Orbiting pair of black holes proves to be triplets

Science : If two black holes orbit close enough to each other, they are predicted to generate gravity waves that should be detectable. The only known close pair are 24 light-years apart, which is not close enough. Now, Roger Deane of the University of Cape Town in South Africa and his colleagues have found a pair orbiting 450 light-years from each other, making them the second closest known pair. Deane’s group had been examining a quasar known to have two black holes orbiting 24 000 light-years apart. They used a radio telescope array to look at the black holes more closely, which is how they discovered that one of the two was a binary system itself. That there is now another known closely orbiting pair of black holes suggests that they might not be as rare as previously thought. Which means that finding a pair that are close enough to generate gravity waves may not be as unlikely.