In 2019, the Event Horizon Telescope (EHT) showed the world for the first time an image of the shadow of a black hole - an object whose gravity is so strong that it does not even let light escape. This photo became one of the most recognizable scientific images of our time. Now a group of four researchers from the Australian scientific agency CSIRO has developed a new way of processing data that independently confirmed that very picture. The work was published in the journal Nature.
CSIRO astronomer and lead author of the work Samuel Lai compared the difficulty of the task to trying to photograph a donut lying on the Moon while standing in one's own backyard. Indeed, to make out such a distant object, a telescope the size of a planet is needed. Building one is impossible, so the EHT combines many ground-based antennas around the world: together they work as a single giant instrument. This method is called very long baseline radio interferometry - essentially, the simultaneous observation of one object by many separated telescopes.
However, with this approach the image has to be reconstructed mathematically, and calibration errors or subjective decisions during processing can distort the result. To reduce this risk, the CSIRO team used machine learning and artificial intelligence algorithms. An important detail: the model did not know what a black hole looks like when it was applied to the M87 data. Nevertheless, the reconstructed image turned out to be almost identical to the historic picture in size and shape.
"This is the first truly independent check of the EHT image," Lai noted. According to him, the new approach uses not pairs but triples of telescopes, which makes it possible to eliminate errors and bias. As a result, the researchers became more confident that the ring around the central black hole in M87 is a real astrophysical structure and not a processing artifact.
EHT collaboration director Laurent Loinard called the work important for the scientific process: the independent GenDIReCT method reconstructed the ring structure of M87* over several years of observations, which is in good agreement with the published results. In his opinion, such studies increase confidence in knowledge about black holes.
The authors also suggest that the developed method could be useful outside astronomy - for example, in medical imaging or in mapping earthquakes. However, these are only potential directions, not proven applications.