Water Maser Discs: Measured Keplerian Shear in NGC 4258 Against a Shear Ceiling

This study asks how the directly measured shear in a water megamaser disc compares with a derived shear ceiling. Using published ranges for the relevant source properties and standard relations stated in full, the computation converts the observed quantities into orbital shear rate in per second and compares each value with a spin-torsion density ceiling and the shear rate derived from it. The headline values are: v_inner_km_s = 1095, shear_inner_per_s = 3.801e-10, shear_ratio_inner = 9.414e-35, period_inner_yr = 785.8, rhoA_kg_m3 = 9.718e+57, shear_max_per_s = 4.037e+24. The comparison is a computation from stated assumptions and published inputs, not a measurement, and it is reported at face value: where the converted values fall far from the ceiling, that separation is the result, and where a standard relation is itself placed under strain by the data, that strain is identified separately from any question about the ceiling.