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Jun14-11, 02:29 PM
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Quote Quote by Islam Hassan View Post
Funny, isn't density a factor at all? I would have thought that the sheer density of matter in a neutron star would significantly raise the probability of impact. After all, if you can precisely align a neutrino's trajectory with a nucleon, wouldn't impact be guaranteed? How would impact depend only on the magnitude of mass encountered and not on its spatial 'packing'?

I'm not sure this part has been answered. A nucleon is complex object (an acquaintance who assisted programming lattice QCD likened it to weather forecasting, only worse), consisting of quarks and gluons (mostly). From the perspective of a neutrino, it is mostly empty space. Thus, first order, squeezing a given mass into a smaller volume does not change the interaction cross section.

Given that it takes light years of lead to reach 50% chance of absorbing a neutrino, that is enough to conclude that neutrons stars have a small chance of stopping a neutrino.