The results of both of these experiments only hold if the GRMHD models used as synthetic data provide a good description of M87 . As multiple observation epochs become available , it will be possible to explicitly measure the statistics of the stochastic fluctuations , empirically addressing this assumption . It will also enable direct ensemble - to - ensemble comparison like that described in Kim et al . ( 2016 ) . A promising , alternative approach would be to perform a principal component analysis ( PCA ) decomposition of the snapshots within each model Figure 11 . Visibility amplitude and closure phase residuals for an SSM fit to the April 5 , high - band data for a " good " snapshot image frame from a MAD simulation with a * =0 , i=167 ° , and R high =160 . The reduced - χ 2 values for the fits are 5.9 ( THEMIS ) and 7.3 ( GENA ) . All residuals are normalized by their corresponding estimated observational errors . Figure 12 . Three sample SSM fits to April 6 high - band data . All are from models with THEMIS - AIS p AIS >0.1 . In panels ( a ) and ( b ) , the prominent photon ring places a strong constraint on θ g . In panel ( c ) , the extended disk emission results in a smaller θ g estimate . ( Medeiros et al . 2018 ) , and fit images generated by varying the weights of the PCA components to the data to mimic the set of possible realizations of the turbulence .