How can you prove that a supermassive black hole exists?
The key to proving that there’s a black hole is showing that there’s a tremendous amount of mass in a very small volume. And you can do that with the motions of stars. The way the star moves around the center of the galaxy is very much like the way the planets orbit the sun. And the planets orbiting the sun can actually [help you] measure the mass of the sun, just the way the stars orbiting the center of the galaxy can tell you what the mass is inside their orbit. So you need to measure stars as close to the center to show that there’s a lot of mass inside a small volume, which is the key to proving the existence of a supermassive black hole.
