Independent interferometric observable confirms black hole shadow in M87*

Abstract A new epoch for direct visualization of accretion dynamics near the event horizon of a black hole began when the Event Horizon Telescope Collaboration synthesized an Earth-sized aperture with millimetre radio interferometry and published the first reconstructed image 1–4 of a black hole shadow at the core of radio galaxy Messier 87 (M87). The image appeared as a ring-like structure, representing the gravitationally lensed and redshifted emission around the central supermassive black hole, M87*, located at the galactic nucleus. However, application of various data analysis and imaging heuristics resulted in divergent representations of M87* fine-scale features 3,5–7 , with some external analyses even challenging the fundamental ring-like morphology of the source 8,9 . Such difficulties arise as a consequence of the inherent sparsity of the very long baseline interferometry measurements, making interferometric image reconstruction an inadequately constrained problem. Moreover, the solution is sensitive to instrument calibration, post-processing algorithms and imaging hyperparameters. Here we apply an independent imaging algorithm that we have developed to the M87* dataset that is free from prescriptive morphological priors and founded on observables immune to instrument calibration errors. We reconstruct the black hole shadow image and unequivocally reproduce a ring-like morphology, with an angular diameter of 42.2 ± 1.5 μas corresponding to a black hole mass of 6.5 ± 0.5 billion solar masses assuming nominal scaling parameters, observed at an inclination angle of approximately 20° from the approaching jet.