{
  "abstract": "We analyze the mass-ratio and effective-spin ( χ eff ) distributions of binary black hole mergers in the latest gravitational-wave catalog, GWTC-5, as a function of primary mass. Using hierarchical Bayesian inference with flexible Gaussian-process population models, we identify four distinct mass regions separated by transitions in both mass-ratio and spin properties. Below ∼18 M ⊙ the population strongly favors equal-mass binaries and exhibits a narrow, symmetric χ eff distribution peaked at positive values. The positive skewness previously reported for the overall population is absent from this low-mass component, and it is most likely associated with higher-mass binaries. In the range 18–30 M ⊙ , the mass-ratio distribution becomes substantially flatter, while the χ eff distribution broadens and shifts to a peak consistent with zero. The region associated with the feature near ≃35 M ⊙ returns to a narrow χ eff distribution consistent with symmetry at zero and strongly favors equal-mass binaries. Above ≃45 M ⊙ , both the mass-ratio and χ eff distributions broaden significantly. The inferred support of the spin distribution converges toward the range expected for binaries containing remnants of previous black hole mergers, making the highest-mass region fully consistent with a star cluster population of hierarchical mergers. The close correspondence between transitions in mass ratio and effective spin suggests that different primary-mass ranges trace distinct formation channels, with isolated binary or triple evolution likely dominating the lower-mass population and dynamical assembly becoming increasingly important at higher masses.",
  "abstract_shown": true,
  "affiliations": [
    "Cardiff University",
    "Williams College",
    "Northwestern University",
    "Max Planck Institute for Astrophysics"
  ],
  "article_type": null,
  "arxiv": null,
  "author_total": 7,
  "authors": [
    {
      "affs": [
        0
      ],
      "name": "Elizabeth Flanagan"
    },
    {
      "affs": [
        0
      ],
      "name": "Fabio Antonini",
      "orcid": "0000-0003-3138-6199"
    },
    {
      "affs": [
        1
      ],
      "name": "Thomas Callister"
    },
    {
      "affs": [
        2
      ],
      "name": "Debatri Chattopadhyay"
    },
    {
      "affs": [
        0
      ],
      "name": "Fani Dosopoulou"
    },
    {
      "affs": [
        0
      ],
      "name": "Isobel Romero-Shaw"
    },
    {
      "affs": [
        3
      ],
      "name": "Jakob Stegmann"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/0h8bhz49zrh19.bib",
  "cited_by": 0,
  "doi": "10.3847/2041-8213/aeb120",
  "fulltext_url": null,
  "id": "0h8bhz49zrh19",
  "issns": [
    "2041-8213",
    "2041-8205"
  ],
  "landing_url": "https://iopscience.iop.org/article/10.3847/2041-8213/aeb120",
  "language": null,
  "licence": "CC-BY-4.0",
  "licence_label": "CC BY 4.0",
  "licence_source": "article",
  "licence_url": "https://creativecommons.org/licenses/by/4.0/",
  "metadata_licence": null,
  "native_subjects": [
    [
      "feed-journal",
      "astronomy/general"
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  "pdf_url": "https://iopscience.iop.org/article/10.3847/2041-8213/aeb120/pdf",
  "pmcid": null,
  "pmid": null,
  "published": "2026-11-05",
  "publisher": "American Astronomical Society",
  "ris": "https://research.draconitic.com/paper/0h8bhz49zrh19.ris",
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    {
      "first_seen": "2026-11-05T12:20:12Z",
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  ],
  "subjects": [
    {
      "field": "astronomy",
      "origin": "journal-openalex:3103|Stellar, planetary, and galactic studies",
      "subfield": "stellar"
    }
  ],
  "title": "Transitions in the Mass-ratio and Spin Properties of Binary Black Holes in GWTC-5",
  "title_text": "Transitions in the Mass-ratio and Spin Properties of Binary Black Holes in GWTC-5",
  "type": "peer-reviewed",
  "updated_at": "2026-11-07T00:20:58Z",
  "url": "https://research.draconitic.com/paper/0h8bhz49zrh19",
  "venue": "The Astrophysical Journal Letters",
  "versions": []
}