We present a simple spin evolution model that predicts that rapidly rotating accreting neutron stars will mainly be confined to a narrow range of spin-frequencies ; P = 1.5 - 5 ms .
This is in agreement with current observations of both neutron stars in the Low-Mass X-ray Binaries and millisecond radio pulsars .
The main ingredients in the model are : i ) the instability of r-modes above a critical spin rate , ii ) thermal runaway due to heat released as viscous damping mechanisms counteract the r-mode growth , and iii ) a revised estimate of the strength of dissipation due to the presence of a viscous boundary layer at the base of the crust in an old and relatively cold neutron star .
We discuss the gravitational waves that are radiated during the brief r-mode driven spin-down phase .
We also briefly touch on how the new estimates affects the predicted initial spin periods of hot young neutron stars .