Constraining the Fraction of Binary Black Holes Formed in Isolation and Young Star Clusters with Gravitational-wave Data

Abstract

Ten binary black-hole mergers have already been detected during the first two observing runs of advanced LIGO and Virgo, and many more are expected to be observed in the near future. This opens the possibility for gravitational-wave astronomy to better constrain the properties of black hole binaries, not only as single sources, but as a whole astrophysical population. In this paper, we address the problem of using gravitational-wave measurements to estimate the proportion of merging black holes produced either via isolated binaries or binaries evolving in young star clusters. To this end, we use a Bayesian hierarchical modeling approach applied to catalogs of merging binary black holes generated using state-of-the-art population synthesis and N-body codes. In particular, we show that, although current advanced LIGO/Virgo observations only mildly constrain the mixing fraction f ∈ [0, 1] between the two formation channels, we expect to narrow down the fractional errors on f to 10 − 20% after a few hundreds of detections.

Properties and Astrophysical Implications of the 150 M⊙ Binary Black Hole Merger GW190521

“…If a star grows an oversized hydrogen envelope with respect to its helium core, it might directly collapse to a BH with mass ∼60-100 M e without entering the PI/PPI regime (Bouffanais et al 2019;Di Carlo et al 2019;Spera et al 2019). This scenario assumes that most of the hydrogen envelope collapses to a BH (see Sukhbold et al 2016 for a discussion of the uncertainties).…”

Fingerprints of Binary Black Hole Formation Channels Encoded in the Mass and Spin of Merger Remnants

“…Our knowledge of the merger rate from young star clusters is more uncertain, because massive stars form preferentially in young star clusters (Portegies Zwart et al 2010). Hence, young star clusters can provide a large fraction of the BBH mergers that occur in the field (see, e.g., Bouffanais et al 2019;di Carlo et al 2019a).…”

“…For instance, chirp masses can be used to constrain the global BH natal kick distribution (Zevin et al 2017; Barrett et al 2018), while their spin distribution can carry information on BH natal spins and BBH spin alignment in isolated (Gerosa et al 2018) and dynamical environments (Morawski et al 2018). As LIGO and Virgo reach full sensitivity and the number of detections increases, it will be possible to determine the most likely BH spin amplitude and the BBH spin orientation (Farr et al 2017;Stevenson et al 2017;Talbot & Thrane 2017;Arca Sedda & Benacquista 2019;Bouffanais et al 2019;Bavera et al 2020). Dissecting the formation history of BBHs from GW observations is a multifaceted problem that requires simultaneous accounting for single and binary stellar evolution, stellar dynamics, general relativity, and cosmology.…”

Endpoint of the up-down instability in precessing binary black holes

“…Accurate modeling of spin precession is crucial to interpret current and future GW events [10][11][12][13] Spins are clean astrophysical observables. For stellarmass BHs observed by LIGO/Virgo, they are a powerful tools to discriminate between isolated and dynamically assembled binaries [14][15][16][17][18]. BH spins encode information on some essential physics of massive stars including, but not limited to, core-envelope interactions, tides, mass transfer, supernova kicks, magnetic torquing, and internal gravity waves [19][20][21][22][23][24][25][26][27][28][29].…”