Constraining Nonsingular Black Holes with a Minkowski Core via EHT Observations of M87* and Sgr A*

The Event Horizon Telescope (EHT) imaging of M87* and Sgr A* provides a unique opportunity to test spacetime geometries in the strong-field regime. Motivated by this, we systematically investigate the optical characteristics for three types of nonsingular black holes (BHs) with a Minkowski core and constrain the quantum gravity effect parameter α and the regularization parameter n using EHT observational data. Utilizing the observed shadow sizes of M87* and Sgr A*, we conduct a detailed comparison of the constraints on α for the three BH types. Our analysis reveals significant differences among them: Type I BHs exhibit the largest upper limit, whereas Type III BHs show the smallest upper limit. Furthermore, the constraints derived from M87* observations are tighter than those from Sgr A*, reflecting the close dependence of these limits on current observational precision. Subsequently, we simulate BH images at the current EHT resolution using a Gaussian filter. Although the photon ring and lensed ring features cannot be resolved, variations in shadow size and brightness distribution are clearly detectable. Within the parameter space allowed by EHT observations, the shadow size and total intensity exhibit a distinct monotonic hierarchy: Type I BHs display the largest shadow and highest total intensity, while Type III BHs show the opposite trend. Finally, we find that increasing α leads to shadow contraction and dimming, whereas increasing n causes the shadow to expand while making the optical characteristics of the three BH types increasingly indistinguishable. Consequently, the three BH types become more readily distinguishable only when n is small or α is large.