https://motherboard.vice.com/en_us/article/vbj3y4/astronomers-confirm-einsteins-theory-of-relativity-by-watching-a-star-orbit-a-black-hole

The closest supermassive black hole to Earth is a mere 26,000 light years away, situated right in the middle of our galaxy. In May, astronomers at the European South Observatory (ESO) in Chile observed a star called S2 make its closest pass by the black hole and got to observe how the intense gravitational field affected the star’s motion. By studying S2 while it made its pass, the astronomers were able to confirm a crucial prediction of Einstein’s general theory of relativity by turning nature into a readymade gravitational laboratory.

With a mass four million times greater than our Sun, the Milky Way’s largest supermassive black hole holds the title for the strongest gravitational field in the galaxy. Extreme conditions are the norm here and any stars that get caught in its gravitational field will orbit the black hole at millions of miles per hour. These extreme gravity conditions make the black hole an ideal place to test theories of gravitational physics, such as Einstein’s theory of general relativity.