On April 10, 2019, the Event Horizon Telescope (EHT) collaboration published the first image of a black hole: the supermassive black hole at the center of the galaxy M87, showing a bright ring roughly 40 microarcseconds across encircling a dark central shadow. The results appeared as a six-paper focus issue in The Astrophysical Journal Letters, with the lead paper as ApJL 875 L1.
The image was not a photograph but a reconstruction. The EHT links radio dishes around the planet into an Earth-sized virtual telescope through very-long-baseline interferometry, which samples only sparse pieces of the data needed to form an image. Turning that sparse data into a picture is a hard inverse problem with many possible solutions, so the team leaned on computational imaging. Paper IV (arXiv:1906.11241) describes how four teams, each blind to the others, independently reconstructed the source using two distinct approaches: the established CLEAN algorithm and newer regularized maximum likelihood (RML) methods that fit an image while penalizing implausible structure. The ring survived across all teams and both methods, which is what let the collaboration trust the feature was real rather than an artifact.
The reconstruction pipelines were validated against synthetic data and competing parameter choices to guard against shared human bias - an early, high-profile case of algorithmic image reconstruction underpinning a major scientific result.