They tried using a tape measure, but it kept getting sucked in.
Astronomers have found a way to measure the size of a black hole. Supermassive black holes reside at the center of galaxies and have gravitational forces so strong that nothing, including light, can escape from being pulled into them. By combining the power of radio dishes in three different states into a super-telescope 2,000 times more powerful than Hubble, the astronomers measured the radius of an "accretion disk," or a logjam of matter that forms around a black hole. This doomed mass teeters at the black hole's event horizon, where the physics of space and time begin to break down in the ultimate opportunity to test Einstein's theories of gravity. Currently only verified in less extreme conditions, like here on Earth, popular theories were backed up by the team's black hole measurements.
With more telescopes added to the array in the future, they hope to shed more light, albeit metaphorically, on these gravitational gorgons.