CeeBee wrote:
" wrote in alt.astronomy:


What causes it to be forced away from the accretion disk, whereas the
rest of the matter is "sucked" towards it?

Outside the event horzion there are stable orbits possible, with matter
neither sucked in nor repelled away. Think of the Earth's orbit around the
Sun. Come too close, you end up sucked in, get too far too fast and you'll
never see the Sun again. Right speed and distance, and you'll have a stable
orbit.

It's not quite understood, but due to the fast rotation of the black hole
magnetic fields emerge, enabling matter in the accretion disk, outside the
event horzion, spinning around the black hole to be jettisoned away.

In this model the magnetic fields are intertwined and create channels that
might conduct the jets.

This is all very helpful, thank you folks.

As I read this, I think, wouldn't that create a disk of retreating
material as well as a disk of "falling in" material? What comes to mind
specifically is refraction. Refraction isn't something governing the
movement of matter, but the equality of the angle of incidence and the
angle of refraction seems to describe "the angle of approach" and "the
angle of exit" in the example posed here, with gravity. Because all
material is coming to the "hole" from a disk, that material which
escaped would be escaping from all angles, rather than just one
particular angle (as it all arrived from different angles). This is
further weird (to me) because these "jets" seem to be expelling at
angles which are perpendicular (on the Z axis) to the accretion disk.

The fact that the black hole is spinning seems to me to further cement
the notion that it couldn't all be ejected from one (or two) places.

What's further confused me about the above two answers is the mention
of the magnetic field. Does this mean that as matter approaches the
event horizon, some of it becomes polarized opposite to the black hole?
How could that be possible, if the hole itself is spinning?

A nice introduction to black holes:

http://hubblesite.org/discoveries/black_holes/

Stop me if I've wandered off into the weeds and need to examine some
elementary physics.

Alex