{"schema":"pubphys.bundle/1","record":{"author":{"account_ref":null,"orcid":null},"builds_on":[],"content_schema":"pubphys.content.revision/1","content_sha256":"bf4e477ecb1716f1b3b8a9f8c208e66068ae6dd9626185545aa1fdd1b07e4a28","created":"2026-10-03T07:17:55Z","files":[],"origin":{"assisted_by":[],"kind":"seed"},"parents":["5475cf5dc5b1a72283d26dc95dc6e00d7ea4e00096a7c6492e409a1816eeb011"],"salt":"4fc6a928a06e12ad3824280b6335d26ea346c6e7bf1ae5729e315fa50aef4c46","schema":"pubphys.record/2","site":"pubphys.com","target":null,"type":"revision"},"content":{"answer_type":"mechanism","assisted_by":[],"external_id":"astro.star-formation-imf.low-efficiency","kind":"phenomenon","literature_status":"open","n":"1","parents":[],"plain":"If gas clouds simply collapsed under their own weight, galaxies would form stars about a hundred times faster than they do. Turbulence, magnetic fields and the push of newborn stars all slow it down, but which one sets the value is unknown.","posed_since":"1974","precise":"Molecular clouds convert gas into stars at efficiency per free-fall time eps_ff = SFR t_ff / M_gas ~ 0.01, with integrated cloud efficiencies of $\\sim 1-10\\,\\mathrm{percent}$ before dispersal. Explain the value and its scatter as a function of cloud surface density and virial parameter, separating the roles of supersonic turbulence, magnetic support and stellar feedback (photoionization, winds, radiation pressure, jets, supernovae).","problem_ref":null,"references":"","settled_by":"Simulations with all feedback channels that reproduce the measured eps_ff distribution across cloud populations, plus observations that measure eps_ff and its dependence on surface density in many galaxies.","status_note":"","title":"Why does gas form stars at only one percent per free-fall 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