Under some circumstances, a star can collapse into an extremely dense object made mostly of neutrons and called a neutron star. The density of a neutron star is roughly $10141014$ times as great as that of ordinary solid matter. Suppose we represent the star as a uniform, solid, rigid sphere, both before and after the collapse. The star's initial radius was $9\mathrm{.}0105$ kmkm $($comparable to our sun$)$; its final radius is $18$ kmkm$.$