Black-Hole Remnants from Black-Hole–Neutron-Star Mergers

Abstract

Observations of gravitational waves and their electromagnetic counterparts may soon uncover the existence of coalescing compact binary systems formed by a stellar-mass black hole and a neutron star. These mergers result in a remnant black hole, possibly surrounded by an accretion disk. The mass and spin of the remnant black hole depend on the properties of the coalescing binary. We construct a map from the binary components to the remnant black hole using a sample of numericalrelativity simulations of different mass ratios q, (anti-)aligned dimensionless spins of the black hole aBH, and several neutron star equations of state. Given the binary total mass, the mass and spin of the remnant black hole can therefore be determined from the three parameters (q, aBH, Λ), where Λ is the tidal deformability of the neutron star. Our models also incorporate the binary black hole and test-mass limit cases and we discuss a simple extension for generic black hole spins. We combine the remnant characterization with recent population synthesis simulations for various metallicities of the progenitor stars that generated the binary system. We predict that black-hole-neutron-star mergers produce a population of remnant black holes with masses distributed around 7M and 9M . For isotropic spin distributions, nonmassive accretion disks are favoured: no bright electromagnetic counterparts are expected in such mergers.Introduction.-Mergers of a stellar-mass black hole (BH) and a neutron star (NS), hereafter BHNS, are expected sources of gravitational waves (GWs) detectable by ground-based laser-interferometers and possibly accompanied by electromagnetic counterparts [1][2][3][4][5][6][7]. No GW observations of BHNS binaries have been made to date. The 90% confidence upper limit on their merger rate is 610 Gpc −3 yr −1 [8]. To prepare these observations quantitative general-relativistic theoretical models of the GW and merger outcome are required.

Aligned-spin neutron-star–black-hole waveform model based on the effective-one-body approach and numerical-relativity simulations

“…In building the model, we have used final mass and spin fits from Ref. [79], the Λ NS − C NS relations of Ref. [76], and fits for the disk mass from Ref.…”

“…To obtain the final mass and spin from the initial parameters of the binary, we use the fits performed by Ref. [79], which account for the ejected mass.…”

Kilohertz gravitational waves from binary neutron star remnants: Time-domain model and constraints on extreme matter

“…However, for the reasons above, the ξ parameter cannot properly describe quantities affected by significant tidal distruption. An extreme case is for the example the disk mass in black-hole-neutron star binaries [108,109]. As discussed in the main text a main limitation in the construction of accurate postmerger models is the quality of NR postmerger waveforms.…”

Modeling the gravitational wave signature of neutron star black hole coalescences

“…The remnant model F BBH is the model for the final mass and spin of a BBH coalescence described in [77], and the coefficients p kji for the final mass M f and final spin χ f can be found in the Supplemental Material for [76]. Once the final mass and spin are determined, we find the ringdown frequency f RD and quality factor Q via…”

“…[75]; incorporating it in the amplitude model would require recalibrating the NSBH amplitude model itself as a whole and we leave this for future work. The final mass, M f , and final spin, χ f , of the remnant BH after merger are calculated using NSBH-specific fits for the remnant properties parametrized by tidal deformability [76],…”