Hitomi measured Perseus's core at 164 +/- 10 km/s, kinetic pressure under ten percent of thermal, in an atmosphere visibly cavitated, cold-fronted, and sloshing; XRISM finds the same 120-to-170 km/s calm in Centaurus, Abell 2029, Hydra A, and even disturbed Ophiuchus. Simulations of assembly plus AGN feedback predict stronger motions, and the heating budget now must balance cooling through channels that leave almost no kinetic fingerprint.
The model's clusters are stirred by construction, assembled through mergers and heated by feedback whose transport runs on turbulence, so kinetic energy is the working fluid of the whole thermal story. Atmospheres this still contradict the assembly history and disarm the heating mechanism simultaneously.
SCT's cluster atmospheres are quiet for the same structural reason they are stable: the gas was thermalized at deposition and carries a relic entropy floor (P22, P25, P29, P30), so neither assembly turbulence (the construction never ran) nor strong feedback transport (the floor stabilizes cooling structurally) is required to be present. The 164 km/s Perseus core is the settled state of born-hot gas with gigayears of calm behind it, and the XRISM generalization, quiet as the rule across cores including disturbed ones, is the deposition timeline read cluster by cluster. The paired crisis resolves as a pair: the cooling-flow entry's thermodynamic floor does the stabilizing that ΛCDM assigns to kinetic feedback, which is precisely why the kinetic fingerprint is missing, and the AGN trim around a deposited equilibrium without carrying the building.
The same calm propagates outward through the low non-thermal pressure fractions at R500, one quiescence budget from core to virial radius, and the residual motions that do exist (sloshing spirals, modest dispersions) read as secondary modulations from ongoing minor traffic atop a settled base. The framework's directional bet on the instrument era: XRISM's velocity maps will keep returning dispersions near the bottom of simulation distributions, correlated with relic-entropy indicators rather than with AGN power.
This is the quiet-core member of the relic-thermodynamics family: entropy floors, stable cooling, low turbulence, born-hot protoclusters, one deposition, audited kinematically. There is no need to make heated atmospheres hide their own weather.
The instrument era decides: XRISM and Athena velocity mapping across an unbiased sample finding turbulent pressure fractions rising to the simulated 10-to-30 percent levels, with dispersions tracking AGN power and merger state as feedback transport requires, would restore the stirred picture and remove the settled-deposit reading. The paired registered kills apply: the entropy floor absent at z of 2, or feedback shown sufficient and quiet by a first-principles transport mechanism, retires the relic stabilization the calm depends on.