Is our universe filled with black holes?

Chris Smith put this to Andrew Norton, professor of astronomy at the Open University...

Andrew - Well pretty much, yeah. We always suspected that was the case and we've seen sort of indirect evidence for those blackholes out there. We think there's a super massive blackhole in centre of pretty much every galaxy. But the fact that there are these binary blackholes out there, dead remnants of stars that are orbiting around each other, gradually spiralling together, and then colliding to give us this gravitational wave signature. They must be going on all the time and now, that we've got the sensitivity to detect them, we're going to be picking them up all the time, I'm pretty sure.