Explainer: How does our sun shine?

Aug 28, 2014 by Brad Carter
The dawn of a new day. Credit: Flickr/Christos Tsoumplekas, CC BY-NC

What makes our sun shine has been a mystery for most of human history. Given our sun is a star and stars are suns, explaining the source of the sun's energy would help us understand why stars shine.

An early explanation offered as to why the shines came from the Greek philosopher Anaxagoras. In around 450 BCE he taught that the sun shines because it is a "red-hot" stone.

During the mid-19th century, German physician Julius Mayer estimated that if the sun were a giant lump of burning coal it could only shine for some thousands of years. Thus it became generally appreciated that any form of chemical combustion was insufficient.

Both Mayer and Scottish hydrographer John Waterston speculated that the sun was powered by the release of gravitational energy from impacting meteorites.

Waterston also suggested that the could instead come from a slow contraction of the sun. This idea is now discounted for the sun today, but is the means by which all stars can shine when they are forming.

Later in the 19th century the renowned physicists Lord Kelvin and Hermann von Helmholtz pursued the idea of gravitational contraction. But the problem remained that the sun could only shine this way for some tens of millions of years.

This is a small fraction of the age of the Earth as then estimated from geological studies, and increasingly discrepant as Earth's estimated age was revised upwards.

The atomic age

The situation changed in the early 20th century with the advent of so-called "modern physics" that began to understand the structure and behaviour of atoms. This included Albert Einstein's work equating mass with energy.

So while some suggested radioactive decay as the source of the sun's energy the relative absence of the atoms needed was against this explanation.

Instead, we turn to the work of the British physicist and chemist Francis Aston who showed that four hydrogen atoms have more mass than a helium atom. This led the British astrophysicist Arthur Eddington to propose that the conversion of the sun's hydrogen atoms into helium. The resulting conversion of matter to energy could keeping the sun shining for many billions of years.

Following Eddington's insight it took years for a theory to be developed as to how the collision of hydrogen atoms inside the sun and other stars makes hydrogen atoms and release energy.

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Due to the work of scientists such as George Gamow, Robert Atkinson, Fritz Houtermans, Edward Teller, and then Carl von Weizsacker and Hans Bethe, by the eve of the second world war the theory eventually became clear.

Hydrogen fusion inside the sun and other stars is a multi-step process, and involves a series of collisions of two atoms together, rather than the improbable collision of three or even four atoms together as a single event.

In addition, stars generate energy by the fusion of into helium into two ways. Inside stars more massive than the sun, the dominant process is a "CNO cycle" that also involves atoms of carbon, nitrogen and oxygen. But for stars such as our sun, the dominant process is the "proton-proton" chain reaction.

Where's the evidence?

In science, theories produce predictions that are subject to testing via experiment and observation, and the proton-proton chain predicts that subatomic particles called neutrinos will flood outwards from the sun and be detectable here on Earth.

But are particles that are difficult to observe as they only weakly interact with matter. Most pass unhindered through our bodies and the entire bulk of the Earth.

Nevertheless, it is possible to construct a , using a large underground fluid-filled chamber in which neutrinos are detected as occasional flashes of light from a collision of a neutrino with the atoms in the fluid.

When various teams started observing solar neutrinos from the 1960s onwards they were greatly surprised to detect fewer solar neutrinos than predicted, by a factor of two or three. What was going wrong? Was a new theory needed?

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The solution to the solar neutrino mystery was to be found through the suggestion of Vladimir Gribov and Bruno Pontecorvo. They found that solar neutrinos oscillate between between different states that were not all being detected by the existing neutrino observatories.

Work done at the so-called Super-Kamiokande neutrino observatory in Japan resulted in the detection of these oscillations in the 1990s. This supported our basic picture of the sun as a hydrogen fusion reactor with the proton-proton chain reaction ultimately powering the sunlight we all take for granted.

Despite the scientific advances made over the years, the key initial step in the process of inside the sun has lacked direct observational evidence. Until now.

Plenty of sun light was reaching Earth but where were the neutrinos to prove the theory? Flickr/Julie Falk , CC BY-NC

A new discovery

A team from the Borexino neutrino observatory in Italy have announced, in a research paper published in Nature today, the detection of low-energy neutrinos produced in the nuclear reaction that initiates generation.

This finding is significant as these so-called "pp neutrinos" constitute the overwhelming majority of neutrinos produced inside the sun. It demonstrates that 99% of the sun's power indeed results from the proton-proton .

Science has thus made clearer the nature of solar energy generation, and supporting the general picture of stars as factories that transmute one element to another.

Inside the Borexino stainless steel sphere showing some of the photomultipliers used to detect the pp neutrino. Borexino Collaboration

The physics of what makes our sun and stars shine informs our understanding of the origins of our solar system, our planet and ourselves. As the astronomer Carl Sagan would say, we are all "star-stuff".

While the Big Bang made the hydrogen and helium that is abundant in the universe, stars have essentially produced the remainder of the periodic table. They made the atoms that are today part of our planet and ourselves.

So the latest insight provided by the Borexino Collaboration about our sun is another step in the long but now detailed path that science has illuminated between the beginning of our universe and our present moment in time here on Earth.

Explore further: Detecting neutrinos, physicists look into the heart of the Sun

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User comments : 5

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mikep608
1 / 5 (8) Aug 28, 2014
THE SUN DOESN'T REALLY SHINE. WE JUST SEE IT THAT WAY. TO THE SUN, THIS IS JUST NORMAL AND MECHANICAL. HERE'S MY WEBPAGE LINK. I LIKE TO REINTERPRET EXPERIMENTAL RESULTS SO WE CAN HAVE MORE USEFUL KNOWLEDGE TO GUIDE US IN PROGRESS.https://www.faceb...eline
mikep608
1 / 5 (8) Aug 28, 2014
HERE'S MY WEBPAGE LINK. I LIKE TO REINTERPRET EXPERIMENTAL RESULTS SO WE CAN HAVE MORE USEFUL KNOWLEDGE TO GUIDE US IN PROGRESS

https://www.faceb...timeline
mikep608
1 / 5 (8) Aug 28, 2014
POP UP NEUTRINOS AND OTHER VIRTUAL PARTICLES THAT DECAY RAPIDLY IS JUST A PROTONS FREQUENCY CREATING A REACTION WITH AETHER IN THE FORM OF EMR.JUST LIKE PHOTONS THEY ARE NOT PARTICLES.THIS SHOULD BE EXPECTED BECAUSE THE NUCLEAR FUSION AND FISSION HAPPENING ARE AFFECTING THE PROTON'S FREQUENCY. (I BET)
Jixo
1 / 5 (2) Aug 28, 2014
According to the so-called Standard Solar Model, nuclear fusion reactions at the sun's center pump out vast quantities of energy. About 2 percent of that energy should appear in the form of neutrinos - fundamental particles that interact only weakly with matter. But that's not what researchers see. Data collected by an Earth-based Homestake detectors over a period of 20 years suggest that the neutrino flow from the sun varies from time to time rather than remaining constant. Moreover, the flux seems to follow a pattern that runs counter to the rise and fall in the number of sunspots visible on the sun's surface. This time variation of the neutrino flux coincides with the well-known 11-year cycle of solar activity, which further coincides well with the orbital period of Jupiter planet. The neutrino flux is high when solar activity is low and declines to near-zero values as the number of sunspots rises to a peak.
Jixo
1 / 5 (2) Aug 28, 2014
Waterston also suggested that the gravitational energy could instead come from a slow contraction of the sun. This idea is now discounted for the sun today, but is the means by which all stars can shine when they are forming.
Well, this mechanism still applies in certain sense, but what is shrinking in average are the atom nuclei inside of Sun, not the Sun as such. In this way, the density of particles inside of the Sun still gets more dense in average, but their increasing temperature and speed of their collisions wipes out the effect of the internal shrinking of atoms from outside perspective.

The similar process happens during decay of social groups like the political parties or multilevel marketing companies. At the their spontaneous beginning they're all formed with many closely attached but poor activists, but as their leading members become fat and corrupted, the group is losing its wide membership base as a whole and the people become more individualist there.