Excitation of the odd-parity quasi-normal modes of compact objects

TL;DR

This paper investigates how particles in unbounded orbits around neutron stars excite odd-parity quasi-normal modes, finding that such excitation is generally weak and higher multipole modes are also involved when excitation occurs.

Contribution

It provides the first detailed analysis of odd-parity $w$ mode excitation by particles in unbounded orbits around neutron stars, highlighting their weak excitation in realistic models.

Findings

Particles weakly excite $w$ modes in realistic neutron star models

Significant $w$ mode excitation also involves higher multipole modes

Excitation of $w$ modes is unlikely to be strong in astrophysical scenarios

Abstract

The gravitational radiation generated by a particle in a close unbounded orbit around a neutron star is computed as a means to study the importance of the $w$ modes of the neutron star. For simplicity, attention is restricted to odd parity (``axial'') modes which do not couple to the neutron star's fluid modes. We find that for realistic neutron star models, particles in unbounded orbits only weakly excite the $w$ modes; we conjecture that this is also the case for astrophysically interesting sources of neutron star perturbations. We also find that for cases in which there is significant excitation of quadrupole $w$ modes, there is comparable excitation of higher multipole modes.