Binary black hole mergers from globular clusters: Masses, merger rates, and the impact of stellar evolution

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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Searching for eccentricity: signatures of dynamical formation in the first gravitational-wave transient catalogue of LIGO and Virgo

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stz2996 ◽

2019 ◽

Vol 490 (4) ◽

pp. 5210-5216 ◽

Cited By ~ 19

Author(s):

Isobel M Romero-Shaw ◽

Paul D Lasky ◽

Eric Thrane

Keyword(s):

Black Holes ◽

Black Hole ◽

Bayesian Inference ◽

Gravitational Wave ◽

Globular Clusters ◽

Reference Frequency ◽

Binary Black Holes ◽

Binary Black Hole ◽

Upper Limits ◽

Formation History

ABSTRACT Binary black holes are thought to form primarily via two channels: isolated evolution and dynamical formation. The component masses, spins, and eccentricity of a binary black hole system provide clues to its formation history. We focus on eccentricity, which can be a signature of dynamical formation. Employing the spin-aligned eccentric waveform model seobnre, we perform Bayesian inference to measure the eccentricity of binary black hole merger events in the first gravitational-wave transient catalogue of LIGO and Virgo. We find that all of these events are consistent with zero eccentricity. We set upper limits on eccentricity ranging from 0.02 to 0.05 with 90 per cent confidence at a reference frequency of $10\, {\rm Hz}$. These upper limits do not significantly constrain the fraction of LIGO–Virgo events formed dynamically in globular clusters, because only $\sim 5{{\ \rm per\ cent}}$ are expected to merge with measurable eccentricity. However, with the gravitational-wave transient catalogue set to expand dramatically over the coming months, it may soon be possible to significantly constrain the fraction of mergers taking place in globular clusters using eccentricity measurements.

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Eccentric binary black hole mergers in globular clusters hosting intermediate-mass black holes

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stz2024 ◽

2019 ◽

Vol 488 (3) ◽

pp. 4370-4377 ◽

Cited By ~ 14

Author(s):

Giacomo Fragione ◽

Omer Bromberg

Keyword(s):

Black Holes ◽

Black Hole ◽

Globular Clusters ◽

Dynamical Friction ◽

Intermediate Mass ◽

Triple Systems ◽

Binary Black Hole ◽

Binary Orbit ◽

Short Time ◽

Intermediate Mass Black Holes

Abstract Globular clusters (GCs) may harbour intermediate-mass black holes (IMBHs) at their centres. In these dynamically active environments, stellar-mass black holes (SBHs) sink to the centre soon after formation, due to dynamical friction and start interacting among themselves and with the central IMBH. Likely, some of the SBHs will form bound systems with the IMBH. A fraction of those will be triple systems composed of binary SBHs and the IMBH acting as a third distant perturber. If the SBH binary orbit is sufficiently inclined, it can develop Lidov–Kozai (LK) oscillations, which can drive the system to high eccentricities and eventually to a merger due to gravitational wave (GW) emission on short time-scales. In this work, we focus on the dynamics of the IMBH–SBH–SBH triples and illustrate that these systems can be possible sources of GWs. A distinctive signature of this scenario is that a considerable fraction of these mergers are highly eccentric when entering the LIGO band (10 Hz). Assuming that $\sim 20{{\ \rm per\ cent}}$ of GCs host IMBHs and a GC density in the range $n_{{\rm GC}}=0.32\!-\!2.31\, \mathrm{Mpc}^{-3}$, we have estimated a rate $\Gamma =0.06\!-\!0.46\, \mathrm{Gpc}^{-3}\, \mathrm{yr}^{-1}$ of these events. This suggests that dynamically driven binary SBH mergers in this scenario could contribute to the merger events observed by LIGO/VIRGO. Full N-body simulations of GCs harbouring IMBHs are highly desirable to give a more precise constrain on this scenario.

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The effect of the metallicity-specific star formation history on double compact object mergers

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stz2840 ◽

2019 ◽

Vol 490 (3) ◽

pp. 3740-3759 ◽

Cited By ~ 34

Author(s):

Coenraad J Neijssel ◽

Alejandro Vigna-Gómez ◽

Simon Stevenson ◽

Jim W Barrett ◽

Sebastian M Gaebel ◽

...

Keyword(s):

Mass Transfer ◽

Black Hole ◽

Star Formation ◽

Star Formation Rate ◽

Formation Rate ◽

Compact Object ◽

Star Formation History ◽

Binary Black Hole ◽

Binary Evolution ◽

The Impact

ABSTRACT We investigate the impact of uncertainty in the metallicity-specific star formation rate over cosmic time on predictions of the rates and masses of double compact object mergers observable through gravitational waves. We find that this uncertainty can change the predicted detectable merger rate by more than an order of magnitude, comparable to contributions from uncertain physical assumptions regarding binary evolution, such as mass transfer efficiency or supernova kicks. We statistically compare the results produced by the COMPAS population synthesis suite against a catalogue of gravitational-wave detections from the first two Advanced LIGO and Virgo observing runs. We find that the rate and chirp mass of observed binary black hole mergers can be well matched under our default evolutionary model with a star formation metallicity spread of 0.39 dex around a mean metallicity 〈Z〉 that scales with redshift z as 〈Z〉 = 0.035 × 10−0.23z, assuming a star formation rate of $0.01 \times (1+z)^{2.77} / (1+((1+z)/2.9)^{4.7}) \, \rm {M}_\odot$ Mpc−3 yr−1. Intriguingly, this default model predicts that 80 per cent of the approximately one binary black hole merger per day that will be detectable at design sensitivity will have formed through isolated binary evolution with only dynamically stable mass transfer, i.e. without experiencing a common-envelope event.

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