The MASSIVE Survey, which is a study of huge galaxies, determined this particular black hole's size by measuring the movements of stars within its influence using the Gemini Observatory telescopes in Hawaii and Chile. Lead astronomer Chung-Pei Ma said the stars were moving so fast that the only possible explanation is that they're affected by a region with "a 17-billion-solar-mass black hole at the center."

It's still a mystery why it's so big, but one possibility is that it's a product of two black holes that merged when their galaxies smashed into each other. Whatever the reason is, scientists now know that supermassive black holes can exist within smaller groups of galaxies. And since that type of cosmic community is more abundant than densely populated ones, then there might be a lot more supersize black holes than we thought.