Effect of distant encounters on black hole binaries in globular clusters: Systematic increase of in-cluster mergers in the LISA band

Abstract The growing number of black hole binary (BHB) mergers detected by the Laser Interferometer Gravitational-Wave Observatory have the potential to enable an unprecedented characterisation of the physical processes and astrophysical conditions that govern the formation of compact binaries. In this paper, we focus on investigating the dynamical formation of BHBs in dense star clusters through a state-of-the-art set of 58 direct N-body simulations with N $\leqslant200\,000$ particles which include stellar evolution, gravitational braking, orbital decay through gravitational radiation, and galactic tidal interactions. The simulations encompass a range of initial conditions representing typical young globular clusters, including the presence of primordial binaries. The systems are simulated for $\sim 12$ Gyr. The dataset yields 117 BHB gravitational wave (GW) events, with 97 binaries merging within their host cluster and 20 merging after having been ejected. Only 8% of all ejected BHBs merge within the age of the Universe. Systems in this merging subset tend to have smaller separations and larger eccentricities, as this combination of parameters results in greater emission of gravitational radiation. We confirm known trends from Monte Carlo simulations, such as the anti-correlation between the mass of the binary and age of the cluster. In addition, we highlight for the first time a difference at low values of the mass ratio distribution between in-cluster and ejected mergers. However, the results depend on assumptions on the strength of GW recoils, thus in-cluster mergers cannot be ruled out at a significant level of confidence. A more substantial catalogue of BHB mergers and a more extensive library of N-body simulations are needed to constrain the origin of the observed events.

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Dynamical Formation and Evolution of Neutron Star and Black Hole Binaries in Globular Clusters

Physics of Relativistic Objects in Compact Binaries: From Birth to Coalescence - Astrophysics and Space Science Library ◽

10.1007/978-1-4020-9264-0_5 ◽

2009 ◽

pp. 199-243

Author(s):

Monica Colpi ◽

Bernadetta Devecchi

Keyword(s):

Black Hole ◽

Neutron Star ◽

Globular Clusters ◽

Black Hole Binaries ◽

Formation And Evolution

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mocca-survey Database I: Binary black hole mergers from globular clusters with intermediate mass black holes

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa2677 ◽

2020 ◽

Vol 498 (3) ◽

pp. 4287-4294

Author(s):

Jongsuk Hong ◽

Abbas Askar ◽

Mirek Giersz ◽

Arkadiusz Hypki ◽

Suk-Jin Yoon

Keyword(s):

Black Holes ◽

Black Hole ◽

Gravitational Waves ◽

Globular Clusters ◽

Stellar Mass ◽

Intermediate Mass ◽

Binary Black Holes ◽

Black Hole Binaries ◽

Binary Black Hole ◽

Intermediate Mass Black Holes

ABSTRACT The dynamical formation of black hole binaries in globular clusters that merge due to gravitational waves occurs more frequently in higher stellar density. Meanwhile, the probability to form intermediate mass black holes (IMBHs) also increases with the density. To explore the impact of the formation and growth of IMBHs on the population of stellar mass black hole binaries from globular clusters, we analyse the existing large survey of Monte Carlo globular cluster simulation data (mocca-survey Database I). We show that the number of binary black hole mergers agrees with the prediction based on clusters’ initial properties when the IMBH mass is not massive enough or the IMBH seed forms at a later time. However, binary black hole formation and subsequent merger events are significantly reduced compared to the prediction when the present-day IMBH mass is more massive than ${\sim}10^4\, \rm M_{\odot }$ or the present-day IMBH mass exceeds about 1 per cent of cluster’s initial total mass. By examining the maximum black hole mass in the system at the moment of black hole binary escaping, we find that ∼90 per cent of the merging binary black holes escape before the formation and growth of the IMBH. Furthermore, large fraction of stellar mass black holes are merged into the IMBH or escape as single black holes from globular clusters in cases of massive IMBHs, which can lead to the significant underpopulation of binary black holes merging with gravitational waves by a factor of 2 depending on the clusters’ initial distributions.

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Black hole binaries dynamically formed in globular clusters

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stx1015 ◽

2017 ◽

Vol 469 (4) ◽

pp. 4665-4674 ◽

Cited By ~ 63

Author(s):

Dawoo Park ◽

Chunglee Kim ◽

Hyung Mok Lee ◽

Yeong-Bok Bae ◽

Krzysztof Belczynski

Keyword(s):

Black Hole ◽

Globular Clusters ◽

Black Hole Binaries

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On the Eccentricity Distribution of Coalescing Black Hole Binaries Driven by the Kozai Mechanism in Globular Clusters

The Astrophysical Journal ◽

10.1086/378794 ◽

2003 ◽

Vol 598 (1) ◽

pp. 419-430 ◽

Cited By ~ 201

Author(s):

Linqing Wen

Keyword(s):

Black Hole ◽

Globular Clusters ◽

Black Hole Binaries

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A Dynamical Gravitational Wave Source in a Dense Cluster

Publications of the Astronomical Society of Australia ◽

10.1017/pasa.2016.30 ◽

2016 ◽

Vol 33 ◽

Cited By ~ 20

Author(s):

Jarrod R. Hurley ◽

Anna C. Sippel ◽

Christopher A. Tout ◽

Sverre J. Aarseth

Keyword(s):

Black Holes ◽

Black Hole ◽

Gravitational Wave ◽

Globular Clusters ◽

Binary Systems ◽

Star Cluster ◽

High Density ◽

Wave Source ◽

Black Hole Binaries ◽

Dense Cluster

AbstractMaking use of a new N-body model to describe the evolution of a moderate-size globular cluster, we investigate the characteristics of the population of black holes within such a cluster. This model reaches core-collapse and achieves a peak central density typical of the dense globular clusters of the Milky Way. Within this high-density environment, we see direct confirmation of the merging of two stellar remnant black holes in a dynamically formed binary, a gravitational wave source. We describe how the formation, evolution, and ultimate ejection/destruction of binary systems containing black holes impacts the evolution of the cluster core. Also, through comparison with previous models of lower density, we show that the period distribution of black hole binaries formed through dynamical interactions in this high-density model favours the production of gravitational wave sources. We confirm that the number of black holes remaining in a star cluster at late times and the characteristics of the binary black hole population depend on the nature of the star cluster, critically on the number density of stars and by extension the relaxation timescale.

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