{"record":{"author":{"account_ref":null,"orcid":null},"builds_on":[],"content_schema":"pubphys.content.revision/1","content_sha256":"d6a287ff4814768b776df24cc7d35b62d44c951e4342c58341b4b969e004c94d","created":"2026-10-03T07:17:55Z","files":[],"origin":{"assisted_by":[],"kind":"seed"},"parents":["5475cf5dc5b1a72283d26dc95dc6e00d7ea4e00096a7c6492e409a1816eeb011"],"salt":"6bec45ce22077aeecfbf4abc347658572aa057e0f1092bbad2d9e316e04d9a63","schema":"pubphys.record/2","site":"pubphys.com","target":null,"type":"revision"},"content":{"answer_type":"value","assisted_by":[],"external_id":"astro.sn-ia-progenitors.single-double-degenerate","kind":"well-posed","literature_status":"contested","n":"1","parents":[],"plain":"A white dwarf may explode after taking matter from an ordinary companion star, or after merging or interacting with a second white dwarf. Astronomers still do not know which route makes most of the observed explosions.","posed_since":"","precise":"For normal SNe Ia in Milky Way-like galaxies, determine the fraction $f_{\\mathrm{DD}}$ produced by double-degenerate systems (two white dwarfs) versus single-degenerate systems (white dwarf plus nondegenerate donor). The answer must be consistent with the delay-time distribution (approximately proportional to $t^{-1}$), the absence of stripped hydrogen in nebular spectra (no detection in 111 events, Tucker et al. 2020, with limits well below the $0.1\\ \\text{to}\\ 0.5\\,M_{\\mathrm{sun}}$ expected from a hydrogen-rich donor), early light-curve excesses and the measured rate per unit stellar mass.","problem_ref":null,"references":"","settled_by":"A population synthesis calibrated on the delay-time distribution combined with complete nebular-spectrum hydrogen limits and companion searches across a volume-limited SN Ia sample.","status_note":"Most evidence through 2025 favours double-degenerate systems for the majority, but single-degenerate contributions to subclasses remain under debate.","title":"What fraction of Type Ia supernovae come from two white dwarfs?","topic_ref":"725883c9f1fa87da8eacd23b3ad9211426658a588d96f1c1bbacc3e7a502c79e"},"attested":{"attestation":{"batch":null,"client_id":null,"id_token_sha256":null,"kind":"platform"},"record_hash":"9d628e0b69c1b3bb679ea69e9725a71df49639b6d3bd93bb5444bec597a7c21c","schema":"pubphys.attested/1"},"envelope":{"attested_hash":"b18b10bf78b53332f5af36ff70801a6e7c89531d56e53a4927a91704a903f25f","platform_signature":{"key_id":"c6afc19b31429869751f06879c75cd64ea92654423d15b44be775bf1310a60da","sig":"jgMoD03kFJmuTFEiGsOkHKrhUTzkmnrFzaWOmOgI8H40CiRPgy9k-6IUNehaEgU9-8kLtz_QQQGioik2G119CQ"},"schema":"pubphys.envelope/1"},"record_hash":"9d628e0b69c1b3bb679ea69e9725a71df49639b6d3bd93bb5444bec597a7c21c","leaf_index":611}