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

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##### Citation

Zappa, F., Bernuzzi, S., Pannarale, F., Mapelli, M., & Giacobbo, N. (2019). Black-Hole
Remnants from Black-Hole–Neutron-Star Mergers.* Physical Review Letters,* *123*:
041102. doi:10.1103/PhysRevLett.123.041102.

Cite as: https://hdl.handle.net/21.11116/0000-0003-680D-B

##### 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 numerical-relativity simulations of different mass ratios $q$,

(anti-)aligned dimensionless spins of the black hole $a_{\rm BH}$, 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

$(q,a_{\rm BH},\Lambda)$, where $\Lambda$ 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-eutrontar mergers produce a

population of remnant black holes with masses distributed around $7M_\odot$ and

$9M_\odot$. For isotropic spin distributions, nonmassive accretion disks are

favoured: no bright electromagnetic counterparts are expected in such mergers.

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 numerical-relativity simulations of different mass ratios $q$,

(anti-)aligned dimensionless spins of the black hole $a_{\rm BH}$, 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

$(q,a_{\rm BH},\Lambda)$, where $\Lambda$ 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-eutrontar mergers produce a

population of remnant black holes with masses distributed around $7M_\odot$ and

$9M_\odot$. For isotropic spin distributions, nonmassive accretion disks are

favoured: no bright electromagnetic counterparts are expected in such mergers.