# The Naked Scientists Forum

### Author Topic: The 2 black hole problem  (Read 1191 times)

#### jeffreyH

• Global Moderator
• Neilep Level Member
• Posts: 3929
• Thanked: 55 times
• The graviton sucks
##### The 2 black hole problem
« on: 01/01/2015 23:48:48 »
If we had two black holes equal in every respect orbiting each other with and object directly between then at the same radial distance from each one and in a direct line between both centres of gravity what would happen to that object?

#### evan_au

• Neilep Level Member
• Posts: 4131
• Thanked: 249 times
##### Re: The 2 black hole problem
« Reply #1 on: 02/01/2015 10:13:17 »
If the black holes were fairly close to each other, the central object would be torn apart by tidal forces.

Assuming the black holes are far enough apart, and not rotating, and the central object is exactly stationary on the center of mass of the system, then this is a solution of the "3 body problem". However, it is an unstable solution, and any small motion away from this configuration will accelerate.

Barring outside influences, the system could stay like this until gravitational radiation causes the black holes to move close enough together to tear the central object apart.

I expect that with most configurations of rotating black holes,  "frame dragging" will make the solution unstable.

#### evan_au

• Neilep Level Member
• Posts: 4131
• Thanked: 249 times
##### Re: The 2 black hole problem
« Reply #2 on: 02/01/2015 10:19:09 »
The mathematician Lagrange discovered five solutions to the "3 body problem" for the case with Newtonian gravity (Relativity had not yet been invented).

The general problem here is to find the libration points for the relativistic case where at least one of the objects is a black hole.

Note: It will be simpler if we assume black holes with no electric charge.

#### The Naked Scientists Forum

##### Re: The 2 black hole problem
« Reply #2 on: 02/01/2015 10:19:09 »