We develop a fully reproducible observable level framework to test horizon scale models with Event Horizon Telescope (EHT) ring diameter constraints for M87* and Sagittarius A* (Sgr A*). Rather than reanalyzing interferometric visibilities, we use EHT data products for the ring diameter Formula: see text and the calibrated gravitational angular scale Formula: see text Formula: see text and map them to a baseline general relativity shadow diameter prediction. We quantify any net mismatch between the observed ring diameter and the baseline shadow scale by an effective shift parameter Formula: see text – 1, which aggregates emission and propagation effects at the observable level without specifying a microscopic plasma model. Calibration uncertainty in Formula: see text is propagated by treating Formula: see text as a nuisance parameter constrained by EHT and marginalizing it in the likelihood, including a split normal representation for asymmetric errors. Using EHT constraints, we obtain Formula: see text = 0.064±0.135 and Formula: see text = 0.038±0.232, both consistent with Formula: see text = 0 within current uncertainties. We further provide joint constraints in a common difference parameterization enabling compact cross target consistency tests that can be straightforwardly updated as improved EHT constraints become available.
Bustanji et al. (Thu,) studied this question.