Four Eccentric Mergers Increase the Evidence that LIGO–Virgo–KAGRA’s Binary Black Holes Form Dynamically

Romero-Shaw, I. M.; Lasky, P. D.; Thrane, E.

doi:10.3847/1538-4357/ac9798

“…In summary, BBHs assembled in dense star clusters can explain the mass, effective spin, and rate of GW191109, unlike isolated binary evolution. Also note that our interpretation of GW191109 as having a dynamical origin is consistent with the findings in Romero-Shaw et al (2022). In this study, they used a reweighting method (Payne et al 2019;Romero-Shaw et al 2019) to calculate the eccentricity posterior probability distribution and found 72.19% of its posterior support at an eccentricity above 0.05 and 62.63% above 0.1.…”

Section: Dynamics In Dense Star Clusterssupporting

confidence: 85%

On the Likely Dynamical Origin of GW191109 and Binary Black Hole Mergers with Negative Effective Spin

Zhang,

Fragione,

Kimball

et al. 2023

ApJ

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With the growing number of binary black hole (BBH) mergers detected by LIGO/Virgo/KAGRA, several systems have become difficult to explain via isolated binary evolution, having components in the pair-instability mass gap, high orbital eccentricities, and/or spin–orbit misalignment. Here we focus on GW191109_010717, a BBH merger with component masses of 65 − 11 + 11 and 47 − 13 + 15 M ⊙ and an effective spin of − 0.29 − 0.31 + 0.42 , which could imply a spin–orbit misalignment of more than π/2 rad for at least one of its components. Besides its component masses being in the pair-instability mass gap, we show that isolated binary evolution is unlikely to reproduce the proposed spin–orbit misalignment of GW191109 with high confidence. On the other hand, we demonstrate that BBHs dynamically assembled in dense star clusters would naturally reproduce the spin–orbit misalignment and masses of GW191109 and the rates of GW191109-like events if at least one of the components were to be a second-generation BH. Finally, we generalize our results to all events with a measured negative effective spin, arguing that GW200225 also has a likely dynamical origin.

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“…However, we may still be overestimating the contribution from GCs, because multiple other formation channels and environments can produce BBH mergers with 𝜒 eff < 0. In the future, we can use more specific criteria to isolate the GC contribution to the merger rate, including, for example, the BBH population distribution of orbital eccentricity (Samsing 2018;Rodriguez et al 2018a;Zevin et al 2019;Arca Sedda et al 2021), which can be used to measure the fraction of BBHs assembled in GCs (Zevin et al 2021b;Romero-Shaw et al 2022), and the rate of hierarchical mergers (Rodriguez et al 2018b;Kimball et al 2021;Gerosa & Fishbach 2021) as inferred from the distribution of spin magnitudes (Fishbach et al 2017;Baibhav et al 2020;Fishbach et al 2022). Given robust predictions for the BBH population distribution of eccentricity, spin magnitudes, and/or masses as a function of GC properties, we may incorporate these additional BBH observables into our inference, and improve our constraints on GC properties.…”

Section: Discussionmentioning

confidence: 99%

Globular cluster formation histories, masses and radii inferred from gravitational waves

Fishbach¹,

Fragione²

2023

Preprint

0

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Globular clusters (GCs) are found in all types of galaxies and harbor some of the most extreme stellar systems, including black holes that may dynamically assemble into merging binaries (BBHs). Uncertain GC properties, including when they formed, their initial masses and sizes, affect their production rate of BBH mergers. Using the gravitational-wave catalog GWTC-3, we measure that dynamically-assembled BBHs -those that are consistent with isotropic spin directions -make up 61 +29 −44 % of the total merger rate, with a local merger rate of 10.9 +16.8 −9.3 Gpc −3 yr −1 rising to 58.9 +149.4 −46.0 Gpc −3 yr −1 at 𝑧 = 1. We assume this inferred rate describes the contribution from GCs and compare it against the Cluster Monte Carlo () simulation catalog to directly fit for the GC initial mass function, virial radius distribution, and formation history. We find that GC initial masses are consistent with a Schechter function with slope 𝛽 𝑚 = −1.9 +0.8 −0.8 . Assuming a mass function slope of 𝛽 𝑚 = −2 and a mass range between 10 4 -10 8 𝑀 , we infer a GC formation rate at 𝑧 = 2 of 5.0 +9.4 −4.0 Gpc −3 yr −1 , or 2.1 +3.9 −1.7 × 10 6 𝑀 Gpc −3 yr −1 in terms of mass density. We find that the GC formation rate probably rises more steeply than the global star formation rate between 𝑧 = 0 and 𝑧 = 3 (82% credibility) and implies a local number density that is 𝑓 ev = 22.6 +29.9 −16.2 times higher than the observed density of survived GCs. This is consistent with expectations for cluster evaporation, but may suggest that other environments contribute to the rate of BBH mergers with significantly tilted spins.

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“…Comparisons to the observed BH masses, spins, and merger rate indicate that a sizable fraction of the observed mergers may indeed originate in AGN disks (Tagawa et al 2021a;Gayathri et al 2021;Ford & McKernan 2022). The AGN channel could also explain some of the peculiar detections, such as those with a high mass (Tagawa et al 2021a;Gayathri et al 2023) and possibly high eccentricity (Tagawa et al 2021b;Gayathri et al 2022;Romero-Shaw et al 2022;Samsing et al 2022; but see Romero-Shaw et al 2020.…”

Section: Introductionmentioning

confidence: 93%

Shock Cooling and Breakout Emission for Optical Flares Associated with Gravitational-wave Events

Tagawa,

Kimura,

Haiman

et al. 2024

ApJ

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The astrophysical origin of stellar-mass black hole (BH) mergers discovered through gravitational waves (GWs) is widely debated. Mergers in the disks of active galactic nuclei (AGNs) represent promising environments for at least a fraction of these events, with possible observational clues in the GW data. An additional clue to unveil AGN merger environments is provided by possible electromagnetic emission from postmerger accreting BHs. Associated with BH mergers in AGN disks, emission from shocks emerging around jets launched by accreting merger remnants is expected. Here we compute the properties of the emission produced during breakout and the subsequent adiabatic expansion phase of the shocks, and we then apply this model to optical flares suggested to be possibly associated with GW events. We find that the majority of the reported flares can be explained by breakout and shock cooling emission. If the optical flares are produced by shock cooling emission, they would display moderate color evolution, possibly color variations among different events, and a positive correlation between delay time and flare duration and would be preceded by breakout emission in X-rays. If the breakout emission dominates the observed lightcurve, we predict the color to be distributed in a narrow range in the optical band and the delay time from GW to electromagnetic emission to be longer than ∼2 days. Hence, further explorations of delay time distributions, flare color evolution, and associated X-ray emission will be useful to test the proposed emission model for the observed flares.

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Four Eccentric Mergers Increase the Evidence that LIGO–Virgo–KAGRA’s Binary Black Holes Form Dynamically

Cited by 39 publications

References 140 publications

On the Likely Dynamical Origin of GW191109 and Binary Black Hole Mergers with Negative Effective Spin

On the Likely Dynamical Origin of GW191109 and Binary Black Hole Mergers with Negative Effective Spin

Globular cluster formation histories, masses and radii inferred from gravitational waves

Shock Cooling and Breakout Emission for Optical Flares Associated with Gravitational-wave Events

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