Galaxies without dark matter halos?

"g" == greywolf42 writes:

g Steve Willner wrote in message
g ...

Supergiants are not late-type (i.e. cool, main sequence) stars.
A red supergiant is the remnant of an O or B star.

Supergiants come in both early and late types. "Late-type" is a
synonym for "cool." It does not imply main sequence. Your second
sentence above is corrrect.

g "Late-type" is not simply a synonym for 'cool.' Do you have a
g reference for your view?

From Pasachoff, _Contemporary Astronomy_ (1989, p. 83) (this is a
standard textbook for introductory non-major astronomy courses)

Historically, the hotter stars are called early types and the
cooler stars are called late types.

Can you provide a (fairly standard) reference for your view that
late-type applies to the star's evolutionary state?

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

g Joseph Lazio wrote in message
g ...

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.

g I gave you the standard text by Tayler, and excerpts from same.

I finally had the chance to look at Tayler. I'll confess, I don't
understand why you reference it.

The reasons are given in the posts where I reference Tayler:

From 10/7: "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."

From 9/13: "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. "

In short, I mention Tayler because the book identifies a local mechanism --
pressure equalization between gas regions -- that causes gas regions to move
together. Regardless of which region is doing the 'driving.'


In Chapter 2 he discusses rotation velocities of stars and gas within
the Galaxy. He cites a couple of different estimates of stellar
rotational velocities, which are between 200 and 300 km/s. He also
provides rotation curves derived from gas motions, which are in the
range 220--240 km/s. No major discrepancy here, as Steve Willner has
already pointed out.

Perhaps you could look a little more closely at those estimates of stellar
rotation. You'll see they are all based on measuring gas or O and B stars
(recently condensed from same). As I have repeatedly pointed out. If you
know of any study different, please identify it.

* 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.

g What type of secondary 'observational' evidence would you accept,
g since we can't directly observe such without an interstellar probe?

Why can't you just provide what you think to be the evidence?

Because the moderator literally will not allow mention of that subject or
references for same in this newsgroup. I originally provided the reference
(The Big Bang Never Happened, by Lerner, p230 et seq). The moderator
explicitly informed me* that no mention of that book would be allowed in the
newsgroup, because it was "well known" that the book was "riddled with
errors." When I then provided Peratt's peer-reviewed simulation papers on
the same subject (Astrophysics and Space Science, 1983), the moderator
informed me that those simulations would not be allowed to be mentioned,
because they were "too old". The moderator refused to accept any reference
on the subject dated prior to 2000 (and "Sky and Telescope" was not to be
allowed at all, as being an inferior publication).

*When I asked for a reference to the flaws in the book, the moderator
pointed me to Ned Wright's site. However, the moderator also would allow no
critique whatsoever of Ned Wright's site to appear in this newsgroup -- even
though that site is the only reference the moderator could come up with to
justify 'banning' the book (TBBNH) from the newsgroup. None of those
critiques concerned the plasma-driven rotation of the galaxy.

If interested, see:
http://www.google.com/groups?selm=vk....supernews.com
http://www.google.com/groups?selm=vk....supernews.com
http://www.google.com/groups?selm=vk....supernews.com
http://www.google.com/groups?selm=vk....supernews.com
http://www.google.com/groups?selm=vk....supernews.com
http://www.google.com/groups?selm=vk....supernews.com
http://www.google.com/groups?selm=vk....supernews.com
and
http://www.google.com/groups?selm=vk....supernews.com


Moreover, Tayler describes magnetic fields in Chapter 6, citing values
similar to what John Park assumed (length scales ~ 100 pc and field
strengths ~ few microGauss). You've objected to both of these values,

No, I have not. I accepted both.

arguing for much smaller length scales

Again, it is not the *length* of the filament that is the critical
dimension, but the thickness that is important.

and higher field strengths,

I accepted the moderator's field strength.

but I'll have to confess I don't understand why.

I can't understand, either. Perhaps too much time has passed since my
postings, and you should read them again.

* 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.)

g I'm not at all confused. The motion of ionized hydrogen (atoms)
g and the motion of neutral hydrogen (molecules) are both measured.
g Hence, the reference I gave you to Tayler.

This sounds like a "Yes, you do. No, I don't" argument. I can't do
any more than say that, after re-reading your posts on Google, I
continue to think you do not make this distinction. Perhaps if you
were to supply a succinct summary of your idea it would clear up some
confusion.

I've done this repeatedly. See the above quotes from Tayler (again). Also,
see my summary immediately below.

* You continue to rely on pressure equilibrium, even though this is
widely known to be true only on average (...) and there are clear
examples of shock waves in the ISM.

g You asked for evidence that pressure could equalize the rotation
g rates of ionized and non-ionized gas. If -- as discussed in Tayler
g -- "ionized gas clouds and non-ionized gas clouds roughly maintain
g equal pressures between region boundaries," then the time scale for
g maintaining these equal pressures must be far less than the time to
g orbit the center of the galaxy. Otherwise, there wouldn't *be*
g different regions.

g Yes, it is the 'average' situation. And the average situation is
g what we look at when we measure overall galactic rotation curves.

The "average" that Tayler forms is over kiloparsec scales.

Gas regions are not limited to kiloparsec dimensions. Tayler does not limit
this average to kiloparsec regions.

Yes the average *motions* of the individual gas regions are conglomerated
over kiloparsec regions. But the gas regions are in rough pressure
equilibrium with each other. Therefore they move together.

You seem
to assert that pressure equilibrium continues to hold even on
sub-parsec scales.

Nope.

That's a huge extrapolation, and one for which we
have some evidence to the contrary.

Then perhaps you shouldn't have made such an extrapolation. Please try
dealing with my arguments as I wrote them, and avoid anything that begins
"you seem to assert." That's a dead giveaway that this isn't my argument.

Admittedly, I was browsing through Tayler's text after midnight last
night. I could have missed something. Perhaps you might provide a
succinct summary of your idea (and the evidence supporting it?) to
clear up the confusion?

Already done. Several times.

Perhaps you could actually think about the physical dynamics of the
situation. Instead of attempting to find a word-for-word authority for my
position.

--
greywolf42
ubi dubium ibi libertas
{remove planet for return e-mail}

"g" == greywolf42 writes:

g Joseph Lazio wrote in message
g ...

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.

g I gave you the standard text by Tayler, and excerpts from same.

I finally had the chance to look at Tayler. I'll confess, I don't
understand why you reference it.

g The reasons are given in the posts where I reference Tayler:
g [invocations of pressure equilibrium]
g In short, I mention Tayler because the book identifies a local
g mechanism -- pressure equalization between gas regions -- that
g causes gas regions to move together. Regardless of which region is
g doing the 'driving.'

As I've pointed out, and as Tayler discusses in Chap. 6, pressure
equilibrium only applies on global scales, length scales much larger
than those relevant for the interfaces between neutral and ionized
regions.

In Chapter 2 he discusses rotation velocities of stars and gas
within the Galaxy. He cites a couple of different estimates of
stellar rotational velocities, which are between 200 and 300 km/s.
He also provides rotation curves derived from gas motions, which
are in the range 220--240 km/s. No major discrepancy here, as
Steve Willner has already pointed out.

g Perhaps you could look a little more closely at those estimates of
g stellar rotation. You'll see they are all based on measuring gas
g or O and B stars (recently condensed from same). As I have
g repeatedly pointed out.

I have looked closely at Tayler's discussion. I see no explicit
mention of stellar types, but the methods he describes seem to rely on
late-type stars (so A, F, G, etc.). One method he describes is
measuring the velocity of the Local Standard of Rest, which is defined
by stars in the solar neighborhood (so mostly late-type stars),
relative to globular clusters (which again are late-type stars).
Later in the chapter he describes measuring the Oort A and B constants
"from nearby stars," which are mostly late-type stars, and obtaining a
rotational velocity of 220 km/s.

* 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.

g What type of secondary 'observational' evidence would you accept,
g since we can't directly observe such without an interstellar probe?

Why can't you just provide what you think to be the evidence?

g Because the moderator literally will not allow mention of that
g subject or references for same in this newsgroup. [Long rant on
g sci.astro.research moderator, but no mention of evidence....]

g If interested, see: [...]

I just don't see how many of these are relevant. The only mention of
plasma filaments comes in a discussion of jets from galaxy cores. I
don't see how that relates to the motion of gas in our Galaxy, and in
any event the length scales are parsecs, much larger than what you'd like.

Moreover, Tayler describes magnetic fields in Chapter 6, citing
values similar to what John Park assumed (length scales ~ 100 pc
and field strengths ~ few microGauss). You've objected to both of
these values,
[...]
g Again, it is not the *length* of the filament that is the critical
g dimension, but the thickness that is important.

Where does Tayler discuss filaments at all?




Admittedly, I was browsing through Tayler's text after midnight
last night. I could have missed something. Perhaps you might
provide a succinct summary of your idea (and the evidence
supporting it?) to clear up the confusion?

g Already done. Several times.

g Perhaps you could actually think about the physical dynamics of the
g situation. Instead of attempting to find a word-for-word authority
g for my position.

I'm getting the increasing sense that this is pointless. I think I
have made a good faith effort to read what you've written and read
what you reference.

--
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:
"g" == greywolf42 writes:


g Joseph Lazio wrote in message
g ...


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.


g I gave you the standard text by Tayler, and excerpts from same.


I finally had the chance to look at Tayler. I'll confess, I don't
understand why you reference it.


g The reasons are given in the posts where I reference Tayler:
g [invocations of pressure equilibrium]
g In short, I mention Tayler because the book identifies a local
g mechanism -- pressure equalization between gas regions -- that
g causes gas regions to move together. Regardless of which region is
g doing the 'driving.'

As I've pointed out, and as Tayler discusses in Chap. 6, pressure
equilibrium only applies on global scales, length scales much larger
than those relevant for the interfaces between neutral and ionized
regions.


In Chapter 2 he discusses rotation velocities of stars and gas
within the Galaxy. He cites a couple of different estimates of
stellar rotational velocities, which are between 200 and 300 km/s.
He also provides rotation curves derived from gas motions, which
are in the range 220--240 km/s. No major discrepancy here, as
Steve Willner has already pointed out.


g Perhaps you could look a little more closely at those estimates of
g stellar rotation. You'll see they are all based on measuring gas
g or O and B stars (recently condensed from same). As I have
g repeatedly pointed out.

I have looked closely at Tayler's discussion. I see no explicit
mention of stellar types, but the methods he describes seem to rely on
late-type stars (so A, F, G, etc.). One method he describes is
measuring the velocity of the Local Standard of Rest, which is defined
by stars in the solar neighborhood (so mostly late-type stars),
relative to globular clusters (which again are late-type stars).
Later in the chapter he describes measuring the Oort A and B constants
"from nearby stars," which are mostly late-type stars, and obtaining a
rotational velocity of 220 km/s.


* 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.


g What type of secondary 'observational' evidence would you accept,
g since we can't directly observe such without an interstellar probe?


Why can't you just provide what you think to be the evidence?


g Because the moderator literally will not allow mention of that
g subject or references for same in this newsgroup. [Long rant on
g sci.astro.research moderator, but no mention of evidence....]

g If interested, see: [...]

I just don't see how many of these are relevant. The only mention of
plasma filaments comes in a discussion of jets from galaxy cores. I
don't see how that relates to the motion of gas in our Galaxy, and in
any event the length scales are parsecs, much larger than what you'd like.

Hi guys, I just have to jump in he
you have 'energy' (gazillions of stars plus gas, whatever)
rotating as a disc around a center.
Surprise, surprise, you have a humungous magnetic field
projecting at right angles to that center.
Now, why would that field not be relevant to that rotation?
(think 'electromagnet')

Once someone shows that these discs are precessing, and
the plasma that was shot out is being continually swept back up and
made back into stars, you have the whole cycle.
:-)
John
http://rapfast.petcom.com/~john/

"JS" == John Sefton writes:

JS I just have to jump in he you have 'energy' (gazillions of
JS stars plus gas, whatever) rotating as a disc around a center.
JS Surprise, surprise, you have a humungous magnetic field projecting
JS at right angles to that center. Now, why would that field not be
JS relevant to that rotation? (think 'electromagnet')

Two reasons: First, the energy contained in the magnetic field is
much less than the energy contained in the rotation. The interstellar
magnetic field has a strength of roughly 3 microGauss, implying a
magnetic energy density of order 4E-13 erg/cm^3. The kinetic energy
density of the stars (just the stars) in the solar neighborhood is
roughly 1000 times larger. How can such a weak field impart so much
energy?

Second, what's rotating, the stars and gas, are neutral. One has to
figure out how to couple the magnetic field to the neutral stars and
gas.

--
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