Remember that first picture of a black hole in our galaxy? We took it

Black holes are among the most profound predictions of Einstein’s theory of general relativity. Originally studied as a mere mathematical consequence of the theory rather than as physically relevant objects, they soon became thought of as generic and sometimes inevitable outcomes of the gravitational collapse that initially forms a galaxy. In fact, most physicists have suspected that our own galaxy revolves around a supermassive black hole at its center. There are other ideas too –