Black Hole Shadows Constrain Extended Gravity 2: Sgr A*

Abstract—When the paper V. Prokopov, S. Alexeyev, and O. Zenin, J. Exp. Theor. Phys. 135, 91 (2022) was already published, the Event Horizon Telescope (EHT) obtained the first direct image of a black hole in the center of our galaxy, i.e. Sagittarius A* (see The Event Horizon Telescope Collab., Astrophys. J. Lett. 930 (L17) (2022)). Here we state that the results obtained earlier in the paper V. Prokopov, S. Alexeyev, and O. Zenin, J. Exp. Theor. Phys. 135, 91 (2022) for the Horndesky model with the Gauss-Bonnet invariant, loop quantum gravity, scalar bumblebee model, Gauss–Bonnet gravity and conformal gravity are in the agreement with Sgr A* observations. The new observational data limit the values of the parameter α in f(Q) gravity: –0.025 < α < 0.005. For the alternative generalization of the bumblebee metric with the Schwarzschild approximation, the constraint transfers to –0.05 < l < 0.45. The obtained limits demonstrate the maximum that can be achieved without taking into account the black hole rotation.