View Full Version : Black holes and angular momentum

2013-Dec-05, 12:36 PM
Do black holes transfer angular momentum back out beyond the accretion disk?

I can find reference to frame dragging and gravitational waves, but for an active black hole these seem very weak compared to the AM coming in from outside.:confused:

2013-Dec-05, 12:48 PM
Well I did write a paper once about magnetic connections between the horizon of a black hole and the accretion disk.
That is one way of transporting angular momentum, due to the shearing of the magnetic field, but the connection flares rather quickly.
Here you can download the paper (http://esoads.eso.org/abs/1993A%26A...270..265V).

2013-Dec-05, 04:02 PM
Sorry, I got totally lost in the maths of your paper, as it is well beyond me.

Do your flares emit light in a preferred direction?
I was trying to find a paper that estimated the amount of angular momentum an accretion disk could lose via synchrotron radiation.
The total momentum of all the x-rays emitted by an active black hole is enormous.
If they were sent out in the direction of rotation at a reasonable offset from the axis of rotation, I think they could be a large contributor to balancing the AM budget in the disk.

2013-Dec-06, 02:44 PM
Yes, I guess it can get messy with math, it is also not really about momentum transfer, but it is related to it, because of the shearing magnetic field.
The flares do not emit in a special direction, it is just random.
A friend/colleague of mine applied something similar to AGNs to obtain the variable X-ray emission (here (http://esoads.eso.org/abs/1992A%26A...266...77D)).
I fail, however, to see how these X-rays can "balance the AM budget", mainly because I do not understand what you mean with "AM budget" (assuming AM = accretion mass?).

2013-Dec-06, 03:47 PM
Anti matter? Angular momentum? Actual motion? Aggressive monobrow?

2013-Dec-06, 03:48 PM
Anti matter? Angular momentum? Actual motion? Aggressive monobrow?

:doh: I just read the thread title. :doh:

2013-Dec-06, 04:08 PM
Sorry, that was a bit unclear.

I was referring to an angular momentum(AM) budget, ie. balancing angular momentum being transferred into the accretion disk by material falling in, against that being transferred outwards into space.
There are several interesting papers showing how angular momentum is transferred outwards into the disk, but I can't find many papers on how it is transferred out beyond the disk.
If AM keeps accumilating in the disk faster than the black hole gains mass to keep hold of it, something has to give.

After your first reply, I was trying to figure out how much angular momentum could be carried out into deep space by synchrotron radiation.
If it was possible that the black hole's magnetic field was frozen at the even horizon, then particles orbiting at relativistic speeds would dump their AM out into space as X-rays, as they spiral in.