Gravitational waves from low mass neutron stars

Abstract

Low mass neutron stars may be uniquely strong sources of gravitational waves. The neutron star crust can support large deformations for low mass stars. This is because of the star's weaker gravity. We find maximum ellipticities $ϵ$ (fractional difference in moments of inertia) that are 1000 times larger, and maximum quadrupole moments ${Q}_{22}$ over 100 times larger, for low mass stars than for $1.4{M}_{\ensuremath{\bigodot}}$ neutron stars. Indeed, we calculate that the crust can support an $ϵ$ as large as 0.005 for a minimum mass neutron star. A $0.12{M}_{\ensuremath{\bigodot}}$ star, that is maximally strained and rotating at 100 Hz, will produce a characteristic gravitational wave strain of ${h}_{0}=2.1\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}24}$ at a distance of 1 kpc. The gravitational wave detector Advanced LIGO should be sensitive to such objects through out the Milky Way Galaxy. A low mass neutron star could be uniquely identified from a large observed spin down rate and its discovery would have important implications for general relativity, supernova mechanisms, and possibly nucleosynthesis.