I can't find the right answer, Help Please

A star of radius 5.1 × 105 km rotates about
its axis with a period of 26 days. The star
undergoes a supernova explosion, whereby its
core collapses into a neutron star of radius
28 km.
Estimate the period of the neutron star
(assume the mass remains constant).
Answer in units of s

Question

I can't find the right answer, Help Please

A star of radius 5.1 × 105 km rotates about
its axis with a period of 26 days. The star
undergoes a supernova explosion, whereby its
core collapses into a neutron star of radius
28 km.
Estimate the period of the neutron star
(assume the mass remains constant).
Answer in units of s

anonymous · Answer

You can use 'conservation of angular momentum' .

anonymous · Answer

but does that involve having a velocity?

anonymous · Answer

yes it does, but when you use period then it will disappear.  Actually, when you make equal inital and final angular momentum then youwill find that the period is inversely proportional  square of the radius of the star.