Quote:
Originally Posted by Spaceman Spiff
So nature makes such forms of matter, but neutrinos aren't on top of the list of candidates for dark matter because (a) the sum of their rest masses (3 flavors) is fairly well constrained to be < 1 eV, and (b) being nearly massless they are "hot", in that they move at speeds approaching c.
However, in that last regard, what about the neutrinos in the cosmic neutrino background left over from the leptonogenesis in the first 3 seconds of the hot big bang? Are they, too, still hot? Anybody (Ken G?) know about these?
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I don't know much about them, but I am told that such neutrinos are indeed numerous but would not amount to a significant total mass, and would indeed be very "hot" (i.e., too relativistic to form galaxies).