{
  "abstract": "The LIGO-Virgo-KAGRA (LVK) collaboration has detected two binary neutron star (BNS) mergers, GW170817 and GW190425. While no clear electromagnetic counterpart was discovered for GW190425, a coincident counterpart to GW170817 (GRB170817A, AT 2017gfo) was discovered in an early-type galaxy, NGC 4993. Using broad-band photometry and an integrated optical spectrum, we measure a mass-weighted age of $12.4^{+0.5}_{-0.7}$ Gyr (90% credible) for NGC 4993, which is an estimate of the delay time between star formation and merger for the GW170817 progenitor. BNS systems are expected to have a power-law delay-time distribution (DTD) with a minimum delay time, $t_{\\rm min}$, of ~10 Myr and index $α\\approx -1$. This canonical DTD, convolved with the cosmic star-formation history, predicts ~16 BNS mergers at delay times of ~100 Myr for every BNS merger at 10 Gyr; under it, the chance of detecting even one merger as old as GW170817 is ~1.8%. The long delay time of GW170817 therefore implies many \"missing\" shorter-delay mergers if the canonical DTD holds. A DTD with $t_{\\rm min} = 12.6$ Gyr and $α= -1$ is favored over the canonical DTD by a factor of 40-140, and over short gamma-ray burst and Galactic double-NS DTDs by factors of 80-280. These results are in tension with current population synthesis models, the Milky Way double NS population, and the SGRB population. Explaining the LVK population requires either a dramatically different separation distribution than commonly assumed, an additional channel with a long delay time and comparable rate to an isolated-binary formation scenario, or a large population of BNS mergers missed in the LVK analysis. This result has wide-ranging implications for binary-population synthesis, chemical enrichment models, connections between BNS mergers and SGRBs, and future gravitational wave observations.",
  "abstract_shown": true,
  "affiliations": [],
  "article_type": null,
  "arxiv": "2610.40782",
  "author_total": 1,
  "authors": [
    {
      "name": "Ryan J. Foley"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/089hnf4bdq6zp.bib",
  "cited_by": 0,
  "doi": "10.48550/arxiv.2610.40782",
  "fulltext_url": null,
  "id": "089hnf4bdq6zp",
  "issns": [],
  "landing_url": "https://arxiv.org/abs/2610.40782",
  "language": null,
  "licence": "CC-BY-NC-SA-4.0",
  "licence_label": "CC BY-NC-SA 4.0",
  "licence_source": "article",
  "licence_url": "http://creativecommons.org/licenses/by-nc-sa/4.0/",
  "metadata_licence": "CC0-1.0",
  "native_subjects": [
    [
      "arxiv",
      "astro-ph.HE"
    ]
  ],
  "openalex": null,
  "pdf_url": "https://arxiv.org/pdf/2610.40782",
  "pmcid": null,
  "pmid": null,
  "published": "2026-10-29",
  "publisher": null,
  "ris": "https://research.draconitic.com/paper/089hnf4bdq6zp.ris",
  "sources": [
    {
      "first_seen": "2026-11-02T12:21:15Z",
      "native_id": "2610.40782",
      "source": "arxiv",
      "url": "https://arxiv.org/abs/2610.40782"
    }
  ],
  "subjects": [
    {
      "field": "astronomy",
      "origin": "arxiv:astro-ph.HE",
      "subfield": "high-energy-astrophysics"
    }
  ],
  "title": "Missing Mergers: On the Unexpected Delay-Time Distribution of Binary Neutron Star Mergers",
  "title_text": "Missing Mergers: On the Unexpected Delay-Time Distribution of Binary Neutron Star Mergers",
  "type": "preprint",
  "updated_at": "2026-11-04T15:20:51Z",
  "url": "https://research.draconitic.com/paper/089hnf4bdq6zp",
  "venue": "arXiv",
  "versions": []
}