Secular Bar-Mode Evolution and Gravitational Waves From Neutron Stars

The secular instability and nonlinear evolution of the m=2 f-mode (bar-mode) driven by gravitational radiation reaction in a rapidly rotating, newly formed neutron star are reviewed. There are two types of rotating bars which generate quite different gravitational waveforms: those with large internal rotation relative to the bar figure (Dedekind-like bars) have GW frequency sweeping downward during the evolution, and those with small internal rotation (Jacobi-like) have GW frequency sweeping upward. Various sources of viscosity (which affects the instability) in hot nuclear matter are reexamined, and the possible effect of star-disk coupling on the bar-mode instability is also discussed.