The question is: Suppose the sun collapses into a neutron star. What will its radius be? The question gave a brief backround explaining that stars are powered by nuclear reactions that fuse hydrogen and helium. When the hydrogen is used up the star collapses into a neutron star. The force of gravity becomes so large that protons and electrons are fused into neutrons. The entire star is then a tightly packed ball of neutrons with the density of nuclear matter. I am not even sure how to begin. Any help would be appreciated. Thanks.