultra-pure organic liquid scintillator at the center of a large sphere surrounded by 1,000 tons of water.
The Borexino Collaboration involves scientists from Italy, Germany, France, Poland, USA and Russia.
Borexino: the world’s most sensitive detector
However, the same properties that enable the neutrinos’ speedy escape from the Sun also make these particles extremely difficult to measure.
“The published observation was possible only because Borexino is the most sensitive detector worldwide and we were able to massively reduce noise from radiation and other cosmic particles,” says Stefan Schönert from the Technische Universität München (TUM), who co-authored the study.
“In addition to solar neutrinos, we can also observe neutrinos from the interior of the Earth and use them to test geophysical models,” adds Lothar Oberauer, another TUM physicist involved in the work.
The scientists of the Borexino Collaboration have further ambitious plans. In the next four years they hope to improve the previously made measurements and to make new observations of neutrino particles. In particular, they are gearing up for a search for so-called sterile neutrinos. Their existence would have fundamental repercussions for particle physics, astrophysics and cosmology.