{"schema":"pubphys.bundle/1","record":{"author":{"account_ref":null,"orcid":null},"builds_on":[],"content_schema":"pubphys.content.revision/1","content_sha256":"d8acaf5a523e09e0ef19163d4e4f5b45c32c5784a8deb70b3f1a39b1852eaff9","created":"2026-10-03T07:17:55Z","files":[],"origin":{"assisted_by":[],"kind":"seed"},"parents":["5475cf5dc5b1a72283d26dc95dc6e00d7ea4e00096a7c6492e409a1816eeb011"],"salt":"936c446ceee236346683248b0efa4cf89cb7569bd4ef43d3a530958664b3ed34","schema":"pubphys.record/2","site":"pubphys.com","target":null,"type":"revision"},"content":{"answer_type":"identification","assisted_by":[],"external_id":"astro.ism-astrochemistry.bump-2175","kind":"well-posed","literature_status":"open","n":"1","parents":[],"plain":"Interstellar dust absorbs ultraviolet light most strongly near a wavelength of 2175 Angstrom. The bump's position barely changes from place to place while its width does, and no material reproduces both facts.","posed_since":"1965","precise":"Identify the carrier of the 2175 Angstrom extinction feature (candidates: graphitic carbon grains, PAH mixtures, hydrogenated carbon, carbon onions) and explain why its central wavelength is constant to about 1 percent across sightlines while its width varies by about 20 percent or more.","problem_ref":null,"references":"","settled_by":"Laboratory or ab initio optical spectra of a carrier population reproducing the fixed peak, variable width and observed strength per hydrogen atom.","status_note":"JWST detected the bump in a galaxy at $z \\sim 6.7$ (Witstok et al., Nature, 2023), requiring the carrier to form within about 1 Gyr.","title":"What carrier produces the 2175 Angstrom extinction 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