{"schema":"pubphys.bundle/1","record":{"author":{"account_ref":null,"orcid":null},"builds_on":[],"content_schema":"pubphys.content.revision/1","content_sha256":"df34ac71d1e26627890eff470dd801022d8b5cc7596dc072c3a7283082249451","created":"2026-10-15T23:43:22Z","files":[],"origin":{"assisted_by":[],"kind":"seed"},"parents":["5c11047ad3e9a1cdbc536242c7229e1dc63e61211ea21ab5138f3b8586d20c31","ce59fb6cd812fc05906d0c60a71c75ea22bc686bcf38e7c3ef7010834d98ee7b"],"salt":"82cb5ef88e781765f0bb561354efd92ee4606a943f064325e95c16eaddb6c9ce","schema":"pubphys.record/2","site":"pubphys.com","target":null,"type":"revision"},"content":{"answer_type":"value","assisted_by":[],"external_id":"astro.neutron-star-interiors.cas-a-cooling","kind":"well-posed","literature_status":"contested","n":"2","parents":[],"plain":"The young neutron star in the Cassiopeia A remnant appeared to cool by a few percent in ten years, much faster than expected. This was explained as neutrons becoming superfluid, but the measurement depends on instrument calibration.","posed_since":"2010","precise":"Chandra spectra of the Cas A neutron star (age about $340\\ \\mathrm{yr}$) have been fit with a surface temperature decline of approximately 1 to 4 percent per decade, the value and significance depending on detector mode, calibration and interstellar absorption modeling. Determine $dT_{s}/dt$ with systematics, and decide whether it requires neutrino emission from Cooper-pair formation at the onset of neutron triplet superfluidity (critical temperature of order $5 \\times 10^{8}\\text{ to }10^{9}\\ \\mathrm{K}$) or permits slower standard cooling.","problem_ref":"5c11047ad3e9a1cdbc536242c7229e1dc63e61211ea21ab5138f3b8586d20c31","references":"","settled_by":"A cross-calibrated multi-instrument temperature history over about 25 yr with the absorption column fit jointly.","status_note":"An analysis of all Chandra ACIS-S data found a continued decline constraining superfluid gaps (Shternin et al., MNRAS, 2022), while 2026 papers propose alternative cooling routes such as Urca processes (Potekhin and Yakovlev, JHEAp, 2026).","title":"Is the Cassiopeia A neutron star cooling unusually 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