16.4 The solar interior: observations  (Page 5/21)

The Borexino experiment , an international experiment conducted in Italy, detected neutrinos coming from the Sun that were identified as coming from different reactions. Whereas the p-p chain is the reaction producing most of the Sun’s energy, it is not the only nuclear reaction occurring in the Sun’s core. There are side reactions involving nuclei of such elements as beryllium and boron. By probing the number of neutrinos that come from each reaction, the Borexino experiment has helped us confirm in detail our understanding of nuclear fusion in the Sun. In 2014, the Borexino experiment also identified neutrinos that were produced by the first step in the p-p chain, confirming the models of solar astronomers.

It’s amazing that a series of experiments that began with enough cleaning fluid to fill a swimming pool brought down the shafts of an old gold mine is now teaching us about the energy source of the Sun and the properties of matter! This is a good example of how experiments in astronomy and physics, coupled with the best theoretical models we can devise, continue to lead to fundamental changes in our understanding of nature.

Key concepts and summary

Studies of solar oscillations (helioseismology) and neutrinos can provide observational data about the Sun’s interior. The technique of helioseismology has so far shown that the composition of the interior is much like that of the surface (except in the core, where some of the original hydrogen has been converted into helium), and that the convection zone extends about 30% of the way from the Sun’s surface to its center. Helioseismology can also detect active regions on the far side of the Sun and provide better predictions of solar storms that may affect Earth. Neutrinos from the Sun call tell us about what is happening in the solar interior. A recent experiment has shown that solar models do predict accurately the number of electron neutrinos produced by nuclear reactions in the core of the Sun. However, two-thirds of these neutrinos are converted into different types of neutrinos during their long journey from the Sun to Earth, a result that also indicates that neutrinos are not massless particles.

For further exploration

Articles

Harvey, J. et al. “GONG: To See Inside Our Sun.” Sky&Telescope (November 1987): 470.

Hathaway, D. “Journey to the Heart of the Sun.” Astronomy (January 1995): 38.

Kennedy, J. “GONG: Probing the Sun’s Hidden Heart.” Sky&Telescope (October 1996): 20. A discussion on hydroseismology.

LoPresto, J. “Looking Inside the Sun.” Astronomy (March 1989): 20. A discussion on hydroseismology.

McDonald, A. et al. “Solving the Solar Neutrino Problem.” Scientific American (April 2003): 40. A discussion on how underground experiments with neutrino detectors helped explain the seeming absence of neutrinos from the Sun.

Trefil, J. “How Stars Shine.” Astronomy (January 1998): 56.

Websites

Albert Einstein Online: http://www.westegg.com/einstein/.

Ghost Particle: http://www.pbs.org/wgbh/nova/neutrino/.

GONG Project Site: http://gong.nso.edu/.