First Sagittarius A* Event Horizon Telescope Results. I. The Shadow of the Supermassive Black Hole in the Center of the Milky Way

Abstract

We present the first Event Horizon Telescope (EHT) observations of Sagittarius A* (Sgr A*), the Galactic center source associated with a supermassive black hole. These observations were conducted in 2017 using a global interferometric array of eight telescopes operating at a wavelength of λ = 1.3 mm. The EHT data resolve a compact emission region with intrahour variability. 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 ring has modest azimuthal brightness asymmetry and a comparatively dim interior. 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 × 106 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. 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. 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. 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.

Horizon-scale tests of gravity theories and fundamental physics from the Event Horizon Telescope image of Sagittarius A$^*$

“…Second, and perhaps most importantly, there is no clear consensus on the value of SgrA * 's spin and inclination angle. The EHT images are in principle consistent with large spin and low inclination angle, but are far from being inconsistent with low spin and large inclination angle [11,15]. Independent works based on radio, infrared, and X-ray emission, as well as millimeter VLBI, exclude extremal spin (1 − a 1), but have been unable to place strong constraints otherwise [149][150][151] constraints across a wide range of spin values [152,153].…”

“…Horizon-scale images of supermassive black holes and their shadows have opened a new unparalleled window onto tests of gravity and fundamental physics in the very strong-field regime, including the possibility that astrophysical BHs may be described by alternatives to the Kerr metric. In this work, we have used the horizonscale images of SgrA * provided by the Event Horizon Telescope [11][12][13][14][15][16][17][18][19][20] to test some of the most popular and well-motivated scenarios deviating from the Kerr metric. Compared to horizon-scale images of M87 * , there are significant advantages in the use of images of SgrA * , as we discussed towards the end of Sec.…”

“…fractal is built around the BH event horizon, modifying its total surface and volume. 11 In this picture, the entropy-area law of a BH is modified as:…”

“…The first groundbreaking SMBH images were delivered by the Event Horizon Telescope (EHT), a millimeter VLBI array with Earthscale baseline coverage [2], which in 2019 resolved the near-horizon region of the SMBH M87 * [3][4][5][6][7][8], before later revealing its magnetic field structure [9,10]. This was recently followed by the EHT's first images of Sagittarius A * (SgrA * ), the SMBH located at the Milky Way center [11][12][13][14][15][16][17][18][19][20].…”

Termination of Superradiance from a Binary Companion

“…Other bounds come from, for example, testing the birefringence of photons [36] and the stellar kinematics [37] near supermassive black holes, with the help of powerful telescopes such as EHT [38,39] and the Keck Observatory [40]. These bounds also assume the presence of cloud, and are subjected to a similar relaxation as mentioned here, since supermassive black holes are known to be surrounded by numerous stars.…”