BH has gone quiet.

[Owen Smith]

did you peek at the answer?

Yes. If they're in circular orbits 1AU apart I'm not surprised it's that long, there needs to be a mechanism for them to lose orbital energy to spiral in. I wonder what it is? Hawking radiation seems unlikely for 40 solar mass black holes.

 

[SemiRamis]

it's counterintuitive at least. Two objects so much heavier than the sun at earth distance which is nothing on astronomical scale take such an inordinate amount of time.
Statistics says it's never happened

 

[Owen Smith]

it's counterintuitive at least. Two objects so much heavier than the sun at earth distance which is nothing on astronomical scale take such an inordinate amount of time.
Statistics says it's never happened

Unless some force is acting on them to change their orbits it is an entirely stable situation and they should never merge or even change orbit at all. Clearly there is some effect that causes their orbits to change that I'm not aware of. Frame dragging or some other effect of General Relativity?