The Role of Core-collapse Physics in the Observability of Black Hole Neutron Star Mergers as Multimessenger Sources

Abstract

Recent 1D core-collapse simulations indicate a nonmonotonicity of the explodability of massive stars with respect to their precollapse core masses, which is in contrast to commonly used prescriptions. In this work, we explore the implications of these results on the formation of coalescing black hole (BH)–neutron star (NS) binaries. Furthermore, we investigate the effects of natal kicks and the NS’s radius on the synthesis of such systems and potential electromagnetic counterparts (EMCs) linked to them. Models based on 1D core-collapse simulations result in a BH–NS merger detection rate ( ∼ 2.3 yr−1), 5–10 times larger than the predictions of “standard” prescriptions. This is primarily due to the formation of low-mass BHs via direct collapse, and hence no natal kicks, favored by the 1D simulations. The fraction of observed systems that will produce an EMC, with the supernova engine from 1D simulations, ranges from 2% to 25%, depending on the NS equation of state. Notably, in most merging systems with EMCs, the NS is the first-born compact object, as long as the NS’s radius is ≲ 12 km. Furthermore, models with negligible kicks for low-mass BHs increase the detection rate of GW190426_152155-like events to ∼ 0.6 yr−1, with an associated probability of EMC ≤10% for all supernova engines. Finally, models based on 1D core-collapse simulations predict a ratio of BH–NSs to binary BHs’ merger rate density that is at least twice as high as other prescriptions, but at the same time overpredicting the measured local merger density rate of binary black holes.

A Channel to Form Fast-spinning Black Hole–Neutron Star Binary Mergers as Multimessenger Sources

“…The extension of our current grids with many other metallicities (especially lower metallicities) has been considered for our study in the near future. Román-Garza et al (2021) claimed that the fraction of NSfirst-born systems with different SN engines is 10% (see also Kinugawa et al 2022). Recent population synthesis studies Chattopadhyay et al 2021) showed that the fraction of NS-first-born NSBH binaries in total galactic NSBH binaries highly depends on the variations of binary population synthesis assumptions.…”

“…Since a fast-spinning BH can easily tidally disrupt the NS and produce bright EM signals (i.e., sGRBs and kilonovae), NSBH mergers formed via this formation channel can be potential multimessenger sources that allow us to discover their associated bright EM counterparts with a high probability after GW triggers (Zhu et al 2021c). Furthermore, as studied recently by Román-Garza et al (2021), core-collapse physics plays a critical role in the observability of the EM signals produced by NSBH mergers. In view of the lack of relevant research on the BH spin properties of this NS-firstborn formation channel for NSBH mergers, we investigate this formation channel of NSBHs with fast-spinning BHs in detail and study their corresponding tidal disruption probability.…”

Impact of Massive Binary Star and Cosmic Evolution on Gravitational Wave Observations II: Double Compact Object Rates and Properties

“…The behavior of the BHNS yield in most models, on the other hand, first modestly increases as a function of 𝑍 and then declines around Z (Figure 1; cf., Klencki et al 2018;Román-Garza et al 2021). This causes the yield to broadly peak in the range 0.2 Z Z Z , where the location of the peak varies between models as shown in Figure 1.…”

Population Properties of Gravitational-Wave Neutron Star--Black Hole Mergers

“…Alternatively, the first-born compact object in NSBH mergers could be a NS. Román-Garza et al (2021) recently claimed that the fraction of the systems with a first-born NS with different supernova engines is ∼ 10%. This scenario would lead to a group of NSBH mergers with a unique spin distribution, which has not been discovered by present GW detections.…”