Characterizing Binary Black Hole Subpopulations in GWTC-4 with Binned Gaussian Processes: On the Origins of the 35 M ⊙ Peak
- 1Northwestern University
- 2NSF-Simons AI Institute for the Sky (SkAI)
Abstract
Understanding the astrophysical origins of binary black holes requires accurate and flexible modeling of multidimensional population properties. In this Letter, using a data-driven framework based on binned Gaussian processes, we characterize the joint distribution of BBH primary masses, mass ratios, and effective inspiral spins. We identify three distinct subpopulations in the GWTC-4 sample of observations and investigate their astrophysical origins. We find that only one of the three subpopulations exhibits the 35 M ⊙ peak, which is characterized by a strong preference for equal mass systems and isotropic spin orientations. Our inferred distributions are consistent with a predominantly dynamical origin of this feature. By comparing with theoretical simulations, we further show that the subpopulation that exhibits the 35 M ⊙ peak can exclusively comprise dynamically assembled systems in globular clusters, specifically if black hole birth spins are in the range (0.1−0.2), whereas the other two subpopulations require substantial contributions from alternative formation channels. We constrain the lower bound on the merger rate of BBHs in globular clusters to be 0.6 9 − 0.33 + 0.23 Gpc − 3 yr − 1 , which is consistent with most theoretical predictions (that can range from 0.2 to 57 Gpc −3 yr −1 depending on modeling assumptions). We conclude that dynamical formation in globular clusters remains a strong candidate for the origin of this excess near 30−40 M ⊙ and that more data and targeted parametric models are necessary to rigorously establish this interpretation.
Related
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BibTeX
@article{sridhar2026characterizing,
title = {{Characterizing Binary Black Hole Subpopulations in GWTC-4 with Binned Gaussian Processes: On the Origins of the 35 M ⊙ Peak}},
author = {Omkar Sridhar and Anarya Ray and Vicky Kalogera},
journal = {The Astrophysical Journal Letters},
year = {2026},
month = jul,
doi = {10.3847/2041-8213/ae8011},
url = {https://doi.org/10.3847/2041-8213/ae8011},
note = {CC BY},
}
RIS
TY - JOUR
TI - Characterizing Binary Black Hole Subpopulations in GWTC-4 with Binned Gaussian Processes: On the Origins of the 35 M ⊙ Peak
AU - Omkar Sridhar
AU - Anarya Ray
AU - Vicky Kalogera
PY - 2026
DA - 2026/07/03
JO - The Astrophysical Journal Letters
DO - 10.3847/2041-8213/ae8011
UR - https://doi.org/10.3847/2041-8213/ae8011
AB - Understanding the astrophysical origins of binary black holes requires accurate and flexible modeling of multidimensional population properties. In this Letter, using a data-driven framework based on binned Gaussian processes, we characterize the joint distribution of BBH primary masses, mass ratios, and effective inspiral spins. We identify three distinct subpopulations in the GWTC-4 sample of observations and investigate their astrophysical origins. We find that only one of the three subpopulations exhibits the 35 M ⊙ peak, which is characterized by a strong preference for equal mass systems and isotropic spin orientations. Our inferred distributions are consistent with a predominantly dynamical origin of this feature. By comparing with theoretical simulations, we further show that the subpopulation that exhibits the 35 M ⊙ peak can exclusively comprise dynamically assembled systems in globular clusters, specifically if black hole birth spins are in the range (0.1−0.2), whereas the other two subpopulations require substantial contributions from alternative formation channels. We constrain the lower bound on the merger rate of BBHs in globular clusters to be 0.6 9 − 0.33 + 0.23 Gpc − 3 yr − 1 , which is consistent with most theoretical predictions (that can range from 0.2 to 57 Gpc −3 yr −1 depending on modeling assumptions). We conclude that dynamical formation in globular clusters remains a strong candidate for the origin of this excess near 30−40 M ⊙ and that more data and targeted parametric models are necessary to rigorously establish this interpretation.
SN - 2041-8205
SN - 2041-8213
ER -