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The Question

(Submitted January 20, 1998)

I have heard that neutrinos are responsible for a large amount of energy transfer out of stellar cores. I have also heard that neutrinos sometimes "carry" photons with them. How does this phenomena occur? I have a B.S. in Physics with some formal exposure to astronomy and particle physics.

The Answer

In our Sun, 98% of the energy is produced by the chain of reactions which produce a helium nucleus from 4 protons. This process produces a couple of neutrinos with typical energies of a few hundred keV. Total predicted neutrino energy flux is about 10-20 W/m^2 at the distance of Earth, or about 1% of the sunlight flux. (These numbers are loosely derived from tables and graphs in ). Note that theory and experimental measurements seem to disagree with each other by a factor of ~3 in this field.

However, some stars are much more neutrino-oriented. In the final stages before the core collapse leading to a supernova, a massive star burns 1.4 solar masses of silicon into iron in about 2 DAYS. The power produced is 10,000,000 as much as it was during its hydrogen-burning main-sequence life (when it was an immensely bright blue or red supergiant), but 99.99998% of that power is ghosted away as neutrinos. The core collapse supernova itself releases 99% of its energy as neutrinos.

I have never heard of neutrinos carrying photons with them.

David Palmer
for Ask an Astrophysicist

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