M33 X-7 binary star system, computer artwork. M33 X-7 is located in M33, a galaxy 2.6 million light years from Earth. It consists of a black hole (its accretion disc can be seen, orange) in orbit with a huge companion star (blue). The black hole is the largest to have formed from a collapsed star. The companion star also has an unusually large mass, 70 times that of the Sun. This makes it the most massive companion star known in a binary system containing a black hole. Material from the companion star is seen being pulled toward the black hole by its powerful gravity. The companion star itself is also distorted by the gravity from the black hole. It is stretched slightly in the direction of the black hole, causing it to become less dense in this region and to appear darker.