https://www.cnet.com/news/astronomers-set-to-make-groundbreaking-black-hole-announcement/

However, at the very edge of a black hole's powerful gravity lies the "event horizon". Material accumulates in this region and speeds around the black hole at such pace that it emits high-energy radiation -- the stuff that we can see. Over the past 13 years, the Event Horizon Telescope (which is actually a network of radio observatories across the planet) has been trying to image two black holes: Sagittarius A*, at the center of the Milky Way, and the black hole at the center of Messier 87, a nearby elliptical galaxy.

The observatories around the world focus on the locations of the black hole and individually capture the radio signals emitted by the event horizon. The data they capture is digitized and stored on hard drives, which are physically flown to participating institutions for analysis. Because each telescope across the world is all synced up to an incredibly precise clock, the data can be correlated, stitched together and eventually -- and this is the holy grail -- produce an image of the black hole's event horizon.