Fastest pulsar, yet. End of the r-mode?
At 716 Hz rotation frequrncy. Discovered in globular cluster Terzan 5
Previous rotation rate record was 642Hz, and it is thought, based on the sampling efficiency of searches down to ~ 1 kHz that there is a physical limit on rotation rate - something starts damping pulsar spin as it goes too high.
One of the more interesting damping mechanisms was r-mode damping through gravitational radiation emission (see here for explanation of r-modes (Rossby modes)
These models, curiously, predicted maximum rotation rates of < 700 Hz, and are formally wrong, now.
I'm sure they can be tweaked to let the maximum rate be a bit higher than predicted, but it is still an interesting constraint, and a slightly disappointing one as it reduces the prospects for detection of monochromatic gravitational radiation from nearby rapidly rotating neutron stars in dynamic equilibrium between spin-up torque from accretion and saturated r-mode breaking.