New insights on binary black hole formation channels after GWTC-2: young star clusters versus isolated binaries

Abstract

With the recent release of the second gravitational-wave transient catalogue (GWTC-2), which introduced dozens of new detections, we are at a turning point of gravitational wave astronomy, as we are now able to directly infer constraints on the astrophysical population of compact objects. Here, we tackle the burning issue of understanding the origin of binary black hole (BBH) mergers. To this effect, we make use of state-of-the-art population synthesis and N-body simulations, to represent two distinct formation channels: BBHs formed in the field (isolated channel) and in young star clusters (dynamical channel). We then use a Bayesian hierarchical approach to infer the distribution of the mixing fraction $f$, with $f=0$ ($f=1$) in the pure dynamical (isolated) channel. %that controls the proportion of isolated and dynamical BBHs. We explore the effects of additional hyper-parameters of the model, such as the spread in metallicity ${\sigma }_{\text{Z}}$ and the parameter ${\sigma }_{\text{sp}}$, describing the distribution of spin magnitudes. We find that the dynamical model is slightly favoured with a median value of $f=0.26$, when ${\sigma }_{\text{sp}}=0.1$ and ${\sigma }_{\text{Z}}=0.4$. Models with higher spin magnitudes tend to strongly favour dynamically formed BBHs ($f\le 0.1$ if ${\sigma }_{\text{sp}}=0.3$). Furthermore, we show that hyper-parameters controlling the rates of the model, such as ${\sigma }_{\mathrm{Z}}$, have a large impact on the inference of the mixing fraction, which rises from $0.18$ to $0.43$ when we increase ${\sigma }_{\text{Z}}$ from 0.2 to 0.6, for a fixed value of ${\sigma }_{\text{sp}}=0.1$. Finally, our current set of observations is better described by a combination of both formation channels, as a pure dynamical scenario is excluded at the $99\%$ credible interval, except when the spin magnitude is high.

13 pages, 10 figures, 2 tables, published in MNRAS

References in corpus (19)

• Binary interaction dominates the evolution of massive stars
• GW190814: Gravitational Waves from the Coalescence of a 23 M${}_{\odot }$ Black Hole with a 2.6 M${}_{\odot }$ Compact Object
• MOCCA-SURVEY Database I: Coalescing Binary Black Holes Originating From Globular Clusters
• Illuminating Black Hole Binary Formation Channels with Spins in Advanced LIGO
• One Channel to Rule Them All? Constraining the Origins of Binary Black Holes using Multiple Formation Pathways
• Merging black hole binaries: the effects of progenitor's metallicity, mass-loss rate and Eddington factor
• Lidov-Kozai Cycles with Gravitational Radiation: Merging Black Holes in Isolated Triple Systems
• The Dynamical Evolution of Stellar Black Holes in Globular Clusters
• Merging black holes in young star clusters
• Dynamics of stellar black holes in young star clusters with different metallicities - II. Black hole-black hole binaries
• A Highly Spinning and Aligned Binary Black Hole Merger in the Advanced LIGO First Observing Run
• The cosmic merger rate of stellar black hole binaries from the Illustris simulation
• Stellar-mass black holes in young massive and open stellar clusters and their role in gravitational-wave generation
• AGN Disks Harden the Mass Distribution of Stellar-mass Binary Black Hole Mergers
• Hierarchical black hole mergers in young, globular and nuclear star clusters: the effect of metallicity, spin and cluster properties
• The properties of merging black holes and neutron stars across cosmic time
• Repeated mergers and ejection of black holes within nuclear star clusters
• Effective spin distribution of black hole mergers in triples
• Flipping spins in mass transferring binaries and origin of spin-orbit misalignment in binary black holes

Cited by in corpus (9)

• Implications of Eccentric Observations on Binary Black Hole Formation Channels
• Binary Black Hole Formation with Detailed Modeling: Stable Mass Transfer Leads to Lower Merger Rates
• Dynamics of binary black holes in low-mass young star clusters
• Spin misalignment of black hole binaries from young star clusters: implications for the origin of gravitational waves events
• GW190521 formation via three-body encounters in young massive star clusters
• Gravitational waves from Population III binary black holes are consistent with LIGO/Virgo O3a data for the chirp mass larger than $\sim 20M_{\odot }$
• Gravitational waves from the remnants of the first stars in nuclear star clusters
• Binary black hole mergers from young massive and open clusters: comparison to GWTC-2 gravitational wave data
• Who Ordered That? Unequal-Mass Binary Black Hole Mergers Have Larger Effective Spins