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Why do neutrons repel each other?

What I mean is that the neutrons are attracted to one another via gravity, so what force keeps them from collapsing to form a "neutron black hole"? Considering that they have no electric charge...

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marked as duplicate by Qmechanic, dmckee Jun 6 '12 at 23:51

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

    
Related: physics.stackexchange.com/q/78/2451 –  Qmechanic Jun 6 '12 at 22:10
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1 Answer 1

It's well explained at wikipedia:

Neutron stars are very hot and are supported against further collapse by quantum degeneracy pressure due to the Pauli exclusion principle. This principle states that no two neutrons (or any other fermionic particles) can occupy the same place and quantum state simultaneously.

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i red it, but i couldn't understand what force is it. i mean is it an actual force that keeps them apart or a quantic phenomenon? or is it the thermal movement... –  lee Jun 6 '12 at 22:22
    
It's a Fermi gas pressure. Similar to air pressure but neutrons here obey quantum Fermi–Dirac statistics unlike air particles for which Boltzmann statistics is more appropriate. –  qoqosz Jun 6 '12 at 22:48
    
@lee It comes from the Pauli Exclusion rule for particles with half-integer spin (called fermions)---they can not occupy identical quantum states---so, yes it is intrinsically quantum mechanical and it is also a "actual" force. –  dmckee Jun 6 '12 at 23:39
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