The fastest spinning object ever measured is a millisecond pulsar, rotating at ~24% the speed of light.
A new study says that with SKA, we should find a handful more of these that could be spinning slightly faster. But there are unlikely any sub-millisecond pulsars.
There are numerous reasons / theories as to why there is an upper limit for pulsars spinning at higher frequencies, for example, the breakup velocity (they are very well held together!) and the spin-down induced by gravitational radiation.
This science tells us about matter under these extreme conditions!
https://arxiv.org/abs/2312.12185
#Pulsars #RadioAstronomy #Astrophysics #NuclearPhysics #Astrodon