{"schema":"pubphys.bundle/1","record":{"author":{"account_ref":null,"orcid":null},"builds_on":[],"content_schema":"pubphys.content.revision/1","content_sha256":"f067f2231ec610eb05cdf3ec35ad800669284c80a73320701141fd6fa561829a","created":"2026-10-15T23:43:22Z","files":[],"origin":{"assisted_by":[],"kind":"seed"},"parents":["7f4faf8f53f7921d5e0e2cabbde43adaca95be1e1ce584244f3c810bd93afba5","ce59fb6cd812fc05906d0c60a71c75ea22bc686bcf38e7c3ef7010834d98ee7b"],"salt":"920d492cc411af416bd869f044f71e5b57d1bd2fbf29298ed924077b607839a0","schema":"pubphys.record/2","site":"pubphys.com","target":null,"type":"revision"},"content":{"answer_type":"value","assisted_by":[],"external_id":"fluid.cavitation.sbsl-peak-temperature","kind":"well-posed","literature_status":"contested","n":"2","parents":[],"plain":"A single bubble trapped in a sound field collapses once per cycle and emits a flash of light lasting less than a billionth of a second. Nobody has measured directly how hot and how dense its center becomes.","posed_since":"","precise":"For a stably driven argon or air bubble in water (ambient radius $R_0 \\sim 5 \\times 10^{-4}\\,\\mathrm{cm}$, drive frequency $\\sim 2.5 \\times 10^{4}\\,\\mathrm{Hz}$, acoustic pressure amplitude $P_a \\sim 1.2\\ \\text{to}\\ 1.5\\,\\mathrm{bar}$), determine the spatially resolved peak temperature $T_{\\max}$ and gas density at collapse. Spectral fits in water give $T$ of order $6 \\times 10^{3}\\ \\text{to}\\ 2 \\times 10^{4}\\,\\mathrm{K}$, spectroscopy in concentrated sulfuric acid shows plasma signatures, and some models predict converging shocks heating a small core above $10^{5}\\,\\mathrm{K}$. An answer is a measured $T_{\\max}(r)$ with error bars, or a simulation that matches spectra, absolute photon number and pulse width simultaneously without free parameters.","problem_ref":"7f4faf8f53f7921d5e0e2cabbde43adaca95be1e1ce584244f3c810bd93afba5","references":"","settled_by":"A model-independent temperature diagnostic of the collapse core (for example time-resolved line broadening or X-ray or neutron yield limits) consistent with a parameter-free bubble-dynamics simulation.","status_note":"Temperature estimates in water remain model-dependent and differ by factors of several; no direct measurement of the core temperature as of 2026 (not re-verified for 2024-2026).","title":"Peak temperature and density inside a collapsing sonoluminescent 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