It’s been more than a decade since the EHT’s bold imaging plans were first begun. In this way, the EHT is able to achieve unprecedented resolution: it can theoretically resolve down to 25 millionths of an arcsecond at its observing wavelength of 1.3 mm. The EHT works by performing very-long-baseline interferometry by combining different telescopes around the world, the EHT can function like a telescope with an effective size that’s the same as its longest baseline - the distance between component telescopes.

For the images of M87 released today, the observations were made by eight ground-based telescopes in Arizona, Hawai’i, Mexico, Chile, Spain, and the South Pole. The EHT is an extensive virtual telescope created by combining simultaneous observations from radio arrays and dishes all around the planet. The eight stations of the EHT 2017 campaign over six geographic locations. So how do we zoom in on this distant object? We need a telescope unlike any other. These factors contribute to making the neighboring behemoth in M87 comparatively accessible for imaging - and, consequently, it’s the first source for which the EHT is presenting images. We’re also peering through much less of the interstellar medium when pointed at M87. M87 may be further away, but its black hole is a thousand times larger than Sgr A*, giving it longer and more manageable variability timescales. This monster’s rapid variability and its position in the galactic plane - where it’s blurred by the interstellar medium - provide additional challenges that must be overcome to accurately capture it. Sgr A*, while the nearest supermassive black hole, suffers from a host of complicating factors for imaging. When astronomers first developed a plan to image a supermassive black hole’s event horizon - the close-in boundary from which not even light can escape - two sources were selected as targets: the black hole at the center of our galaxy, Sgr A* and the gargantuan, jet-producing black hole in the neighboring galaxy M87. Obtaining an up-close view of a black hole is a goal that has long remained out of reach. 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.Hubble image of the elliptical galaxy M87, dominated by the visible jet extending to the northwest of the supermassive black hole at the galaxy’s center (click to enlarge). 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 103-105 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.

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. We present the first Event Horizon Telescope (EHT) observations of Sagittarius A* (Sgr A*), the Galactic center source associated with a supermassive black hole.

First data from event horizon telescope