I have just attended a talk, where the speaker (a professor in Hong Kong University) claims that neutron stars don't collapse due to "nuclear forces". He further explains that those nuclear forces are residual strong forces (i.e. exchange of pions). However, the mainstream saying (according to Wikipedia) I've heard is that they are sustained by neutron degeneracy forces. Which is correct? And if it is indeed sustained by nuclear force, how does it work since as far as I know, nuclear forces are attractive.