We discuss the effect of nonlinear bulk viscosity and the associated reheating on the evolution of newly born , rapidly rotating neutron stars with r-modes destabilized through the Chandrasekhar-Friedman-Schutz ( CFS ) mechanism .
Bulk viscosity in these stars is due to the adjustment of the relative abundances of different particle species as the density of a fluid element is perturbed .
It becomes nonlinear when the chemical potential difference \delta \mu , measuring the chemical imbalance in the fluid element , becomes larger than the temperature T , which is generally much smaller than the Fermi energy .
From this scale on , the bulk viscosity increases much faster with \delta \mu than predicted by the usual , linear approximation .
This provides a potential saturation mechanism for stellar oscillation modes at a small to moderate amplitude .
In addition , bulk viscosity dissipates energy , which can lead to neutrino emission , reheating of the star , or both .
This is the first study to explicitly consider these effects in the evolution of the r-mode instability .
For stars with little or no hyperon bulk viscosity , these effects are not strong enough to prevent the r-modes from growing to amplitudes \alpha \sim 1 
or higher , so other saturation mechanisms will probably set in earlier .
The reheating effect makes spin-down occur at a higher temperature than would otherwise be the case , in this way possibly avoiding complications associated with a solid crust or a core superfluid .
On the other hand , stars with a substantial hyperon bulk viscosity and a moderate magnetic field saturate their mode amplitude at a low value , which makes them gravitational radiators for hundreds of years , while they lose angular momentum through gravitational waves and magnetic braking .