How We Actually Photographed a Black Hole (And What It Took)

In April 2019, the Event Horizon Telescope collaboration released the first photograph of a black hole — M87*, a supermassive black hole 6.5 billion times the mass of our Sun, located 55 million light-years away. Two years later, they released the first image of Sagittarius A*, the black hole at the center of our own Milky Way.

Both images look like blurry orange donuts. They are among the most important photographs in human history.

The Engineering Problem

To image a black hole, you need a telescope with angular resolution roughly 1,000 times better than the Hubble Space Telescope. No single dish could be large enough — the required diameter would be larger than Earth itself. The solution: Very Long Baseline Interferometry (VLBI), which links multiple radio telescopes across the globe and combines their signals using the known distance between them as the effective aperture.

The Network

The EHT comprises eight observatories across six continents, including the South Pole Telescope in Antarctica, the Atacama Large Millimeter Array in Chile, and observatories in Hawaii, Spain, Mexico, and Arizona. Together they form a virtual dish the size of Earth, with an angular resolution capable of reading a newspaper in New York from Paris.

The Data Challenge

The EHT generates so much data that it can't be transmitted over the internet — it's physically shipped on hard drives from each observatory. The 2017 observation campaign generated approximately five petabytes of data, flown to correlation centers at MIT Haystack Observatory and the Max Planck Institute in Germany for processing.

What the Image Actually Shows

The bright ring surrounding the dark center (the "shadow" of the black hole) is light from the accretion disk being bent around the black hole by its gravity. The bottom of the ring appears brighter because that side of the disk is rotating toward us, boosting the apparent brightness through relativistic beaming. The dark center is not the black hole itself — it's the region from which light cannot escape, roughly 2.5 times the size of the event horizon.

Sagittarius A* — The Harder Target

Imaging the Milky Way's central black hole was significantly harder than M87*. Despite being much closer (26,000 light-years vs. 55 million), Sgr A* is far less massive and its material orbits it in hours rather than days — meaning the target was visibly changing during the observation window. The 2022 image required sophisticated new algorithms to average the rapidly varying emissions into a coherent picture.