March 2011

Erich Gaertig, Kostas D. Kokkotas

When a fast rotating neutron star becomes unstable to the CFS-mechanism, the non-axisymmetric instabilities will be a strong emitter of gravitational waves. The detection of these gravitational waves from oscillating neutron stars will allow the study of their interior, in the same way as helioseismology provides information about the interior of the Sun. It is expected that the identification of specific pulsation frequencies in the observational data will reveal the true properties of matter at densities that cannot be probed today by any other experiment.

This is the original suggestion about gravitational wave asteroseismology which was first applied to nonrotating neutron stars. The idea is to compute frequencies and damping times for different neutron star models and a huge variety of equations of state. Based on this data pool, model-independent relationships between oscillation frequencies/damping times and stellar key parametes like mass and radius can be established which will unambiguously pinpoint these parameters once gravitational waves from neutron stars can be detected.

In this study, gravitational wave asteroseismology has been extended to handle rapidly rotating neutron stars as well. The inclusion of rotational effects leads to several complications. First, non-axisymmetric mode frequencies split once the star is spinning and second, depending on the actual model, certain configurations can become secularly unstable. Nevertheless, it was possible to derive again model-independent relationships which in this case also include the angular velocity as fitting parameter.