Calculate New Period of Star After Shrinking Diameter

[joeypeter]

The mass of a star is 1.170×1031 kg and it performs one rotation in 28.30 day. Find its new period (in days) if the diameter suddenly shrinks to 0.610 times its present size. Assume a uniform mass distribution before and after.

How do I even start this problem? Can anyone give me step by step how to do this?

 

[tiny-tim]

Hi joeypeter!

We can give you one step:

Use conservation of angular momentum (what is it in this case?)