Trajectories of Bright Stars and Shadows around Supermassive Black Holes as Tests of Gravity Theories

Abstract

General relativity (GR), created more than a century ago, has been checked in various experimental and observational tests. At an early stage of its development, GR predictions were tested in problems where the gravitational field is weak and relativistic corrections can be considered as small perturbations of the Newtonian theory of gravity. However, in recent years due to the progress of new technologies it turned out to be possible to verify the predictions of GR in the limit of a strong gravitational field, as it was done to verify predictions about the profile of the X-ray line of iron Kalpha , estimates of the gravitational wave signal during the mergers of binary black holes and/or neutron stars and during the reconstruction of the shadows of black holes in Sgr A* and M87*. Groups of astronomers using the Keck and VLT (GRAVITY) telescopes confirmed the GR predictions for the redshift of the spectral lines of the S2 star near the passage of its pericenter (these predictions were done in the first post-Newtonian approximation). It is expected that in the near future, observations of bright stars using large telescopes VLT (GRAVITY), Keck, E-ELT and TMT will allow us to verify the predictions of GR in the strong gravitational field of supermassive black holes. Observations of bright stars in the vicinity of the Galactic Center and reconstructions of the shadows of black holes allow not only to verify the predictions of the GR, but also to obtain restrictions on alternative theories of gravity.