There’s a monster deep in the heart of the Milky Way Galaxy. Even though we can’t see it, we know it’s there ... because it has to be.
Over two decades, astronomers have pointed very large telescopes, including The Very Large Telescope, toward the galactic centre. They’ve been tracking the motions of a bunch of stars right at the core — ordinary stars doing something extraordinary. They’re moving fast, very very fast, in orbit around something very massive. But when astronomers look to find what’s at the centre of these stars’ orbits ... there’s nothing there.
The only real possibility is that they are orbiting a super-massive black hole.
At their fastest, some of the stars are moving at a few percent of the speed of light, which is fast enough to put Einstein’s theory of relativity to the test.