{"record":{"author":{"account_ref":null,"orcid":null},"builds_on":[],"content_schema":"pubphys.content.revision/1","content_sha256":"c97f732feabc1c91ab2026eb234156568691d740d1d19d85464a87929e4e717c","created":"2026-10-03T07:18:07Z","files":[],"origin":{"assisted_by":[],"kind":"seed"},"parents":["4cb0a6f8827ec2141657f4461447e521ff1f75abb99e27db618281eabe4128c9","5475cf5dc5b1a72283d26dc95dc6e00d7ea4e00096a7c6492e409a1816eeb011"],"salt":"584c7377637973646c1d3fabdc39cabae349f43c614dd58272d177acc981cb01","schema":"pubphys.record/2","site":"pubphys.com","target":null,"type":"revision"},"content":{"answer_type":"mechanism","assisted_by":[],"external_id":"nuc.neutron-star-matter.sound-speed-peak-origin","kind":"phenomenon","literature_status":"open","n":"1","parents":[{"note":"","parent_revision":"4cb0a6f8827ec2141657f4461447e521ff1f75abb99e27db618281eabe4128c9","relation":"special_case"}],"plain":"If sound in neutron-star matter first speeds up beyond the free-quark value and then slows down again, there must be a peak. Where the peak lies and what causes it, for example a gradual change from nucleons to quarks, is unknown.","posed_since":"","precise":"Given $c_s^{2}(n) > c^{2}/3$ somewhere below the central density of a maximum-mass star, determine the density $n_{\\mathrm{peak}}$ of the maximum of $c_s^{2}$ and its height, and the microscopic mechanism: quarkyonic matter (a phase with a quark Fermi sea surrounded by a shell of nucleons near the Fermi surface), a hadron-quark crossover, a first-order transition, or strongly repulsive hadronic interactions. Answer: $n_{\\mathrm{peak}}/n_0$ and the maximum $c_s^{2}$ with uncertainties, plus a mechanism consistent with chiral EFT at low density and perturbative QCD at high density.","problem_ref":null,"references":"","settled_by":"Equation-of-state inference using 2 percent radius measurements across 1.2 to 2.1 solar masses and post-merger gravitational-wave spectra, compared with model calculations of each mechanism.","status_note":"","title":"Location and origin of the sound-speed maximum in dense matter","topic_ref":"dc9703fcc2930752e3222472fa4f0774fcc6cb72d19c4033b77e3e2b58d0fcb3"},"attested":{"attestation":{"batch":null,"client_id":null,"id_token_sha256":null,"kind":"platform"},"record_hash":"a43cf86f442c5dcacaa3bd3b344b960d25bfcabb06e95317866e8521bda17e62","schema":"pubphys.attested/1"},"envelope":{"attested_hash":"fecfa23427e1db739785db389f626437b84a491defe40876824da3c9bb61554b","platform_signature":{"key_id":"c6afc19b31429869751f06879c75cd64ea92654423d15b44be775bf1310a60da","sig":"rxbF29TZ1dA2cwMP6QSkHRZgrGIIbGLLsc8-bcJQeqPuMQsn6bqcjDBt0lvnVobcMrNBvGvdU3QZllzgYy-JAg"},"schema":"pubphys.envelope/1"},"record_hash":"a43cf86f442c5dcacaa3bd3b344b960d25bfcabb06e95317866e8521bda17e62","leaf_index":1783}