What Happens When Two Black Holes Orbit Each Other?

So, today in the shower (the true source of inspiration for all of life's mysteries), I was thinking about Black Holes. I don't know why, I just was.

And I got to thinking about how black holes would interact with each other should they begin to orbit each other.

One of the things that struck me was how it would become possible for the center of mass to shift to being outside of the black hole's event horizon. From far away, an object will be drawn to the center of the two holes - and not to any individual hole in particular.

Given a close enough orbit, or large enough black hole, the center of gravity could actually have a stronger net strength than the escape velocity of light. But how would this change things?

It's an odd idea. On the one hand, this is just an apparent center, this is a point which both orbit (which is like two objects circling a stronger 3rd) - but that point has no mass. If that center point has a strength greater than light, then what happens?

On the one hand, I'm tempted to think that a new, 0-mass black hole could form, or that perhaps this is the point where the two holes merge into one (the net force between them being greater than any single one on its own).

On the other hand, I can't help but think that this is the long sought worm-hole - a point that rips/tears space-time, but without mass so as to not rip light or matter that passes through it.

I don't know, and so I'd love to hear some speculation on this. Thanks.

Originally posted by Yarium
So, today in the shower (the true source of inspiration for all of life's mysteries), I was thinking about Black Holes. I don't know why, I just was.

And I got to thinking about how black holes would interact with each other should they begin to orbit each other.

There will be gravitational waves generated, of course.

Given a close enough orbit, or large enough black hole, the center of gravity could actually have a stronger net strength than the escape velocity of light. But how would this change things?

It's an odd idea. On the one hand, this is just an apparent center, this is a point which both orbit (which is like two objects circling a stronger 3rd) - but that point has no mass. If that center point has a strength greater than light, then what happens?

You'd have to do some real difficult math to figure it out, in all honesty. However, I find a slight flow of logic in your Gedanken experiment. You see, the effective size of the combined binary "star" would be larger than the schwarzschild radius for the combined mass. Objects drawn to the center of mass won't be crossing the event horizon of that center.

So nothing spectacular would happen. Of course, if you keep adding mass to the two BHs, the configuration will become more complex. For one, the two will no longer be spherically symmetric. At some point the center of mass will be inside the combined BH. I don't possess expertise or experience to do relevant calculations.

So long as they're orbiting far enough apart that the results of their orbiting doesn't rob them of angular momentum via gravitational waves, they'll just keep going on their merry way around one another. However, if they get too close to one another, they eventually spiral into each other and coallesce, forming a hole with double the mass. But the Schwarzchild radius of the new hole is more than double the size of either old hole or their combination. What happens to the singularities is anyone's guess, however it's believed they combine together to form one singularity. This would happen extremely quickly, it would look almost instantaneous if you could witness it. A massive amount of gravitational energy would also be emitted from their coallescence, that you could detect if you had the right instruments.

I think, from memory, they've determined that if you could hear the sound of the gravitational waves coming from coallescing black holes, it would be equivalent to 2 octaves lower than low C. Sort of like a low rumble, but at very high decibels. Low pitch but very loud.

you'll go through time said my science teacher in grade 8

Originally posted by levis 501
you'll go through time said my science teacher in grade 8

Your teacher isn't correct. You won't go through time, even if you cross a black hole's event horizon. For you, time is still running at the same pace, relative to your own point of view. To an observer outside the hole, your time looks as if it is slowing down to a stop, and appears to stop to them just when you're about to cross the event horizon. From your point of view, time outside speeds up till just when you cross the event horizon, then time outside is going at "infinite" speed.....everything "happens" at once. But to the observer outside the hole, their time is still normal relative to their own point of view. The only point in the hole where things would change drastically is when you get to the singularity. There time as we know it has no meaning and you'd be crushed into oblivion anyway.

So if you were to orbit around the centre of mass of two orbiting black holes about the only thing you'd encounter is gravitational stress and a weird looking view due to massive gravitational lensing. You may also suffer enhanced levels of radiation as well. Especially if you were orbiting closely to the holes.

Any chance the combining of two black holes would simply not work, therefore cancelling eachother out.

Even more worrying, could this destabilize the fabric of space? Cause a Big Crunch? You have me slightly worried now lol.

Like mentioned before, they would produce gravitational waves like other orbiting high mass objects. As for that time travel effect, it was theorized that a doughnut shaped black hole would apply force equally on all sides and propel you at *faster* than the speed of light.....which is totally NUTS for any rational thinking physists. It does seem sound that you could try and go through the center, but as with much we assume about black holes, it is but guesswork and dreaming.