{"paper":{"title":"Compact HII Regions as Clocks of Massive-Star Formation: Evidence for Long Formation Timescales","license":"http://arxiv.org/licenses/nonexclusive-distrib/1.0/","headline":"Compact HII regions act as clocks showing massive stars form over Myr timescales that increase with final mass.","cross_cats":[],"primary_cat":"astro-ph.SR","authors_text":"Mark Gieles, Paolo Padoan","submitted_at":"2026-02-05T21:11:27Z","abstract_excerpt":"We revisit the luminosity function (LF) of compact HII regions in the context of the inertial--inflow model (IIM), in which massive stars assemble over extended, mass-dependent timescales. The comparison of the compact-HII-region LF with that of OB stars has been used to estimate the compact-HII-phase lifetime and is often cited as evidence for the classical ``lifetime problem'' of HII regions. We show that once stellar growth during the ionizing phase is included, the LF comparison instead constrains massive-star formation timescales, so the lifetime problem turns into evidence for prolonged "},"claims":{"count":4,"items":[{"kind":"strongest_claim","text":"The joint LF constraints imply a growth law in which the formation time is about 4 Myr for a 60 M⊙ star, with an approximately square-root dependence on mass, as predicted by the IIM.","source":"verdict.strongest_claim","status":"machine_extracted","claim_id":"C1","attestation":"unclaimed"},{"kind":"weakest_assumption","text":"That the compact-HII-region phase lifetime is set solely by the time the star spends above a given ionizing luminosity while still accreting, with no significant contribution from other effects such as dust absorption or dynamical disruption of the region.","source":"verdict.weakest_assumption","status":"machine_extracted","claim_id":"C2","attestation":"unclaimed"},{"kind":"one_line_summary","text":"Massive stars in the Milky Way form over Myr timescales that increase with final mass, inferred from joint LF fitting of compact HII regions and OB stars under the inertial-inflow model.","source":"verdict.one_line_summary","status":"machine_extracted","claim_id":"C3","attestation":"unclaimed"},{"kind":"headline","text":"Compact HII regions act as clocks showing massive stars form over Myr timescales that increase with final mass.","source":"verdict.pith_extraction.headline","status":"machine_extracted","claim_id":"C4","attestation":"unclaimed"}],"snapshot_sha256":"acd67570c6a7adb6f1cff568786f2220d844dfc90e662ba1132cf9d7d8860ce7"},"source":{"id":"2602.06196","kind":"arxiv","version":2},"verdict":{"id":"a3ad9226-4002-4786-af54-2645478f9691","model_set":{"reader":"grok-4.3"},"created_at":"2026-05-16T06:28:25.651901Z","strongest_claim":"The joint LF constraints imply a growth law in which the formation time is about 4 Myr for a 60 M⊙ star, with an approximately square-root dependence on mass, as predicted by the IIM.","one_line_summary":"Massive stars in the Milky Way form over Myr timescales that increase with final mass, inferred from joint LF fitting of compact HII regions and OB stars under the inertial-inflow model.","pipeline_version":"pith-pipeline@v0.9.0","weakest_assumption":"That the compact-HII-region phase lifetime is set solely by the time the star spends above a given ionizing luminosity while still accreting, with no significant contribution from other effects such as dust absorption or dynamical disruption of the region.","pith_extraction_headline":"Compact HII regions act as clocks showing massive stars form over Myr timescales that increase with final mass."},"references":{"count":45,"sample":[{"doi":"10.1051/0004-6361/202243813","year":2023,"title":"2023, A&A, 674, A27, doi: 10.1051/0004-6361/202243813","work_id":"0e6a4829-15f9-4a54-a88d-4df76fa0a0ae","ref_index":1,"cited_arxiv_id":"","is_internal_anchor":false},{"doi":"10.1046/j.1365-8711.2001.04270.x","year":2001,"title":"2001, MNRAS, 322, 231, doi: 10.1046/j.1365-8711.2001.04022.x","work_id":"8bb90ab1-6c70-43ec-a616-cee37e93934d","ref_index":2,"cited_arxiv_id":"","is_internal_anchor":false},{"doi":"10.1046/j.1365-8711.2001.04311.x","year":2001,"title":"2001, MNRAS, 322, 231, doi: 10.1046/j.1365-8711.2001.04022.x","work_id":"8bb90ab1-6c70-43ec-a616-cee37e93934d","ref_index":3,"cited_arxiv_id":"","is_internal_anchor":false},{"doi":"10.1051/0004-6361/202346159","year":2023,"title":"J., Saxena, A., Cameron, A","work_id":"58fa2ee5-d21b-4270-8572-6e11e6cfc3ea","ref_index":4,"cited_arxiv_id":"","is_internal_anchor":false},{"doi":"10.3847/1538-4357/ad5f88","year":2024,"title":"doi:10.3847/1538-4357/ad5f88","work_id":"29378727-3e9b-42f1-9781-6fc126bd0c51","ref_index":5,"cited_arxiv_id":"","is_internal_anchor":false}],"resolved_work":45,"snapshot_sha256":"fd5ab8f2d4c8b5e97de610f971adeb5f0ec4dacf89985e0b1cf711326bd92a93","internal_anchors":2},"formal_canon":{"evidence_count":0,"snapshot_sha256":"258153158e38e3291e3d48162225fcdb2d5a3ed65a07baac614ab91432fd4f57"},"author_claims":{"count":0,"strong_count":0,"snapshot_sha256":"258153158e38e3291e3d48162225fcdb2d5a3ed65a07baac614ab91432fd4f57"},"builder_version":"pith-number-builder-2026-05-17-v1"}