R-modes in Accreting and Young Neutron Stars

Recent work has raised the exciting possibility that r-mode pulsations (Rossby waves) in rotating neutron star cores may be strong gravitational wave sources. Rapidly rotating young neutron stars born in supernovae enter the r-mode instability region within the first minutes of their lives and may spin down by substantial amounts due to gravitational radiation from r-modes. Accreting neutron stars in low-mass Xray binaries (LMXBs) are spun up by accretion to such short rotation periods that they may be unstable to r-mode pulsations as well. Gravitational waves from these neutron stars are strong enough to be detectable by second-generation, "enhanced" gravitational wave interferometers. I review the recent progress in understanding the r-mode instability in young and accreting neutron stars, with the focus on the issues of the coupling of the pulsations to the crust and nonlinear saturation amplitudes.