{"schema":"pubphys.bundle/1","record":{"author":{"account_ref":null,"orcid":null},"builds_on":[],"content_schema":"pubphys.content.revision/1","content_sha256":"24acdd2a8d3b42702c1d7b2fa34ab6c16cc60dcb49b8517369085f3850e8e6d9","created":"2026-10-03T07:18:02Z","files":[],"origin":{"assisted_by":[],"kind":"seed"},"parents":["5475cf5dc5b1a72283d26dc95dc6e00d7ea4e00096a7c6492e409a1816eeb011"],"salt":"18e80b0b936f333878de21b0adda854445efe9dd1925d3a84e99fdbe2b9db9bb","schema":"pubphys.record/2","site":"pubphys.com","target":null,"type":"revision"},"content":{"answer_type":"value","assisted_by":[],"external_id":"cosmo.primordial-black-holes.merger-fraction","kind":"well-posed","literature_status":"open","n":"1","parents":[],"plain":"Gravitational-wave detectors have recorded hundreds of colliding black holes. Some of them might have been born in the early universe instead of from dying stars.","posed_since":"2016","precise":"Determine the fraction of the LIGO-Virgo-KAGRA binary black hole merger rate contributed by primordial black holes, or an upper bound on it, using mass, spin and redshift distributions. A sub-solar-mass black hole ($M < 1\\,M_{\\mathrm{sun}}$) in a merger would strongly favor primordial origin, since stellar collapse cannot make black holes below about $1\\,M_{\\mathrm{sun}}$ (the remaining alternative being neutron stars converted to black holes by captured dark matter); mergers at redshift $z > 30$ seen by third-generation detectors would also point to primordial origin.","problem_ref":null,"references":"","settled_by":"Detection or exclusion of sub-solar-mass compact binary mergers, plus redshift-resolved merger rates from Einstein Telescope or Cosmic Explorer.","status_note":"Mroz et al. (2024) bound compact halo objects of $1.8e-4 \\text{ to } 6.3\\,M_{\\mathrm{sun}}$ below 1 percent of dark matter; the O4 candidate S251112cm (2025), found by the sub-solar-mass search, has low significance (false-alarm rate about 1 per 6 yr), and no confident sub-solar-mass merger exists.","title":"Do any observed black-hole mergers involve primordial black 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