Gravitational waves radiated by the coalescence of compact-object binaries containing a neutron star and a black hole are one of the most interesting sources for the ground-based gravitational-wave observatories Advanced LIGO and Advanced Virgo .
Advanced LIGO will be sensitive to the inspiral of a 1.4 M _ { \odot } neutron star into a 10 M _ { \odot } black hole to a maximum distance of \sim 900 Mpc .
Achieving this sensitivity and extracting the physics imprinted in observed signals requires accurate modeling of the binary to construct template waveforms .
In a neutron star–black hole binary , the black hole may have significant angular momentum ( spin ) , which affects the phase evolution of the emitted gravitational waves .
We investigate the ability of currently available post-Newtonian templates to model the gravitational waves emitted during the inspiral phase of neutron star–black hole binaries .
We restrict to the case where the spin of the black hole is aligned with the orbital angular momentum and compare several post-Newtonian approximants .
We examine restricted amplitude post-Newtonian waveforms that are accurate to third-and-a-half post-Newtonian order in the orbital dynamics and complete to second-and-a-half post-Newtonian order in the spin dynamics .
We also consider post-Newtonian waveforms that include the recently derived third-and-a-half post-Newtonian order spin-orbit correction and the third post-Newtonian order spin-orbit tail correction .
We compare these post-Newtonian approximants to the effective-one-body waveforms for spin-aligned binaries .
For all of these waveform families , we find that there is a large disagreement between different waveform approximants starting at low to moderate black hole spins , particularly for binaries where the spin is anti-aligned with the orbital angular momentum .
The match between the TaylorT4 and TaylorF2 approximants is \sim 0.8 for a binary with m _ { BH } / m _ { NS } \sim 4 and \chi _ { BH } = cJ _ { BH } / Gm ^ { 2 } _ { BH } \sim 0.4 .
We show that the divergence between the gravitational waveforms begins in the early inspiral at v \sim 0.2 for \chi _ { BH } \sim 0.4 .
Post-Newtonian spin corrections beyond those currently known will be required for optimal detection searches and to measure the parameters of neutron star–black hole binaries .
The strong dependence of the gravitational-wave signal on the spin dynamics will make it possible to extract significant astrophysical information from detected systems with Advanced LIGO and Advanced Virgo .