Black hole acreting binary -magnetic fields

[skydivephil]

In a white dwarf acreting binary we would make distinction between thsoe with weak magnetic field that make an acretion disc and those with strong magentic fields where the material from the larger star gets funneled along the field lines.
But in a black hole binary all of the energy is released at the acretiion disc. But what does that mean for the magentic field of the balck hole. Does it have a magentic field? If so how does that affect the way the matieral would be chanelled?

 

[Chronos]

A good question! A Kerr black hole [the most likely species] should have a strong magnetic field and powerful jets, but, our technology is still a little too primitive to yield convincing data.

 

[skydivephil]

Thanks Chronos, but is there a theory that's accepted? Normally when there is a strong magentic field the larger stars material can't cross the field lines and so does not form an acretion disc. Instead it gets tangled on the field lines and goes straight to the comapct star.
But the black hole must radiate its energy at the acretion disc as it has no solid surface so I see a problem here, is there any consensus resolution?

 

[Chronos]

Well, we still have a hard time making the case for the existence of black holes, much less properties of their accretion discs. If its any consolation, we have strong evidence for the existence of condensed matter objects [e.g., neutron stars] with powerful magnetic fields.

 

[twofish-quant]

But the black hole must radiate its energy at the acretion disc as it has no solid surface so I see a problem here, is there any consensus resolution?

Yes.

There is something called the Membrane paradigm. Essentially even though the black hole doesn't really have a solid surface, the fact that from the point of a distant observer, it *appears* that matter is freezing just before it enters the black hole, gives you something that acts like a solid surface that you can attach a magnetic field to.

http://en.wikipedia.org/wiki/Membrane_paradigm

The "apparent surface" of a black hole still acts quite differently from a real surface. The big difference is that when you drop a lot of matter onto a neutron star, it hits the surface and creates a massive burst of energy. The "apparent surface" of a black hole let's the matter fall through, and from a distant observer it appears to freeze, which means that you won't get any bursts.

 

[skydivephil]

Im thinking more of what happens to the material before it falls down the black hole. In white dwarf binaries for example it doesn't have to form an acretion disc. if there are strong magentici fields then the material infact wotn form an acretion disc but will travel along the field lines to the white dwarf.
So it seems the same would happen to a black hole if it has strong magentic fields. The problem is , hwo can the material lose angualr momentum if not at the acretion disc?