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This study analyzes gravitational wave data from binary black hole mergers detected by LIGO-Virgo-KAGRA and identifies three distinct subpopulations with different formation origins. The researchers find that binary black holes with mass peaks around 10 and 35 solar masses have distinct characteristics in terms of mass ratios, spin alignments, and redshift evolution. Their analysis suggests these subpopulations likely arise from isolated binary evolution (79%), dynamical formation in globular clusters (14.5%), and higher-generation black hole mergers (2.5%), with evidence that these relative fractions change over cosmic time.
Why it matters
Understanding the formation channels of binary black holes helps astronomers reconstruct the evolutionary history of massive stars and dense stellar environments throughout cosmic time. This knowledge constrains models of stellar evolution, core collapse physics, and the environments where black holes form and merge, which is fundamental to understanding gravitational wave sources.
Understand the Science
arXiv:2603.17987v2 Announce Type: replace
Abstract: There is increasing evidence for multiple binary black hole~(BBH) subpopulations in the cumulative gravitational wave catalog by the LIGO-Virgo-KAGRA Collaboration. The astrophysical interpretation of this complex underlying population is subject to theoretical uncertainties in treatments of binary stellar evolution, core collapse, and host environments. In this textit{Letter}, using parametrized mixture models, we show that the BBH detection sample comprises three astrophysical subpopulations that are likely dominated by specific formation channels. In particular, we show that the $10M_{odot}$ peak and the $35M_{odot}$ feature in the BBH mass spectrum correspond to distinct mass-ratio, spin alignment, spin precession, and redshift evolution properties. We show that mass-based transitions reported in the distribution of BBH parameters naturally emerge from our inferred distributions without explicit modeling. Our results are consistent with the current observed population arising from specific relative abundances of isolated binary evolution, dynamical formation in globular clusters, and higher-generation BBH mergers. Under this interpretation, we constrain the relative underlying fraction of these channels to be $79.0^{+11.5}_{-10.9}%$, $14.5^{+11.6}_{-8.0}%$, and, $2.5^{+5.5}_{-1.8}%$, respectively, and find these relative fractions to be evolving over cosmic time with more than $1sigma$ confidence. Our interpretation relies on simple theoretical predictions that are mostly robust against uncertainties in BBH formation, with more definite conclusions expected in the near future.
Source: On the Astrophysical Origin of Binary Black Hole Subpopulations: A Tale of Three Channels?