Event Horizon Telescope

The Event Horizon Telescope is a global radio observatory that combines widely separated antennas through very-long-baseline interferometry to resolve structures near black hole event horizons.

Very-long-baseline interferometry: A radio astronomy technique that combines signals from widely separated antennas to achieve the angular resolution of an Earth-sized telescope. It is the technique that lets the array resolve black-hole-scale structures.
Sagittarius A*: The compact radio source at the center of the Milky Way, associated with a supermassive black hole. The EHT produced the first image of its black-hole shadow in 2022.
Black hole: A region of spacetime whose gravity is so strong that nothing, including light, can escape from within its event horizon. The EHT observes emission shaped by black holes, not the black holes themselves.
Black-hole imaging: The observational reconstruction of radiation around a black hole into images of its surrounding structure. The EHT established a new observational approach to studying black holes at horizon scales.
Atomic clock: A clock that measures time using the stable frequency of atomic transitions. Hydrogen maser atomic clocks timestamp each observatory’s recordings for later alignment.
M87*: The supermassive black hole at the center of the galaxy Messier 87. Its 2019 image was the first direct image of a black-hole shadow.
Event horizon: The boundary around a black hole beyond which escape to distant observers is impossible. It gives the telescope its name, though an image does not show the boundary directly.
Black hole test of general relativity: A comparison between black-hole observations and predictions of general relativity in strong gravitational fields. EHT image dimensions and shapes can be compared with relativistic predictions.
Radio interferometry: A method that combines radio signals from multiple antennas to measure a source’s angular structure. It provides the broader measurement framework behind the array’s observations.
Messier 87: A giant elliptical galaxy in the Virgo Cluster, known for a prominent relativistic jet. Its central black hole supplied the EHT’s first imaging target.

Linked from 26 pages