{"schema":"pubphys.bundle/1","record":{"author":{"account_ref":null,"orcid":null},"builds_on":[],"content_schema":"pubphys.content.revision/1","content_sha256":"b314f0f618487e2b863fd9ac100ae79c00546d222b5688aa3d8bd3137b2c34a2","created":"2026-10-03T07:17:55Z","files":[],"origin":{"assisted_by":[],"kind":"seed"},"parents":["5475cf5dc5b1a72283d26dc95dc6e00d7ea4e00096a7c6492e409a1816eeb011"],"salt":"5c5f70d5ad4af791c63507ea281eee4e0430e457c7f01f481f6edb87710a52e2","schema":"pubphys.record/2","site":"pubphys.com","target":null,"type":"revision"},"content":{"answer_type":"mechanism","assisted_by":[],"external_id":"astro.sn-ia-progenitors.missing-companions","kind":"phenomenon","literature_status":"open","n":"1","parents":[],"plain":"If a white dwarf explodes while pulling gas from a normal star, that companion should survive and be seen near the center of the debris. Deep searches of young remnants have found no such star.","posed_since":"","precise":"Single-degenerate models predict a surviving donor at the center of young SN Ia remnants (for example Tycho, Kepler, SN 1006, SNR 0509-67.5), inflated and overluminous for $1e3 \\text{ to } 1e4\\,\\mathrm{yr}$ and moving at a few hundred km/s; deep HST searches exclude such stars in several remnants. Explain the nondetections (double-degenerate origin, spin-up/spin-down delay that lets the donor shrink, or misidentified models), and reconcile the observed hypervelocity white dwarfs moving above $1000\\,\\mathrm{km/s}$ with the number expected if double detonations eject surviving companions.","problem_ref":null,"references":"","settled_by":"A complete census of hypervelocity runaway white dwarfs from Gaia compared with the predicted ejection rate, together with deep companion limits in a larger set of Ia remnants.","status_note":"Hypervelocity runaway white dwarfs found in Gaia data since 2018 are candidate survivors of double detonations; whether their numbers match the SN Ia rate is debated.","title":"Why are surviving companion stars absent near Type Ia 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