![]() ![]() A variety of imaging and modeling analyses all support an image that is dominated by a bright, thick ring with a diameter of 51.8 ± 2.3 μas (68% credible interval). The EHT data resolve a compact emission region with intrahour variability. These observations were conducted in 2017 using a global interferometric array of eight telescopes operating at a wavelength of λ = 1.3 mm. Furthermore, a comparison with the EHT results for the supermassive black hole M87 * shows consistency with the predictions of general relativity spanning over three orders of magnitude in central mass.Ībstract = "We present the first Event Horizon Telescope (EHT) observations of Sagittarius A* (Sgr A*), the Galactic center source associated with a supermassive black hole. Our results provide direct evidence for the presence of a supermassive black hole at the center of the Milky Way, and for the first time we connect the predictions from dynamical measurements of stellar orbits on scales of 10 3-10 5 gravitational radii to event-horizon-scale images and variability. Our model comparisons disfavor scenarios where the black hole is viewed at high inclination (i > 50°), as well as nonspinning black holes and those with retrograde accretion disks. Using a large suite of numerical simulations, we demonstrate that the EHT images of Sgr A * are consistent with the expected appearance of a Kerr black hole with mass ∼4 × 10 6 M ☉, which is inferred to exist at this location based on previous infrared observations of individual stellar orbits, as well as maser proper-motion studies. The ring has modest azimuthal brightness asymmetry and a comparatively dim interior. These measurements provide the first opportunity to image horizon-scale structure in M87.We present the first Event Horizon Telescope (EHT) observations of Sagittarius A * (Sgr A *), the Galactic center source associated with a supermassive black hole. The M87 data reveal the presence of two nulls in correlated flux density at ~3.4 and ~8.3 Gλ and temporal evolution in closure quantities, indicating intrinsic variability of compact structure on a timescale of days, or several light-crossing times for a few billion solar-mass black hole. They are validated through a series of quality assurance tests that show consistency across pipelines and set limits on baseline systematic errors of 2% in amplitude and 1° in phase. The final data products include calibrated total intensity amplitude and phase information. In response, we developed three independent pipelines for phase calibration and fringe detection, each tailored to the specific needs of the EHT. The observations present challenges for existing data processing tools, arising from the rapid atmospheric phase fluctuations, wide recording bandwidth, and highly heterogeneous array. These global very long baseline interferometric observations include for the first time the highly sensitive Atacama Large Millimeter/submillimeter Array (ALMA) reaching an angular resolution of 25 μas, with characteristic sensitivity limits of ~1 mJy on baselines to ALMA and ~10 mJy on other baselines. We present the calibration and reduction of Event Horizon Telescope (EHT) 1.3 mm radio wavelength observations of the supermassive black hole candidate at the center of the radio galaxy M87 and the quasar 3C 279, taken during the 2017 April 5–11 observing campaign. ![]()
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