What is the fastest spinning rotation of a Neutron star?
As it turns out, the fastest spinning neutron star found yet is a pulsar 18000 light years away in the constelation of Sagittarius which scientist catalogued as PSR J1748-2446ad. Pulsars are neutron stars that rotate, are highly magnetic and emit a strong perpendicular beam of electromagnetic radiation.
This pulsar's speed is such that:
At its equator it is spinning at approximately 24% of the speed of light, or over 70,000 km per second.
PSR J1748-2446ad rotates a little over 700 times a second, and scientists have this to say on the theoretical limits of the rotation speed of a pulsar (from here):
Current theories of neutron star structure and evolution predict that pulsars would break apart if they spun at a rate of ~1500 rotations per second or more, and that at a rate of above about 1000 rotations per second they would lose energy by gravitational radiation faster than the accretion process would speed them up.
Fun experiment. Go here https://meettechniek.info/additional/additive-synthesis.html select Impuls, type the number 716 in the Sound Frequency field, and raise the volume. The sound you're hearing is the rotation frequency of the pulsar PSR J1748-2446ad.