Stripping of a neutron star in a close binary system in a pair with a black hole

TL;DR

This paper explores a new scenario where a neutron star is slowly stripped by a black hole in a binary system, potentially leading to observable electromagnetic transients and affecting the expected signals from such mergers.

Contribution

It introduces the possibility of slow neutron-star stripping in neutron star-black hole binaries, expanding the understanding of their final evolutionary stages.

Findings

Slow neutron-star stripping is possible in 50-90% of coalescing pairs.

Stripping can lead to neutron star explosion and electromagnetic transients.

Kilonova emission in this scenario is detectable due to large ejected mass.

Abstract

We consider the final evolutionary stages of a neutron star-black hole pair. According to the current paradigm, such systems eventually coalesce, which in some cases is accompanied by neutron-star tidal disruption. Using analytical methods, we show that the scenario of slow (of the order of several seconds) neutron-star stripping by the black hole is also possible, depending on the system parameters (the initial masses and intrinsic angular momenta of the components, the equation of state for the neutron star). Reaching the lower mass limit (about one tenth of the solar mass), the neutron star explodes to produce a comparatively powerful electromagnetic transient. Our population calculations show that the stripping mechanism is possible in 50-90% of the cases among all coalescing neutron star-black hole pairs, depending on the model assumptions about the evolution of close binary systems (the common-envelope efficiency parameter, the supernova explosion mechanism) and the initial metallicity of the stellar population. Because of the large mass of the ejected material, the kilonova emission in this scenario has good prospects of detection.