The Merger of Nonspinning Black Hole–Neutron Star Binaries

Abstract

We first study the nonspinning BH–NS binary merger to focus on the effect of the NS EOS, apart from the effect of the BH spin. The previous works by three groups [1–3] have found that the NSs in BH–NS binaries with high mass ratio $Q \gtrsim 4$ are barely subject to tidal disruption if the companion BH is not spinning. At the merger, the BH swallows most of the NS matter at one moment and the remnant disk mass is quite small or nearly equal to zero. Namely, the NS behaves approximately as a point particle even at the ISCO. Gravitational waves emitted in such a case have a similar waveform to that from a BH–BH binary. Because the behavior of NSs with high-mass BH companions does not show remarkable dependence on the EOS, they are unsuitable for the purpose of this chapter, i.e., to investigate the effect of the EOS on gravitational waves and final outcomes. Thus, we focus only on low mass-ratio binaries with $Q=2$ and 3 in this chapter. Also, we choose relatively low-mass NSs, because two-piece EOSs adopted in this thesis may not be appropriate for modeling a high-mass NS with high central density, due to the lack of model parameters in the high-density region.