How can black holes "expell" jets of gas?

I will admit to being a little confused after reading the alt.astronomy
FAQ, and note that Google groups simply lists sci.astronomy as "an
archive" to which I can not pose questions. I have what I think is a
simple question.

In the July 2006 issue of Sky & Telescope, there's an article about how
many galaxies are at one (or more) point(s) in their careers quasars.
This is because they have large black holes at their centers, which
accrete large volumes of gas, stars, and even other galaxies. However,
in this process, they are described as expelling "jets" of gas, some of
which are accelerated close to "the speed of light."

My understanding of black holes is that of a lay person, rather than
mathematical. This seems to contradict the notion of a black hole. One
quote from the article is that as gas approaches the black hole, it
releases energy, which is flung away from the black hole. I'm not sure
how this is possible. After gas (or indeed matter in general) has begun
its "fall" into the black hole, I thought it was inevitable that it
would wind up there?

If I've posted here in error, I apologize.

Alex

wrote in message ups.com...
I will admit to being a little confused after reading the alt.astronomy
FAQ, and note that Google groups simply lists sci.astronomy as "an
archive" to which I can not pose questions. I have what I think is a
simple question.

In the July 2006 issue of Sky & Telescope, there's an article about how
many galaxies are at one (or more) point(s) in their careers quasars.
This is because they have large black holes at their centers, which
accrete large volumes of gas, stars, and even other galaxies. However,
in this process, they are described as expelling "jets" of gas, some of
which are accelerated close to "the speed of light."

My understanding of black holes is that of a lay person, rather than
mathematical. This seems to contradict the notion of a black hole. One
quote from the article is that as gas approaches the black hole, it
releases energy, which is flung away from the black hole. I'm not sure
how this is possible. After gas (or indeed matter in general) has begun
its "fall" into the black hole, I thought it was inevitable that it
would wind up there?

If I've posted here in error, I apologize.

The material comprising the jets was never below
the event horizon of the black hole, it is material
that is forced away from the accretion disk and
"squirted out" along the polar axes. There's
probably some very nifty magnetohydrodynamical
processes involved in entraining the material to
migrate from the equator to the poles and
collimating it into jets.

In article . com,
" wrote:

The material comprising the jets was never below
the event horizon of the black hole, it is material
that is forced away from the accretion disk and
"squirted out" along the polar axes. There's
probably some very nifty magnetohydrodynamical
processes involved in entraining the material to
migrate from the equator to the poles and
collimating it into jets.

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

The magnetic field is that strong. The jets are a similar effect to
that seen from a pulsar.

--
The greatest enemy of science is pseudoscience.

Jaffa cakes. Sweet delicious orangey jaffa goodness, and an abject lesson why
parroting information from the web will not teach you cosmology.

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

wrote:
I will admit to being a little confused after reading the alt.astronomy
FAQ,


The alt.astronomy FAQ is a FAKE.

Double-A

Avriette A black hole is not really part of the universe,but the
accretion disk it creates is. The accretion disk is made from a star
that got to close to a black hole,and most of its material is spiralling
in. The force of angular motion ,and the black holes force of gravity at
a distance creates this disk of moving particles,and energy. Some of
this disk is radiated out into space,but most of it reaches the event
horizon close to the speed of light. Once hitting the black holes
surface it is lost from the universe,and adds to the mass density of the
black hole. My image of the disk has it looking like a question mark ?
and the dot on the bottom is the black hole. Lots can be learned from
this accretion shaped question mark;. Reality is its like
looking at the big bang in reverse. Gravity created the stars,and
gravity is showing us it can remove what it has created Bert

wrote in message oups.com...

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?

Temperatures in the accretion disk are *very* high. The matter
there is ripped apart into a plasma composed of electrons,
protons, and some very highly ionized nuclei. These charged
particles are subject to interaction with the powerful
electromagnetic fields wrapped around the black hole.

On 12 Jun 2006 03:25:05 -0700, "Double-A" wrote:


wrote:
I will admit to being a little confused after reading the alt.astronomy
FAQ,


The alt.astronomy FAQ is a FAKE.

It should have Qs such as:
Is there only one Uranus?

CeeBee ceebee@novalidmail wrote in
2.164:

" 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.

A nice introduction to black holes:

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


I recall reading somewhere that black holes act as extremely efficient
"power stations" in this process. The kinetic energy of the emitted jets is
a high proportion of the gravitational potential energy of the infalling
material. Having now solved the energy crisis we will now hand this over to
the engineering department to sort out the practical details ;-).

Klazmon.

I thought the FAQ was dead on! Has it changed lately?

Saul Levy


On 12 Jun 2006 03:25:05 -0700, "Double-A" wrote:


wrote:
I will admit to being a little confused after reading the alt.astronomy
FAQ,


The alt.astronomy FAQ is a FAKE.

Double-A