1. The problem statement, all variables and given/known data In 2009, astronomers found convincing evidence of two such black holes orbiting as a binary system. From data collected, they estimated that the separation of the black holes was 3.2 × 1015 m and that their masses were 1.6 × 1039 kg and 4.0 × 1037 kg. The black holes orbit about a point 7.7 × 1013 m from the larger mass black hole. Show that the orbital time of the binary system is about 100 years. 2. Relevant equations F = GMM / r2 F = Mw2r 2pi/w = T 3. The attempt at a solution I know I have to equate centripetal force to the gravitational force, then substitute the 2pi/w = T to get an expression involving the time period. However I'm just stumped on how to consider the radius in this question.