Things that might go bump in the night: Assessing structure in the binary black hole mass spectrum

Abstract

Several features in the mass spectrum of merging binary black holes (BBHs) have been identified using data from the Third Gravitational Wave Transient Catalog (GWTC-3). These features are of particular interest as they may encode the uncertain mechanism of BBH formation. We assess if the features are statistically significant or the result of Poisson noise due to the finite number of observed events. We simulate realistic catalogs of BBHs whose underlying distribution does not have the features of interest, apply the analysis previously performed on GWTC-3, and determine how often such features are spuriously found. We find that two of the features found in GWTC-3, the peaks at ∼ 10 M and ∼ 35 M , cannot be explained by Poisson noise alone: peaks as significant occur in < 0.33% of catalogs generated from a featureless population. These peaks are therefore likely to be of astrophysical origin. However, additional structure beyond a power law, such as the purported dip at ∼ 14 M , can be explained by Poisson noise. We also provide a publicly-available package, GWMockCat, that creates simulated catalogs of BBH events with realistic measurement uncertainty and selection effects according to user-specified underlying distributions and detector sensitivities.

Bimodal Black Hole Mass Distribution and Chirp Masses of Binary Black Hole Mergers

“…They are corroborated by measurements in O3b (The LIGO Scientific Collaboration et al 2023;Tiwari 2022) and have complementary features in the inferred BH-mass distribution at about 9, 16, 30, and 57 M e (The LIGO Scientific Collaboration et al 2023;Tiwari & Fairhurst 2021;Tiwari 2022;Edelman et al 2023). Given the current number of BBH merger detections, the peaks at 9 and 30 M e seem robust whereas the significance of features around ≈16 M e is less clear (Talbot & Thrane 2018;Sadiq et al 2022;Wong & Cranmer 2022;Edelman et al 2023;Farah et al 2023). BBH mergers are theoretically expected to form through isolated binary evolution and dynamically in dense stellar environments (Mapelli 2021;Kocsis 2022;Mandel & Broekgaarden 2022).…”

On the primordial binary black hole mergings in LIGO-Virgo-Kagra data

“…However, a single PBH population is expected to produce a smooth chirpmass distribution of coalescing binaries, which is apparently not the case. There are two statistically significant bumps in the observed GWTC-3 chirp mass distribution of binary BHs at M ∼ 10M and M ∼ 30M [34]. The low-mass bump can be fitted with a population of binary BHs formed from massive stellar evolution.…”

What You Don’t Know Can Hurt You: Use and Abuse of Astrophysical Models in Gravitational-wave Population Analyses

“…In such models, 1D posterior distributions (usually fully marginalized, e.g., p(m 1 |d)), are modeled as splines, Gaussian processes, or using autoregression (Mandel et al 2017;Vitale et al 2019;Tiwari 2021Tiwari , 2022Veske et al 2021;Edelman et al 2022;Edelman et al 2023;Golomb & Talbot 2022;Rinaldi & Del Pozzo 2022;Callister & Farr 2023). While these approaches are less likely to impose stringent features into the posteriors (though see, e.g., Farah et al 2023), the number of unknown parameters is typically larger than for heuristic models, and the model parameters are not usually associated to any specific astrophysical quantity. Furthermore, these methods are not well suited to disentangle subpopulations, and are instead better suited to measuring the overall distribution of parameters.…”