Scientists have described a black hole that's nearly 16 times the mass of the Sun. Dubbed M33 X-7, the enormous object is known as a stellar black hole because it formed after the collapse of the core of a massive star. But scientists say M33 X-7 isn't just interesting because of its size. It's part of a binary system, orbiting a star that's 70 times the mass of the Sun. The two are in a tight orbit: the star eclipses M33 X-7 twice per week. Eventually it will go supernova, exploding outwards and collapsing into a second massive black hole.