Andrea Passamonti, Kostas Glampedakis
Non-axisymmetric oscillations in rapidly rotating neutron stars can be driven unstable by gravitational-wave radiation via the CFS instability [see A. Passamonti et al. (2013)]. The fundamental mode (f-mode) is one of the main candidates which can suffer this instability and emit a copious amount of gravitational waves.
Among the various processes which can limit the growth of the f-mode is the non-linear bulk viscosity. The non-linear terms can be activated during the instability when the mode reaches a significant amplitude.
Our results show that non-linear bulk viscosity has a moderate impact on the size of the f-mode instability window, becoming an important factor and saturating the mode’s growth at a relatively large oscillation amplitude. In addition, we show that the action of bulk viscosity can be significantly mitigated by the presence of superfluidity in neutron star matter. We show similarly that non-linear bulk viscosity leads to a rather high saturation amplitude even for the r-mode instability.
Considering an f-mode-unstable neutron star located in the Virgo cluster and assuming a mode amplitude at the level allowed by bulk viscosity, we find that the emitted gravitational wave signal could be detectable by advanced ground-based detectors such as Advanced LIGO/Virgo and the Einstein telescope.
Reference / Figure
MNRAS, 422, 3327 (2012) arXiv:1112.3931v1 [astro-ph.SR]