Galaxies without dark matter halos?

John Park wrote in message
...
greywolf42 ) writes:
John Park wrote in message
...
greywolf42 ) writes:
John Park wrote in message
...

But why should a mu.grad(B) force have the same direction as a vxB
force?

Because the magnetic fields themselves are moving through space.
Hence,
one
gets a 'dragging along' from both B field and grad B field.

How do you know they're both "dragging" forces?

Because the plasma filaments are structures that contain roughly
cylindrical
fields. As each filament moves by the gas, it will impart a net
acceleration to the gas.

Acceleration, maybe. Maybe. But why "drag", rather than repulsion, say?

'Drag' was more descriptive. Use repulsion if it helps the visualization.
After the flimament has passed, the gases have been accelerated to follow
the filament.

[...]

You should have used hydrogen GAS. Which is normally a molecule:
H2. And has a larger moment.

No, I was being generous: H2 is diamagnetic; H is paramagnetic.

Makes no difference.

Care to quote the relevant magnetic moments?

The net effect of the moving filaments is independent of whether the
atom/molecule is paramagnetic or diamagnetic. What has this to do with your
argument?

{AH! The classic 'invisible' snip!}
=========================

{and the 'invisible' snip within the 'invisible' snip -- which I'll ignore
for now}

But, if you don't like the potential for magnetic gradient's there's the
standard interpretation that ionized gas clouds and non-ionized gas
clouds
roughly maintain equal pressures between region boundaries. ("Galaxies:
Structure and Evolution", R.J. Tayler) Hence, once you 'drive' the
ionized
clouds, you will literally drag the non-ionized clouds around.
=========================

Quite simply, John deleted that with which he couldn't argue.

Quite simply, I was addressing the basic physics question of whether a
magnetic field would accelerate neutral and ionised gases in the same way.
How this fits into your other arguments is a separate issue, and one I
have no strong views on, at the moment.

The basic physics question under discussion is whether neutral gas will be
accelerated in a disk galaxy undergoing electromagnetically-driven rotation
of ionized gas. Since there were repeated objections to magnetic gradients
affecting the magnetic moments of neutral gas, I provided a second physical
force that might be more palatable.

The issue is not about fundamental EM fields -- but how the motions of
intragalactic gas (observed to be decoupled from stellar motions, but
neutral and ionized gas is coupled) can be explained.

greywolf42
ubi dubium ibi libertas

"g" == greywolf42 writes:

g John Park wrote in message
g ...

"Far more" sounds right. If the magnetic field gradient is as high
as 10 microGauss per kiloparsec,

g Where did you come up with this number? The magnetic fields
g certainly don't have to be uniform over thousands of parsecs.
g Plasma filaments (from those ionized gas regions) should have
g typical widths on the order of AU to thousands of AU, not
g kiloparsecs.

Uh, what plasma filaments? I'm aware of the filaments in the Galactic
center, which have typical lengths of 10 pc, but that's it.

g And with an 'accepted' magnetic field strength of 5 micro G, this
g would be tens of thousands to millions of times higher gradient.
g Why don't you at least look at the theories that have been
g proposed, before you head off with trying to disprove them?

I suppose that I will start a flame war if I point out that you have
not been particularly forthcoming with some of these numbers.

I estimate that, acting on the magnetic moment of a (neutral)
hydrogen atom,

g You should have used hydrogen GAS. Which is normally a molecule:
g H2. And has a larger moment.

Why favor molecular hydrogen? I thought that the amount of atomic and
molecular hydrogen in the Galaxy was roughly comparable, and atomic
hydrogen is certainly far more widely distributed. Moreover, rotation
curves are constructed from measurements of atomic hydrogen.

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"g" == greywolf42 writes:

g John Park wrote in message
g ...

"Far more" sounds right. If the magnetic field gradient is as high
as 10 microGauss per kiloparsec,

g Where did you come up with this number? The magnetic fields
g certainly don't have to be uniform over thousands of parsecs.
g Plasma filaments (from those ionized gas regions) should have
g typical widths on the order of AU to thousands of AU, not
g kiloparsecs.

Uh, what plasma filaments? I'm aware of the filaments in the Galactic
center, which have typical lengths of 10 pc, but that's it.

g And with an 'accepted' magnetic field strength of 5 micro G, this
g would be tens of thousands to millions of times higher gradient.
g Why don't you at least look at the theories that have been
g proposed, before you head off with trying to disprove them?

I suppose that I will start a flame war if I point out that you have
not been particularly forthcoming with some of these numbers.

I estimate that, acting on the magnetic moment of a (neutral)
hydrogen atom,

g You should have used hydrogen GAS. Which is normally a molecule:
g H2. And has a larger moment.

Why favor molecular hydrogen? I thought that the amount of atomic and
molecular hydrogen in the Galaxy was roughly comparable, and atomic
hydrogen is certainly far more widely distributed. Moreover, rotation
curves are constructed from measurements of atomic hydrogen.

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Joseph Lazio wrote in message
...
"g" == greywolf42 writes:

g John Park wrote in message
g ...


I presume that you now understand how the motion of filaments will impart a
net "drag" on the gas as it moves through. Since you 'invisibly' snipped
the discussion.


"Far more" sounds right. If the magnetic field gradient is as high
as 10 microGauss per kiloparsec,

g Where did you come up with this number? The magnetic fields
g certainly don't have to be uniform over thousands of parsecs.
g Plasma filaments (from those ionized gas regions) should have
g typical widths on the order of AU to thousands of AU, not
g kiloparsecs.

Uh, what plasma filaments?

The plasma filaments in the theory under discussion.

I'm aware of the filaments in the Galactic
center, which have typical lengths of 10 pc, but that's it.

The dimension of note is the *width* or thickness of the filaments. Not
their length. For the field changes side-to-side as well as along the
length.

g And with an 'accepted' magnetic field strength of 5 micro G, this
g would be tens of thousands to millions of times higher gradient.
g Why don't you at least look at the theories that have been
g proposed, before you head off with trying to disprove them?

I suppose that I will start a flame war if I point out that you have
not been particularly forthcoming with some of these numbers.

To avoid a reference war, I 'accepted' the field strength of 5 micro G
stated by the moderator of the group.

To what other numbers are you referring with "some of these numbers?"

I estimate that, acting on the magnetic moment of a (neutral)
hydrogen atom,

g You should have used hydrogen GAS. Which is normally a molecule:
g H2. And has a larger moment.

Why favor molecular hydrogen?

Because it has a larger magnetic moment than atomic hydrogen.

I thought that the amount of atomic and
molecular hydrogen in the Galaxy was roughly comparable, and atomic
hydrogen is certainly far more widely distributed. Moreover, rotation
curves are constructed from measurements of atomic hydrogen.

What is your point?

And, replacing the final 'invisible' snip:
g But, if you don't like the potential for magnetic gradient's there's
the
g standard interpretation that ionized gas clouds and non-ionized gas
clouds
g roughly maintain equal pressures between region boundaries.
("Galaxies:
g Structure and Evolution", R.J. Tayler) Hence, once you 'drive' the
ionized
g clouds, you will literally drag the non-ionized clouds around.

greywolf42
ubi dubium ibi libertas

Joseph Lazio wrote in message
...
"g" == greywolf42 writes:

g John Park wrote in message
g ...


I presume that you now understand how the motion of filaments will impart a
net "drag" on the gas as it moves through. Since you 'invisibly' snipped
the discussion.


"Far more" sounds right. If the magnetic field gradient is as high
as 10 microGauss per kiloparsec,

g Where did you come up with this number? The magnetic fields
g certainly don't have to be uniform over thousands of parsecs.
g Plasma filaments (from those ionized gas regions) should have
g typical widths on the order of AU to thousands of AU, not
g kiloparsecs.

Uh, what plasma filaments?

The plasma filaments in the theory under discussion.

I'm aware of the filaments in the Galactic
center, which have typical lengths of 10 pc, but that's it.

The dimension of note is the *width* or thickness of the filaments. Not
their length. For the field changes side-to-side as well as along the
length.

g And with an 'accepted' magnetic field strength of 5 micro G, this
g would be tens of thousands to millions of times higher gradient.
g Why don't you at least look at the theories that have been
g proposed, before you head off with trying to disprove them?

I suppose that I will start a flame war if I point out that you have
not been particularly forthcoming with some of these numbers.

To avoid a reference war, I 'accepted' the field strength of 5 micro G
stated by the moderator of the group.

To what other numbers are you referring with "some of these numbers?"

I estimate that, acting on the magnetic moment of a (neutral)
hydrogen atom,

g You should have used hydrogen GAS. Which is normally a molecule:
g H2. And has a larger moment.

Why favor molecular hydrogen?

Because it has a larger magnetic moment than atomic hydrogen.

I thought that the amount of atomic and
molecular hydrogen in the Galaxy was roughly comparable, and atomic
hydrogen is certainly far more widely distributed. Moreover, rotation
curves are constructed from measurements of atomic hydrogen.

What is your point?

And, replacing the final 'invisible' snip:
g But, if you don't like the potential for magnetic gradient's there's
the
g standard interpretation that ionized gas clouds and non-ionized gas
clouds
g roughly maintain equal pressures between region boundaries.
("Galaxies:
g Structure and Evolution", R.J. Tayler) Hence, once you 'drive' the
ionized
g clouds, you will literally drag the non-ionized clouds around.

greywolf42
ubi dubium ibi libertas

"g" == greywolf42 writes:

g Joseph Lazio wrote in message
g ...

g I presume that you now understand how the motion of filaments will
g impart a net "drag" on the gas as it moves through. Since you
g 'invisibly' snipped the discussion.

No, because you've never provided a succint summary of the idea. The
best I've gathered is that you think there are plasma filaments in the
interstellar medium having widths of order 100 AU. The observational
evidence for such filaments is not clear. You suppose that they
induce a dipolar moment in molecular hydrogen of the sufficient size
so as to produce velocities of order 200 km/s. You do not indicate
how the hydrogen molecules in molecular clouds then impart this
velocity to the hydrogen atoms in the more diffuse neutral medium nor
do you indicate how the hydrogen atoms in the outer Galaxy, where
there is little molecular hydrogen, obtain their velocities, which are
also about 200 km/s.

g And, replacing the final 'invisible' snip: But, if you don't like
g the potential for magnetic gradient's there's the standard
g interpretation that ionized gas clouds and non-ionized gas clouds
g roughly maintain equal pressures between region boundaries.
g ("Galaxies: Structure and Evolution", R.J. Tayler) Hence, once you
g 'drive' the ionized clouds, you will literally drag the non-ionized
g clouds around.

O.k., now that's a potentially useful, though still confusing,
starting point. So using typical sizes and velocities of these
ionized clouds and assuming a neutral medium moving at a much slower
velocity, please illustrate typical time scales to obtain the observed
situation, in which gas in the Milky Way rotates at velocities near
200 km/s. Showing your work would be appreciated.

(What confuses me is above you talk about molecular hydrogen and here
you talk about ionized hydrogen. So which is it?)

--
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sci.astro FAQ at http://sciastro.astronomy.net/sci.astro.html

"g" == greywolf42 writes:

g Joseph Lazio wrote in message
g ...

g I presume that you now understand how the motion of filaments will
g impart a net "drag" on the gas as it moves through. Since you
g 'invisibly' snipped the discussion.

No, because you've never provided a succint summary of the idea. The
best I've gathered is that you think there are plasma filaments in the
interstellar medium having widths of order 100 AU. The observational
evidence for such filaments is not clear. You suppose that they
induce a dipolar moment in molecular hydrogen of the sufficient size
so as to produce velocities of order 200 km/s. You do not indicate
how the hydrogen molecules in molecular clouds then impart this
velocity to the hydrogen atoms in the more diffuse neutral medium nor
do you indicate how the hydrogen atoms in the outer Galaxy, where
there is little molecular hydrogen, obtain their velocities, which are
also about 200 km/s.

g And, replacing the final 'invisible' snip: But, if you don't like
g the potential for magnetic gradient's there's the standard
g interpretation that ionized gas clouds and non-ionized gas clouds
g roughly maintain equal pressures between region boundaries.
g ("Galaxies: Structure and Evolution", R.J. Tayler) Hence, once you
g 'drive' the ionized clouds, you will literally drag the non-ionized
g clouds around.

O.k., now that's a potentially useful, though still confusing,
starting point. So using typical sizes and velocities of these
ionized clouds and assuming a neutral medium moving at a much slower
velocity, please illustrate typical time scales to obtain the observed
situation, in which gas in the Milky Way rotates at velocities near
200 km/s. Showing your work would be appreciated.

(What confuses me is above you talk about molecular hydrogen and here
you talk about ionized hydrogen. So which is it?)

--
Lt. Lazio, HTML police | e-mail:
No means no, stop rape. | http://patriot.net/%7Ejlazio/
sci.astro FAQ at http://sciastro.astronomy.net/sci.astro.html

Joseph Lazio wrote in message
...
No, because you've never provided a succint summary of the idea.

First you claim that there's not enough detail. Now you complain that I
haven't provided a sufficiently succinct summary. All the while performing
'invisible' snips of the arguments.

The
best I've gathered is that you think there are plasma filaments in the
interstellar medium having widths of order 100 AU. The observational
evidence for such filaments is not clear. You suppose that they
induce a dipolar moment in molecular hydrogen of the sufficient size
so as to produce velocities of order 200 km/s. You do not indicate
how the hydrogen molecules in molecular clouds then impart this
velocity to the hydrogen atoms in the more diffuse neutral medium nor
do you indicate how the hydrogen atoms in the outer Galaxy, where
there is little molecular hydrogen, obtain their velocities, which are
also about 200 km/s.

The 'diffuse neutral medium' is affected the same as the 'clouds.' The only
difference between the two is density. There is no need for the 'clouds' to
impart momentum directly to the 'diffuse medium.'

O.k., now that's a potentially useful, though still confusing,
starting point. So using typical sizes and velocities of these
ionized clouds and assuming a neutral medium moving at a much slower
velocity, please illustrate typical time scales to obtain the observed
situation, in which gas in the Milky Way rotates at velocities near
200 km/s. Showing your work would be appreciated.

I could go look up numbers, but it this really necessary? If -- as
discussed in Tayler -- "ionized gas clouds and non-ionized gas clouds
roughly maintain equal pressures between region boundaries," then the time
scale for maintaining these equal pressures must be far less than the time
to orbit the center of the galaxy. Otherwise, there wouldn't *be* different
regions.

(What confuses me is above you talk about molecular hydrogen and here
you talk about ionized hydrogen. So which is it?)

Perhaps if you did less 'invisible' snipping, the discussion would be easier
to follow.

Your original argument was that EM forces could not affect neutral hydrogen
significantly -- directly or indirectly. I provided you with two physical
mechanisms that can equalize the motion of neutral hydrogen with EM-driven
motion of ionized hydrogen (which you apparently don't have a problem with).

greywolf42
ubi dubium ibi libertas

[Mod. note: quoted text trimmed. If your news client doesn't allow you
to view articles earlier in the thread, get one that does, or use
Google. -- mjh]

Joseph Lazio wrote in message
...
No, because you've never provided a succint summary of the idea.

First you claim that there's not enough detail. Now you complain that I
haven't provided a sufficiently succinct summary. All the while performing
'invisible' snips of the arguments.

The
best I've gathered is that you think there are plasma filaments in the
interstellar medium having widths of order 100 AU. The observational
evidence for such filaments is not clear. You suppose that they
induce a dipolar moment in molecular hydrogen of the sufficient size
so as to produce velocities of order 200 km/s. You do not indicate
how the hydrogen molecules in molecular clouds then impart this
velocity to the hydrogen atoms in the more diffuse neutral medium nor
do you indicate how the hydrogen atoms in the outer Galaxy, where
there is little molecular hydrogen, obtain their velocities, which are
also about 200 km/s.

The 'diffuse neutral medium' is affected the same as the 'clouds.' The only
difference between the two is density. There is no need for the 'clouds' to
impart momentum directly to the 'diffuse medium.'

O.k., now that's a potentially useful, though still confusing,
starting point. So using typical sizes and velocities of these
ionized clouds and assuming a neutral medium moving at a much slower
velocity, please illustrate typical time scales to obtain the observed
situation, in which gas in the Milky Way rotates at velocities near
200 km/s. Showing your work would be appreciated.

I could go look up numbers, but it this really necessary? If -- as
discussed in Tayler -- "ionized gas clouds and non-ionized gas clouds
roughly maintain equal pressures between region boundaries," then the time
scale for maintaining these equal pressures must be far less than the time
to orbit the center of the galaxy. Otherwise, there wouldn't *be* different
regions.

(What confuses me is above you talk about molecular hydrogen and here
you talk about ionized hydrogen. So which is it?)

Perhaps if you did less 'invisible' snipping, the discussion would be easier
to follow.

Your original argument was that EM forces could not affect neutral hydrogen
significantly -- directly or indirectly. I provided you with two physical
mechanisms that can equalize the motion of neutral hydrogen with EM-driven
motion of ionized hydrogen (which you apparently don't have a problem with).

greywolf42
ubi dubium ibi libertas

[Mod. note: quoted text trimmed. If your news client doesn't allow you
to view articles earlier in the thread, get one that does, or use
Google. -- mjh]

"g" == greywolf42 writes:

g Your original argument was that EM forces could not affect neutral
g hydrogen significantly -- directly or indirectly. I provided you
g with two physical mechanisms that can equalize the motion of
g neutral hydrogen with EM-driven motion of ionized hydrogen (which
g you apparently don't have a problem with).

Yes, you have "provided [...] two physical mechanisms that can
equalize the motion of neutral hydrogen with EM-driven motion of
ionized hydrogen." You have not shown that these physical mechanisms
operate or are important in the interstellar medium.

* You've asserted that there are plasma filaments with "typical widths
on the order of AU to thousands of AU," but you've provided no
observational evidence for them.

* You continue to confuse hydrogen atoms (from which rotation curves
are measured commonly) with hydrogen molecules. (See the response
to John Park on 2003-08-30, as well as various postings by me.)

* You continue to rely on pressure equilibrium, even though this is
widely known to be true only on average (for a striking
demonstration of the existence of pressure non-equilibrium in the
interstellar medium, see the massive work by Jenkins & Tripp in the
ApJS) and there are clear examples of shock waves in the ISM.

--
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