The Event Horizon Telescope (EHT) Array
The Event Horizon Telescope (EHT) is a global Very Long Baseline Interferometry (VLBI) collaboration that links millimeter-wavelength observatories across the Americas, Europe, Hawaii, Greenland, and the South Pole. Operating at 230 GHz (λ = 1.3 mm) and 345 GHz (λ = 0.87 mm) across a 10,700-km baseline, the EHT achieves ~15–20 microarcsecond angular resolution—the highest in astronomy—directly resolving the photon rings around M87* and Sagittarius A*.
Physical Mechanism & Dynamics
At centimeter radio wavelengths, synchrotron self-absorption in the accretion flow and interstellar diffractive scattering blur the view of horizon-scale structures. At λ = 1.3 mm (230 GHz) and 0.87 mm (345 GHz), the accretion plasma around M87* and Sagittarius A* becomes optically thin and interstellar scattering drops as λ², unveiling the lensed photon ring at ~5.2 GM/c².
Participating facilities—including ALMA (which acts as a 66-dish phased array providing critical sensitivity), APEX, IRAM 30-m, NOEMA, JCMT, SMA, SMT, LMT, Kitt Peak, Greenland Telescope, and the South Pole Telescope—record petabytes of raw voltage data at 64 Gbps onto helium-sealed hard drives, which are flown to supercomputer correlators at MIT Haystack and MPIfR Bonn.
Quantitatively, this mechanism is governed by EHT Diffraction Limit and Shadow Angular Diameter (θ_EHT ≈ λ / B_max ≈ 20 μas (at 230 GHz) ; d_shadow = 2√27 (GM / c² D)). Upgrading to 345 GHz (λ = 0.87 mm) sharpens the EHT diffraction limit to ~13–15 microarcseconds.
EHT Diffraction Limit and Shadow Angular Diameter
θ_EHT ≈ λ / B_max ≈ 20 μas (at 230 GHz) ; d_shadow = 2√27 (GM / c² D)Upgrading to 345 GHz (λ = 0.87 mm) sharpens the EHT diffraction limit to ~13–15 microarcseconds.
Quantitative Benchmarks & Parameters
| Parameter / Observable | Measured Value / Scale | Method & Context |
|---|---|---|
| Observing frequencies | 230 GHz (1.3 mm) & 345 GHz (0.87 mm) | Optically thin horizon synchrotron window |
| Maximum baseline length | 10,700 km | Earth-diameter aperture synthesis |
| Angular resolution | 15–25 microarcseconds | Equivalent to reading a newspaper in New York from Paris |
| Data recording rate | 64 Gigabits per second per station | Hydrogen-maser synchronized VLBI backends |
Observational Evidence & How Scientists Know
The EHT resolved the 42 ± 3 μas ring of M87* (2019) and the 51.8 ± 2.3 μas ring of Sagittarius A* (2022), plus polarized synchrotron magnetic field spirals around both black holes.
Across reference datasets (Event Horizon Telescope Collaboration Horizon-Scale Results), quantitative benchmarks for the event horizon telescope (eht) array are anchored by: Observing frequencies (230 GHz (1.3 mm) & 345 GHz (0.87 mm), via Optically thin horizon synchrotron window); Maximum baseline length (10,700 km, via Earth-diameter aperture synthesis); Angular resolution (15–25 microarcseconds, via Equivalent to reading a newspaper in New York from Paris); Data recording rate (64 Gigabits per second per station, via Hydrogen-maser synchronized VLBI backends).
Uncertainties, Systematics & Open Questions
Next-generation EHT (ngEHT) and space-VLBI concepts aim to add dedicated dishes and an orbiting antenna to capture real-time movies of Sgr A*'s 30-minute orbital flares and resolve the n = 1 relativistic photon sub-ring.
Real Astronomical Benchmarks & Cross-Domain Links
Sagittarius A*
Milky Way supermassive black hole imaged by the EHT collaboration
EHT Images of M87* & Sgr A*
Scientific results and general-relativity tests from the EHT
Very Long Baseline Interferometry
Interferometric physics underlying the EHT
Guided Learning Path
Related Concepts, Methods & Explorers
Scientific Sources & Provenance
- Event Horizon Telescope Collaboration Horizon-Scale Results (2019 ApJL 875 L1 & 2022 ApJL 930 L12) — Event Horizon Telescope Collaboration 2019, ApJL, 875, L1; 2022, ApJL, 930, L12. Archive / Reference ↗
Have a correction or updated measurement? Review our Epistemic Standards and Corrections Policy.