eht

The Event Horizon Telescope (EHT) is an international collaboration that operates a global very long baseline interferometry array to image the immediate surroundings of supermassive black holes. By combining data from radio dishes around the world, the EHT achieves angular resolution sufficient to resolve event-horizon-scale structures at millimeter wavelengths, notably at 1.3 millimeters (230 GHz).

The project was developed in the early 2010s and links facilities across North America, South America, Europe, and Antarctica, including ALMA and APEX in Chile, JCMT and SMA in Hawaii, NOEMA and IRAM 30m in Europe, LMT in Mexico, SMT in Arizona, and the South Pole Telescope in Antarctica. Observations are conducted in coordinated campaigns; data are recorded on high-capacity storage and shipped to central correlators for processing.

Key results include the 2019 release of the first direct image of a black hole’s shadow, from the supermassive object in the galaxy M87 (M87*). In 2022, the collaboration released an image of Sagittarius A*, the black hole at the center of the Milky Way. These observations test general relativity in strong gravity regimes and inform models of accretion and jet formation.

Methodologically, the EHT relies on very long baseline interferometry, combining signals from widely separated telescopes to synthesize a telescope the size of Earth. Imaging requires complex calibration, modeling, and multiple independent reconstructions to verify features.

Future directions include expanding the network, increasing bandwidth and sensitivity, and observing additional targets and wavelengths, enabling higher-fidelity imaging and time-domain studies of black holes.