# Can a binary star system create a stationary black hole?

Research over the last 200 years suggests that half or more of visible stars are part of multiple star systems.

I apologise for the number of assumptions in my question but, because of the numbers of binary systems involved, I feel this "what if" type question may be a plausible physical outcome in some binary star systems.

Assume both stars were born at the same time, with approximately the same mass, but spinning in opposite directions. I don't know enough about stellar evolution to say whether this is feasible, but we do know binary star systems exist and they must have some chance, over time, of reaching similar angular momentum values, occasionally in oppositely rotating directions.

My questions are, assuming they are close enough, will this eventually result in a slowdown in their rotations, followed by mutual tidal locking?

If this occurs, and the mass of at least one star is large enough, could we then have a stationary neutron star or black hole?

I realise that the process of creating the dense star will occur after a supernova explosion, which will most likely vaporise the other star in the system.

I note there are related questions such as Binary Star System but I can't immediately see a duplicate of my question.

• You would expect that the the binary stars formed from a single cloud of gas that had some angular momentum, since they are orbiting each other. Therefore, the binary system would have to maintain that momentum. It would be unlikely that they could combine into something that had zero angular momentum. Jul 24, 2016 at 0:37
• Maybe terminology, but to be clear a black hole with angular momentum is stationary. Without it is static. All after they settle down to their equilibirium states. The stationary case is the Kerr solution, with rotation. The static case is the spherically symmetric nonrotating Schwarzchild black hole. And yes, possible to have zero rotation but highly unlikely because the orbital rotation soon before they collapse is huge, they are accelerating quickly to near c;it requires really fine tuning to make it all come to zero. Simulations do give different specific results for counter to co rotating Jul 24, 2016 at 6:42
• @BobBee thanks Bob, I forgot some basic but important GR terminology.
– user108787
Jul 24, 2016 at 9:29