  We have discovered a 716-Hz eclipsing binary radio pulsar in the globular
cluster Terzan 5 using the Green Bank Telescope. It is the fastest-spinning
neutron star ever found, breaking the 23-year-old record held by the 642-Hz
pulsar B1937+21. The difficulty in detecting this pulsar, due to its very low
flux density and high eclipse fraction (~40% of the orbit), suggests that even
faster-spinning neutron stars exist. If the pulsar has a mass less than 2 Msun,
then its radius is constrained by the spin rate to be < 16 km. The short period
of this pulsar also constrains models that suggest gravitational radiation,
through an r-mode instability, limits the maximum spin frequency of neutron
stars.
