Event Horizon Telescope

[1][2] The Event Horizon Telescope project is an international collaboration that was launched in 2009[1] after a long period of theoretical and technical developments.

[11] The first image of a black hole, at the center of galaxy Messier 87, was published by the EHT Collaboration on April 10, 2019, in a series of six scientific publications.

In March 2021, the Collaboration presented, for the first time, a polarized-based image of the black hole which may help better reveal the forces giving rise to quasars.

[16] The EHT is composed of many radio observatories or radio-telescope facilities around the world, working together to produce a high-sensitivity, high-angular-resolution telescope.

Through the technique of very-long-baseline interferometry (VLBI), many independent radio antennas separated by hundreds or thousands of kilometres can act as a phased array, a virtual telescope which can be pointed electronically, with an effective aperture which is the diameter of the entire planet, substantially improving its angular resolution.

[18] Each year since its first data capture in 2006, the EHT array has moved to add more observatories to its global network of radio telescopes.

[17][20] Studies have previously tested general relativity by looking at the motions of stars and gas clouds near the edge of a black hole.

[32] Relativity predicts a dark shadow-like region, caused by gravitational bending and capture of light,[5][6] which matches the observed image.

The published paper states: "Overall, the observed image is consistent with expectations for the shadow of a spinning Kerr black hole as predicted by general relativity.

Ho, EHT Board member, said: "Once we were sure we had imaged the shadow, we could compare our observations to extensive computer models that include the physics of warped space, superheated matter, and strong magnetic fields.

[43] In August 2022, a team led by University of Waterloo researcher Avery Broderick released a "remaster[ed]" version of original image generated from the data collected by the EHT.

In July 2021, high resolution images of the jet produced by the supermassive black hole sitting at the center of Centaurus A were released.

With a mass around 5.5×107 M☉, the black hole is not large enough for its photon sphere to be observed, as in EHT images of Messier M87*, but its jet extends even beyond its host galaxy while staying as a highly collimated beam which is a point of study.

Observations reveal a helically bent jet and the polarization of its emission suggest a toroidal magnetic field structure.

NRAO 530 (1730−130, J1733−1304) is a flat-spectrum radio quasar (FSRQ) that belongs to the class of bright γ-ray blazars and shows significant variability across the entire electromagnetic spectrum.

The team reconstructed the first images of the source at 230 GHz, at an angular resolution of ~20 μas, both in total intensity and in linear polarization (LP).

A schematic diagram of the VLBI mechanism of EHT. Each antenna, spread out over vast distances, has an extremely precise atomic clock . Analogue signals collected by the antenna are converted to digital signals and stored on hard drives together with the time signals provided by the atomic clock. The hard drives are then shipped to a central location to be synchronized. An astronomical observation image is obtained by processing the data gathered from multiple locations.
EHT observations during its 2017 M87 multiwavelength campaign decomposed by instrument from lower (EHT/ALMA/SMA) to higher (VERITAS) frequency. (Fermi-LAT in continuous survey mode) (dates also in Modified Julian days )
Soft X-ray image of Sagittarius A* (center) and two light echoes from a recent explosion (circled)
A series of images descriptive of the level of magnification achieved by the EHT (akin to seeing, from the Earth's surface, an object the size of a tennis ball on the Moon); starts at top-left image and moves counter−clockwise to finish at top-right corner
Image of M87* generated from data gathered by the Event Horizon Telescope [ 25 ] [ 26 ]
A view of M87* black hole in polarised light
EHT image of the archetypal blazar 3C 279 showing a relativistic jet down to the AGN core surrounding the supermassive black hole.
Image of Centaurus A showing its black hole jet at different scales
A multifrequency view of the bent jet in Blazar J1924-2914. [ 55 ] [ 56 ]
NRAO 530 by EHT. The total intensity is shown in grayscale with black contours indicating 10%, 25%, 50%, and 75% of the peak LP intensity. Black dotted contours indicate 25%, 50%, and 75% of the peak polarized intensity.
Schematic of the total-intensity and LP components in the EHT fiducial image of NRAO 530; white contours show the total intensity levels; color scale and cyan contours represent the polarized intensity of the method-averaged image.
Locations of the telescopes that make up the EHT array. A global map showing the radio observatories that form the Event Horizon Telescope (EHT) network used to image the Milky Way’s central black hole, Sagittarius A*. The telescopes highlighted in yellow were part of the EHT network during the observations of Sagittarius A* in 2017. These include the Atacama Large Millimeter/submillimeter Array (ALMA), the Atacama Pathfinder EXperiment (APEX), IRAM 30-meter telescope (30-M), James Clark Maxwell Telescope (JCMT), Large Millimeter Telescope (LMT), Submillimeter Array (SMA), Submillimetere Telescope (SMT) and South Pole Telescope (SPT). Highlighted in blue are the three telescopes added to the EHT Collaboration after 2018: the Greenland Telescope (GLT), the NOrthern Extended Millimeter Array (NOEMA) in France, and the UArizona ARO 12-meter Telescope at (Kitt Peak}.