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    "story_id": "mp-2026-09-05-014",
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    "position": 14,
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    "headline": "Gravitational Waves Became a Population, Not a Rarity",
    "slug": "gravitational-waves-became-a-population-not-a-rarity",
    "dek": "The newest O4 catalogues each add roughly one hundred detections, shifting inference toward subpopulations and cosmic history.",
    "summary": "The newest O4 catalogues each add roughly one hundred detections, shifting inference toward subpopulations and cosmic history.",
    "body_text": "A review of the fourth LIGO-Virgo-KAGRA observing run describes a field moving from exceptional single events to catalog-scale inference. Recent catalogues each contain about one hundred new detections, including unusually loud signals and sources unlike earlier examples. The larger samples support evidence for multiple compact-binary subpopulations and tighter work on stellar evolution, gravity and the Universe's expansion. The final O4 catalogue is due in December 2026, so this paper synthesizes published run results rather than announcing that final release.",
    "why_it_matters": "The newest O4 catalogues each add roughly one hundred detections, shifting inference toward subpopulations and cosmic history.",
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    "importance": 8,
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    "first_published_at": "2026-09-05T09:00:00.000-04:00",
    "modified_at": "2026-09-05T09:00:00.000-04:00",
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    "tags": [
      "gravitational waves",
      "LIGO",
      "compact binaries"
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    {
      "source_id": "source-2026-09-05-014",
      "title": "arXiv preprint 2609.03859",
      "publisher": "arXiv",
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      "published_at": "2026-09-03T09:50:08.000-04:00",
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    "title": "Gravitational Waves Became a Population, Not a Rarity",
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    "published_at": "2026-09-05T09:00:00.000-04:00",
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