Event Horizon Telescope

Event Horizon Telescope
Name	Event Horizon Telescope
Organization	Harvard-Smithsonian Center for Astrophysics, Max Planck Institute for Radio Astronomy, MIT Haystack Observatory, ALMA, IRAM, National Radio Astronomy Observatory
Location	Global array
Wavelength	Radio (millimeter)

Event Horizon Telescope. It is a global network of synchronized radio telescopes and interferometry arrays that combines data from multiple very-long-baseline interferometry stations. This creates a virtual telescope with an effective diameter roughly equal to that of Earth, achieving unprecedented angular resolution. The primary objective is to directly observe the immediate environment of supermassive black holes, specifically their event horizons and related phenomena.

Overview

The concept builds upon decades of advancement in very-long-baseline interferometry, pioneered by institutions like the MIT Haystack Observatory and the Max Planck Institute for Radio Astronomy. By synchronizing observations across continents using atomic clocks, the network synthesizes an aperture capable of resolving structures at the scale of a black hole's Schwarzschild radius. This international effort involves leading observatories such as the Atacama Large Millimeter Array in Chile and the South Pole Telescope in Antarctica.

Scientific goals and targets

The foremost goal is to capture the first direct images of a black hole's event horizon and its shadow against the glowing accretion disk. Key targets include Sagittarius A*, the supermassive black hole at the center of the Milky Way, and the much larger black hole in the Messier 87 galaxy. Observations aim to test predictions of Einstein's general relativity in extreme gravity, study relativistic jet formation, and investigate plasma dynamics in these environments. The collaboration also probes the nature of compact objects like Sgr A*.

Technical specifications and array

The network operates at a short millimeter wave wavelength of 1.3 mm (230 GHz), which can penetrate the interstellar dust surrounding galactic cores. Core participating facilities include the Atacama Large Millimeter Array, the IRAM 30-meter telescope on Pico Veleta, the James Clerk Maxwell Telescope on Mauna Kea, the Large Millimeter Telescope on Sierra Negra, and the Submillimeter Array in Hawaii. Data correlation is performed at the MIT Haystack Observatory and the Max Planck Institute for Radio Astronomy using specialized heterodyne receivers and hydrogen maser clocks for timing.

Observations and results

The first major observing campaign occurred in April 2017, with telescopes from the South Pole to Spain collecting data on both Sagittarius A* and Messier 87. In April 2019, the collaboration released the first-ever image of a black hole, revealing the ring-like structure and central shadow of the supermassive black hole in Messier 87. This result, analyzed using algorithms like CHIRP, provided strong evidence for the existence of event horizons and was consistent with general relativity predictions. Subsequent observations have continued to study the dynamics and magnetic field structure around these objects.

Collaboration and funding

The effort is a collaboration of over 300 researchers from more than 80 institutions across the globe. Major funding and support come from the National Science Foundation, the European Research Council, the Japan Society for the Promotion of Science, and agencies like the Chinese Academy of Sciences. Key partner organizations include the Harvard-Smithsonian Center for Astrophysics, the University of Arizona, and the Academia Sinica Institute of Astronomy and Astrophysics in Taiwan.

Future developments

Plans include expanding the array with new telescopes like the Greenland Telescope and the Kitt Peak 12-meter antenna to improve image fidelity. Upgrades to existing facilities, such as the Northern Extended Millimeter Array, and observations at new frequencies aim to produce sharper images and even movies of black hole dynamics. Long-term ambitions involve adding space-based elements to extend the baseline beyond Earth's diameter, a concept studied by missions like the proposed Black Hole Explorer.

Category:Radio telescopes Category:Astronomical imaging Category:Black holes Category:International scientific collaborations