Abstract：General relativity (GR) has passed every test in our solar system, to date. But there is still a lack of strict tests of GR in the strong gravitional field near the event horizon of black holes. Owling to their proximity, the event horizon of SgrA* and M87* (two massive black holes residing in the center of our Galaxy and the giant elliptical galaxy M87, respectively) have the largest angular sizes in the sky, they are the natural laboratories for studying physics of strong gravitional fields.

At 21:00 on April 10, 2019 (SGT), the first Event Horizon Telescope (EHT) image of M87* was released, which clearly shows the black hole shadow for the first time, and directly demonstrates the existence of black hole in our Universe. In addition, in May 2018, VLTI-Gravity of the European Southern Observatory detected the orbital motions of hot spots near the last stable circular orbit of the SgrA. In this talk, after a very brief introduction to the physics of strong graivtional fields, I will convince you how to use the gas dynamics and radiation around the horizon of SgrA* and M87* to test general relativity in the strong field regime.