In April of 2017, all 8 of the telescopes/telescope arrays associated with the Event Horizon Telescope pointed at Messier 87. This is what a supermassive black hole looks like, where the event horizon is clearly visible. (EVENT HORIZON TELESCOPE COLLABORATION ET AL.)

10 Deep Lessons From Our First Image Of A Black Hole’s Event Horizon

And what do we still have left to learn?

The original idea of a black hole goes all the way back to 1783, when Cambridge scientist John Michell recognized that a massive enough object in a small enough volume of space would render everything — even light — unable to escape from it. More than a century later, Karl Schwarzschild discovered an exact solution to Einstein’s General Relativity that predicted the same result: a black hole.

Both Michell and Schwarzschild predicted an explicit relationship between the event horizon, or the radius of the region from which light cannot escape, and the mass of the black hole as well as the speed of light. For 103 years after Schwarzschild, this prediction went untested. At long last, on April 10, 2019, scientists revealed the first-ever picture of a black hole’s event horizon. Einstein’s theory won again, as did all of science.

The second-largest black hole as seen from Earth, the one at the center of the galaxy M87, is shown in three views here. At the top is optical from Hubble, at the lower-left is radio from NRAO, and at the lower-right is X-ray from Chandra. Despite its mass of 6.6 billion Suns, it is over 2000 times farther away than Sagittarius A*. The Event Horizon Telescope attempted to view its black hole in the radio, and this is now the location of the first black hole to have its event horizon revealed. (TOP, OPTICAL, HUBBLE SPACE TELESCOPE / NASA / WIKISKY; LOWER LEFT, RADIO, NRAO / VERY LARGE ARRAY (VLA); LOWER RIGHT, X-RAY, NASA / CHANDRA X-RAY TELESCOPE)

Although we already knew plenty about black holes prior to the first direct image of an event horizon, this new release truly does qualify as a game-changer. There were a bunch of questions we had prior to this discovery…