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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
http://xxx.lanl.gov/abs/hep-ph/9503430 ). 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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