That one had me stumped, so here's what some more knowledgeable colleagues wrote:
"It is true that massive neutrinos can, in principle, be captured by stars (not by small objects like people). However, this would only happen to neutrinos having energies more than a million times lower than the typical energies of cosmic neutrinos.
High energy neutrinos interact much more easily than the low energy ones, so it is unlikely that an accumulation of low energy neutrinos (in the Sun, for example) would have an observable effect.
More advanced: Neutrinos can initiate some nuclear decays in a way that is similar to those initiated by electrons in certain nuclei.
The electron process is called, not surprisingly, "electron capture".
Electron capture depends on the fact that the electron is tightly bound to the nucleus by electric force. Lacking a similar binding force, the corresponding neutrino process would be extremely rare.
The neutrino capture mechanism I had in mind is gravity. Because neutrinos don't have strong or EM interactions, that's the only method. ==> why only very massive objects can capture (slowly moving) neutrinos.
Very Technical point:
The capture cross section is very small, because capture requires an inelastic scatter with the star. This is only significant in very dense objects, like neutron stars. The sun is nearly transparent to neutrinos."
"I liked this question. While we can't collect them,
Brian Fields worked on earth tomography with neutrinos,
maybe you can offer this comment as a prize to the person who submitted the question? http://www.astro.uiuc.edu/~bdfields/geoneutrinos.html
I hope that helps a bit. (Thanks to Jon and Inga)
(published on 01/31/09)