On April 10, 2019, major media outlets published the first "image" of a black hole. Astronomy professionals had been awaiting the event: although the image had been captured back in April 2017, it took more than a year to process a colossal volume of data and computations. Producing this image of the black hole at the center of the giant elliptical galaxy M87 required a host of technological innovations, foremost among them the Event Horizon Telescope (EHT).
The "photograph of the black hole" is not an optical snapshot, but a false-color reconstruction of an object some fifty-five million light-years away. Optical astronomy uses lenses and mirrors. Radio astronomy works with antennas—dishes several dozen meters across—and relies on Fourier-analysis techniques to produce an image.
Several radio telescopes had to be brought together because the objects being observed are extremely distant and beyond the reach of optical instruments. Eight radio telescopes are used to increase the effective size of the antenna array and improve resolution; this is radio interferometry. The signals must then be synchronized using a highly accurate clock before being digitized and processed. To complicate matters further, the resulting data streams are enormous—around 8 Gbit/s—and therefore cannot be transmitted over networks…
The evolution of astronomical observation
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Since time immemorial, astronomers have observed the sky and its objects with their own eyes; from Galileo's time onward, they have used optical instruments. In the 20th century, radio astronomy broadened the scope of observation by extending the observable spectrum to include radio waves.
