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

Abstract

Making the most of the rapidly increasing population of gravitational-wave detections of black hole (BH) and neutron star (NS) mergers requires comparing observations with population synthesis predictions. In this work we investigate the combined impact from the key uncertainties in population synthesis modelling of the isolated binary evolution channel: the physical processes in massive binary-star evolution and the star formation history as a function of metallicity, 𝑍, and redshift 𝑧, S(𝑍, 𝑧). Considering these uncertainties we create 560 different publicly available model realizations and calculate the rate and distribution characteristics of detectable BHBH, BHNS, and NSNS mergers. We find that our stellar evolution and S(𝑍, 𝑧) variations can impact the predicted intrinsic and detectable merger rates by factors 10 2 -10 4 . We find that BHBH rates are dominantly impacted by S(𝑍, 𝑧) variations, NSNS rates by stellar evolution variations and BHNS rates by both. We then consider the combined impact from all uncertainties considered in this work on the detectable mass distribution shapes (chirp mass, individual masses and mass ratio). We find that the BHNS mass distributions are predominantly impacted by massive binary-star evolution changes. For BHBH and NSNS we find that both uncertainties are important. We also find that the shape of the delay time and birth metallicity distributions are typically dominated by the choice of S(𝑍, 𝑧) for BHBH, BHNS and NSNS. We identify several examples of robust features in the mass distributions predicted by all 560 models, such that we expect more than 95 percent of BHBH detections to contain a BH 8 M and have mass ratios 4. Our work demonstrates that it is essential to consider a wide range of allowed models to study double compact object merger rates and properties. Conversely, larger observed samples could allow us to decipher currently unconstrained stages of stellar and binary evolution.

Stable Mass Transfer Can Explain Massive Binary Black Hole Mergers with a High-spin Component

“…A number of formation channels have been put forward to explain the origin of BBH mergers (see Mandel & Broekgaarden 2022 for a review). In the isolated binary evolution channel, compact BH binaries are formed either through common-envelope evolution (e.g., Tutukov & Yungelson 1993;Lipunov et al 1997;Voss & Tauris 2003;Belczynski et al 2016;Eldridge & Stanway 2016;Stevenson et al 2017;Khokhlov et al 2018;Kruckow et al 2018;Spera et al 2019;Breivik et al 2020;Zevin et al 2020;Broekgaarden et al 2021) or through stable mass transfer between the BH and its companion (e.g., van den Heuvel et al 2017;Neijssel et al 2019;Bavera et al 2021;Gallegos-Garcia et al 2021;Shao & Li 2021). Alternatively, merging BHs can be formed via dynamical interactions in globular clusters (Downing et al 2010;Rodriguez et al 2016;Askar et al 2017;Perna et al 2019;Kremer et al 2020) or young stellar clusters (Ziosi et al 2014;Di Carlo et al 2019;Rastello et al 2020;Santoliquido et al 2020;Mapelli et al 2022).…”

Modelling the formation of the first two neutron star-black hole mergers, GW200105 and GW200115: metallicity, chirp masses and merger remnant spins

“…Two other models Pessimistic and Optimistic were also added to follow the effect of this change in parameters on our results. We acknowledge that while a portion of the partially constrained massive binary parameter space has been explored by our models, there still remains further uncertainties such as mass transfer efficiency, pre-supernova core mass to remnant mass models or different wind prescriptions (Broekgaarden et al 2021b). While exploring the entirety of this parameter space is beyond the scope of this study, more compact binary observations (having better signal-to-noise ratio that detects the masses and spins with better precision) will aid in restricting the uncertainties.…”

“…Future possible observations of more NS+BH mergers by LIGO (Belczynski et al 2016;Mapelli & Giacobbo 2018;Broekgaarden et al 2021c), NS+BH binaries by LISA (Chattopadhyay et al 2021;Wagg et al 2021) or even pulsars in binaries with BHs by radio telescopes like the SKA (Kyutoku et al 2019;Chattopadhyay et al 2021) will aid in shedding more light on the mass and spin distribution of these systems and hence put better constraints on massive binary evolution. Moreover, with more observations in gravitational waves as well as possible observations as radio pulsars of NS+BH systems, there will be higher scopes of differentiating the two NSBH and BHNS sub-populations.…”

Multi-messenger observations of binary neutron star mergers in the O4 run

“…Galactic NSNS (t coal < t H ) Power law model It is instructive to compare our mass probability distribution with others in the literature. To that purpose, we show in the right-hand panels of Figure 9 a comparison of the probability distributions of component masses implied by our result (red lines) with the corresponding distributions from a recently published population synthesis model (Broekgaarden et al 2021, their fiducial model) based on the COMPAS code (Riley et al 2022), and with the result of the study by Galaudage et al 2021, which models the Galactic NSNS population and the GW-detected NSNS binaries together. These comparisons show that, despite the large uncertainties and the simplifying assumptions, our results fall in a reasonably similar range as other results based on more refined methodologies.…”