First M87 Event Horizon Telescope Results. II. Array and Instrumentation

Abstract

The Event Horizon Telescope (EHT) is a very long baseline interferometry (VLBI) array that comprises millimeter-and submillimeter-wavelength telescopes separated by distances comparable to the diameter of the Earth. At a nominal operating wavelength of ∼1.3 mm, EHT angular resolution (λ/D) is ∼25 μas, which is sufficient to resolve nearby supermassive black hole candidates on spatial and temporal scales that correspond to their event horizons. With this capability, the EHT scientific goals are to probe general relativistic effects in the strong-field regime and to study accretion and relativistic jet formation near the black hole boundary. In this Letter we describe the system design of the EHT, detail the technology and instrumentation that enable observations, and provide measures of its performance. Meeting the EHT science objectives has required several key developments that have facilitated the robust extension of the VLBI technique to EHT observing wavelengths and the production of instrumentation that can be deployed on a heterogeneous array of existing telescopes and facilities. To meet sensitivity requirements, high-bandwidth digital systems were developed that process data at rates of 64gigabit s −1 , exceeding those of currently operating cm-wavelength VLBI arrays by more than an order of magnitude. Associated improvements include the development of phasing systems at array facilities, new receiver installation at several sites, and the deployment of hydrogen maser frequency standards to ensure coherent data capture across the array. These efforts led to the coordination and execution of the first Global EHT observations in 2017 April, and to event-horizon-scale imaging of the supermassive black hole candidate in M87.

Shadow and quasinormal modes of a rotating loop quantum black hole

“…The calculations of the shadow size and shape, and their observational implications from different black hole spacetimes or spacetimes of compact objects with exotic matters ether in general relativity or in modified theories of gravity have been extensively studied, see, for example, . Recently, the first observational data of the shadow image captured by EHT [1][2][3][4][5][6] have been used for constraining the black hole parameters and deviations from the Kerr metric [49][50][51][52][53]. Although these constraints are still not stringent enough, these works do show that the observational data does have the capacity for constraining black hole parameters beyond those presented in GR.…”

Lensing by Kerr black holes

“…With the advent of horizon-scale observations of astrophysical black holes [1][2][3][4][5][6], the intricate properties of null geodesics in the Kerr spacetime [7][8][9][10][11] are fast becoming a matter of practical relevance to astronomy. Thanks to ray-tracing codes now operating with exquisite accuracy and speed [12][13][14], determining the observational appearance of a specified emission model is a quick and routine task.…”

Photon emission near Myers-Perry black holes in the large dimension limit

“…from which we see that the difference between I φ(1) and I φ (2) only comes from the integration constant. Matching I φ n = I φ f in the overlap region we find…”

“…The first image of the supermassive black hole at the centre of the galaxy M87, was observed by the Event Horizon Telescope (EHT) recently [1][2][3][4][5][6], which opens another new window to the study of black holes apart from gravitational wave detectors such as LIGO and Virgo. Owing to the development of new techniques in the future, the EHT is expected to give more accurate data and thus takes our understanding of black holes to a higher level experimentally.…”