However, one can hope that the future development of precise astronomical instruments (e.g., at the facilities of the Event Horizon Telescope) will accurately measure the orbital precession of the pericentres of the known S-stars and of other, at present unobserved, more short-period stars. Thus, we will be able to recognize observationally the nature of the object Sgr A\*.

[9]{}

L. Meyer et al, The shortest known period star orbiting our galaxy’s supermassive black hole. Science **338**, 6103, 84–87 (2012) [arXiv:1210.1294](https://arxiv.org/abs/1210.1294)

K. Akiyama et al, 230 GHz VLBI observations of M87: event-horizon-scale structure at the enhanced very-high-energy $\gamma$-ray state in 2012. Astrophys. J. **807**, 150 (2015) [arXiv:1505.03545](https://arxiv.org/abs/1505.03545)

V.L. Fish et al, Persistent Asymmetric Structure of Sagittarius A\* on Event Horizon Scales. Astrophys. J. **820**, 90 (2016) [arXiv:1602.05527](https://arxiv.org/abs/1602.05527)

S. Gillessen et al, An update on monitoring stellar orbits in the galactic center. Astrophys. J. **837**, 30 (2017) [arXiv:1505.03545](https://arxiv.org/abs/1611.09144)

C. Goddi et al, BlackHoleCam: fundamental physics of the Galactic center. Int. J. Mod. Phys. D **26**, 1730001 (2017) [arXiv:1606.08879](https://arxiv.org/abs/1606.08879)

A. Hees et al, Testing General Relativity with stellar orbits around the supermassive black hole in our Galactic center. Phys. Rev. Lett. **118**, 211101 (2017) [arXiv:1705.07902](https://arxiv.org/abs/1705.07902)

P.S. Joshi, D. Malafarina, R. Narayan, Distinguishing black 