At the center of our Milky Way galaxy sits a supermassive black hole — which astronomers named Sgr A* — with over 4 million times the Sun's mass.
But it's not alone. Lots of other stuff is there, too, orbiting that black hole, including stars, gas, and dust. Over time, we can see these objects move, held sway by the incredible gravity of Sgr A*. In fact, the motions of several stars have told us a lot about the black hole itself.