Abstract
Black-hole–neutron-star mergers resulting in the disruption of the neutron star and the formation of an accretion disk and/or the ejection of unbound material are prime candidates for the joint detection of gravitational-wave and electromagnetic signals when the next generation of gravitational-wave detectors comes online. However, the disruption of the neutron star and the properties of the postmerger remnant are very sensitive to the parameters of the binary (mass ratio, black-hole spin, neutron star radius). In this paper, we study the impact of the radius of the neutron star and the alignment of the black-hole spin on black-hole–neutron-star mergers within the range of mass ratio currently deemed most likely for field binaries () and for black-hole spins large enough for the neutron star to disrupt (). We find that (i) In this regime, the merger is particularly sensitive to the radius of the neutron star, with remnant masses varying from to for changes of only 2 km in the NS radius; (ii) of unbound material can be ejected with kinetic energy , a significant increase compared to low mass ratio, low spin binaries. This ejecta could power detectable postmerger optical and radio afterglows. (iii) Only a small fraction of the Advanced LIGO events in this parameter range have gravitational-wave signals which could offer constraints on the equation of state of the neutron star (at best of the events for a single detector at design sensitivity). (iv) A misaligned black-hole spin works against disk formation, with less neutron-star material remaining outside of the black hole after merger, and a larger fraction of that material remaining in the tidal tail instead of the forming accretion disk. (v) Large kicks can be given to the final black hole as a result of a precessing black-hole–neutron-star merger, when the disruption of the neutron star occurs just outside or within the innermost stable spherical orbit.
9 More- Received 23 December 2012
DOI:https://doi.org/10.1103/PhysRevD.87.084006
© 2013 American Physical Society