{"schema":"pubphys.bundle/1","record":{"author":{"account_ref":null,"orcid":null},"builds_on":[],"content_schema":"pubphys.content.revision/1","content_sha256":"75cac0b771b1094bb55f1b4f151eafc5140335aa89683f01b4ad516222af6c7f","created":"2026-10-03T07:17:55Z","files":[],"origin":{"assisted_by":[],"kind":"seed"},"parents":["5475cf5dc5b1a72283d26dc95dc6e00d7ea4e00096a7c6492e409a1816eeb011"],"salt":"c608abbabdb96185043bb8e8866ec6e357671d4aad64f11df5d89d20e40fde5b","schema":"pubphys.record/2","site":"pubphys.com","target":null,"type":"revision"},"content":{"answer_type":"identification","assisted_by":[],"external_id":"astro.galactic-gamma-ray-anomalies.positron-origin","kind":"phenomenon","literature_status":"open","n":"1","parents":[],"plain":"About 5e43 positrons per second annihilate in the Milky Way, mostly in the central bulge, and no known source class explains both the rate and the bulge-heavy pattern.","posed_since":"","precise":"Explain the $511\\,\\mathrm{keV}$ line (annihilation rate $\\sim 5e43\\,\\mathrm{positrons}/\\mathrm{s}$, bulge-to-disk luminosity ratio $\\sim 1$) with positrons injected below a few MeV (required by in-flight annihilation limits). Candidates: beta-plus decay of $\\mathrm{Al}-26$, $\\mathrm{Ti}-44$ and $\\mathrm{Co}-56$ from supernovae and novae, microquasars and low-mass X-ray binaries, past activity of Sgr A*, MeV-mass dark matter. Answer: a source mixture reproducing rate, morphology and spectrum, including positron transport.","problem_ref":null,"references":"","settled_by":"High-resolution imaging and spectroscopy of the line, resolving point sources or a profile that singles out one class.","status_note":"The COSI MeV mission, planned for launch in 2027, will map the line with better angular and energy resolution.","title":"What produces the Galaxy's 511 keV positron annihilation 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