Astronomers Publish the First Image of a Black Hole

On April 10, 2019, the Event Horizon Telescope Collaboration announced the publication of the first direct image of a black hole at coordinated press conferences around the world. The observation captured the supermassive black hole situated at the heart of the elliptical galaxy Messier 87, designated M87*. Detailed in six papers in The Astrophysical Journal Letters, the breakthrough came from an international collaboration of more than 200 researchers, building on decades of foundational theory and technical radio development. By combining observatories across the globe, the project established an effective instrument possessing an angular resolution sharp enough to resolve the silhouette of an event horizon.

Capturing this astronomical feature required the technique of very-long-baseline interferometry, linking independent antennas separated by vast distances into a phased array. Operating as an Earth-sized virtual aperture pointed electronically, the network measured signals at a wavelength of 1.3 millimeters, achieving an angular resolution of about 20 microarcseconds, according to ESO. At each antenna, analogue signals were converted to digital form and stored on hard drives together with time signals from a highly precise atomic clock. Because of extreme data volumes, these drives were transported on commercial aircraft to the MIT Haystack Observatory and the Max Planck Institute for Radio Astronomy, where specialized supercomputers known as correlators combined the information.