EHT

Very-long-baseline interferometryVLBIVery-long-baseline interferometry: telescopes thousands of kilometres apart record signals against atomic clocks and correlate them afterwards. Earth-sized baselines at 1.3 mm give the EHT about 20 µas resolution. at 1.3 mm (230 GHz) and 0.87 mm (345 GHz) between millimetre telescopes on four continents and at the South Pole. Earth-diameter baselinesbaselineThe separation between two antennas of an interferometer, projected onto the plane perpendicular to the source. Long baselines give fine resolution; short ones recover extended emission. give resolution of a few tens of µasarcsecond1/3600 of a degree (″). A milliarcsecond (mas) is 10⁻³″ and a microarcsecond (µas) 10⁻⁶″. Atmospheric seeing limits ground telescopes to about 0.5–1″ without adaptive optics. (19 µas in the first 345 GHz detections, 2024), enough to resolve the emission ring around the shadows of the supermassive black holes M87* (2019) and Sgr A* (2022).

Operator

EHT collaboration

Site

Telescopes on four continents and the South Pole

Aperture

Earth-sized virtual dish

Passband

230 GHz – 345 GHz

First full campaign

April 2017