Thread: Black Holes and Gravito-Magnetism

So, over in this thread, an interesting physics principle came up:

http://www.thescienceforum.com/What-...ism-16990t.php

Originally Posted by Janus

Originally Posted by kojax

So, as I begin to understand magnetism a little better, I think a better question to have asked would be "what is the equivalence between gravity and the electric force?" Since the magnetic force is caused by a moving charge, it seems the charge itself is the thing to compare gravity with.

But now I wonder something: Does a moving gravitational object create anything that could be compared to the magnetic field created by a moving electric charge?

Yes, it is predicted to do so in GR, it is known generally as gravitomagnetism. More specifically, it is what is responsible for frame dragging. It is, however a very weak effect.

I'm wondering: Does anything prevent a black hole from emitting energy via gravito-magnetism?

I'm thinking that, if the black hole moves at all, then presumably its gravitational field is creating gravito-magnetic fields as well, and a changing gravito-magnetic field would be a means of transferring energy. (At least if gravito-magnetism and ordinary magnetism are similar in this regard)

Does anything stop that from working?

What I'm wondering is whether this provides a mechanism for energy to escape the black hole.

Take a look at this: Gravitational wave

So it seems the collapse of the orbit between 2 objects (such as binary stars) can be (partially) caused by the amount of energy they have radiated into space by creating an alternating gravitomagnetic field.


Interesting link. I see 2 possible interpretations:


1) - The interaction between a black hole at the center of a galaxy and the stars around it probably radiates these kinds of waves, causing the stars to slowly get closer and closer, until they cross the event horizon and are lost forever.

2) - If a black hole at the center of a galaxy ever "wobbles" due to the orbits of the stars (and I'm wondering whether that wobble would be an equal and opposite reaction, because of how gravity works), then the motion of the black hole itself would create gravito magnetic waves that allow energy to escape.

Originally Posted by kojax

So, over in this thread, an interesting physics principle came up:

http://www.thescienceforum.com/What-...ism-16990t.php

Originally Posted by Janus

Originally Posted by kojax

So, as I begin to understand magnetism a little better, I think a better question to have asked would be "what is the equivalence between gravity and the electric force?" Since the magnetic force is caused by a moving charge, it seems the charge itself is the thing to compare gravity with.

But now I wonder something: Does a moving gravitational object create anything that could be compared to the magnetic field created by a moving electric charge?

Yes, it is predicted to do so in GR, it is known generally as gravitomagnetism. More specifically, it is what is responsible for frame dragging. It is, however a very weak effect.

I'm wondering: Does anything prevent a black hole from emitting energy via gravito-magnetism?

I'm thinking that, if the black hole moves at all, then presumably its gravitational field is creating gravito-magnetic fields as well, and a changing gravito-magnetic field would be a means of transferring energy. (At least if gravito-magnetism and ordinary magnetism are similar in this regard)

Does anything stop that from working?

What I'm wondering is whether this provides a mechanism for energy to escape the black hole.

Well yes. A very special type of curvature would need to be introduced so that radiation cannot escape. But this will only work on scales, like electrons. However, to clear something up, its the rotation of a black hole which produces any magnetism, not it rather moving through spacetime, because this is wrong - instead, spacetime is dragged with a black hole, like a drain sucks down water. So we have a spinning drain. Weird eh?