Event Horizon Telescope

The Event Horizon Telescope (EHT) is an initiative to use radio telescopes around the world to study the supermassive black hole (SMBH), Sagittarius A* at the galactic center of the Milky Way, using Earth-sized VLBI, by resolving the black hole's event horizon. A second black hole, M87* (at the center of galaxy M87) is also a target, as well as other objects for both calibration and study, as the project progresses. Images are collected about once a year when the geometry is right to view the targets so as to collect data subject to the intended interference. The effort aims for baselines in multiple directions on the order of 12000 km, as large as can be done from the ground, and appropriate telescopes are recruited each year toward reaching this goal. The first image was taken in 2006 and the first image that succeeded in detecting one of the black hole shadows (of M87*) was taken in 2018 and announced in 2019 after analysis of the image revealed the shadow. In 2022, such an image of Sagittarius A*'s black hole shadow was announced. In subsequent years, more images of the two have been captured, including some images revealing their magnetic fields through polarimetry.

In 2019, an effort termed ngEHT received initial funding, to expand and upgrade the ENG, to double the number of sites and observe at an additional lower frequency.