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

g Joseph Lazio wrote in message
g ...

TS It has never been the case that all galaxies show evidence for
TS dark matter halos (...).

While true, I think it is still the case that the number of
galaxies requiring dark matter to explain their rotation curves
vastly outnumbers those that do not.

g The fact of existence of a significant number of galaxies without
g dark matter halos (...) would add another layer of 'ad hoc' to the
g dark matter 'ad hoc' postulate.

It would be nice to have some numbers associated with this. One
might expect a few "exceptions to prove the rule."

g ?? Exceptions *never* prove the rule. Especially in science, one
g exception disproves the rule.

g The point is simple. You can't have a valid scientific theory that
g allows you to arbitrarily add and remove 'dark matter' from
g galaxies as needed -- just to match observation and 'save' a
g theory. Such an approach is not disprovable.

You seem to misunderstand dark matter.

The classic special plead fallacy.

The expectation that dark
matter exists is not on par with various theories, such as special
relativity or electromagnetism.

I agree that the existence of dark matter is pure ad hoc speculation.

The velocities of various components of many galaxies cannot be
reproduced with our best theory of gravity if we assume that the
luminous matter represents all of the matter.

The fallacy of the excluded middle, with only one option! The whole point
of the thread is that your *assumption* that interstellar gas moves solely
from gravitational force -- and that stars and gas move in lockstep -- is
not supported by observation.

Thus, we have two
choices: Either general relativity is wrong or we're not seeing
some of the matter. (I suppose one might say three choices, both
are wrong.) General relativity has been well tested, so we're
reluctant to dump it. It's easy to think that we have missed some
matter, particularly because we know of many objects that would be too
faint to be seen at the distances of other galaxies. Thus, the more
simple explanation is that dark matter exists.

If you start with the assumption that gas always moves likes stars, and both
are driven solely by gravity, you *do* come face-to-face with the fact that
galaxies don't match your theory. However, making an ad hoc speculation
that an 'invisible' something exists is pretty lame.

However, galaxies are complicated things. Their formation probably
involves dissipation and turbulence. Moreover, they can be affected
by interactions with other galaxies. Should we expect all galaxies to
be nearly identical? No. Should they all contain the same amount or
same proportion of dark matter? No. Hence, a few exceptions
(galaxies without dark matter) may prove a rule (most galaxies have
dark matter and galaxies are complicated things). This is kind of
equivalent to trying to predict the number of planets in a solar
system. It should be simple, right? It's just gravity and
electromagnetism, both well understood forces. Yet the actual number
of planets is determined by so many aspects of planetary formation
that an actual a priori prediction is well-nigh impossible.

What this demonstrates is your inability to even momentarily consider that
your starting assumption is wrong. The several papers here clearly identify
three things:

1) We measure gas motions, NOT star motions -- except in rare cases.
2) In those rare cases, we measure O and B stars -- that have just recently
condensed from gas.
3) Gas and stars are observed to move differently. The later the stellar
type, the more different from gas motion.

For #1, astronomers have made your pet assumption. For the other two, your
pet assumption is contradicted by observation.

{Replacing a claim made by Mr. Lazio, and a request for backup that he
wanted to avoid.}
=====================================
JL:
I'm not aware that a
"significant" number of galaxies do not require a dark halo to explain
their rotation curve. References?

greywolf42:
Vega-Beltran is the most recent. However, your claim is ".. the number of
galaxies requiring dark matter to explain their rotation curves vastly
outnumbers those that do not." What would you 'a priori' consider a
'significant' number of galaxies?
=====================================
Mr. Lazio is not willing to commit himself to what he considers a
'significant' number of galaxies. This would too easily show his claim
disproved. Hence, he deleted his spurious claim.


You may also wish to review the discussion between Thomas Smid and
myself. Smid pointed to the work of Vega-Beltran. I then
commented that much of Vega-Beltran's work concerns comparisons
between stellar and *ionized* gas motions. He shows reasonable
agreement between the two, at least in the outer portions of
galaxies, where a dark halo requirement is most stringent.

g I disagree with your characterization of your discussion with Smid.
g It's true that you made several similar assertions. But those
g assertions were not backed up by Smid -- or by the work of
g Vega-Beltran.

Umm, care to be more specific? I commented on several papers by
Vega-Beltran.

Sure. You made a vague assertion about your discussion with Smid -- to
which I replied. Because you were vague, I couldn't be more specific.
Let's start with one of Smid's statements:

TS: "(T)he observed anomalous rotation curves of galaxies are practically
always based on gas velocities which can be very different from the
velocities of stars..."

Your response was dismissal of the claim (which is true in all references in
this discussion) and pure assertion to the contrary (sans evidence):

JL: "It would be interesting to see some evidence to back this up. In the
outer reaches of galaxies, rotation curves are based on gas velocities
because there are no (or so few) stars from which to obtain stellar
velocities. However, I think it is the case that within the optical disk,
gas and stellar velocities match fairly well."

Smid was kind enough to provide specific references showing your assertion
was incorrect according to observation:

TS: "I quote from Battaner and Florido ({link}): 'important deviations from
corotation are found in about 14 out of 22
galaxies in the Vega-Beltran sample, where gas and star rotation curves were
measured independently.'"

Your response was to ignore the above statement completely. You diverted
into an earlier statement by Battaner and Florido:

JL: "The stellar disk and the gas in the disk usually corotate, but due to
frequent mergers and the accretion of clouds, captures, etc, this is not
always the case."

Which -- of course -- doesn't change the conclusions of the the B&F paper
one i-dot. Then you dived into a digression with :

JL: "Moreover, I looked up some of Vega-Beltran's papers. (The reference
cited by Battaner & Florido is the Ph.D. thesis, which is often difficult to
find online."

In short, you diverted to completely different papers than were given in
reference by B&F (and Smid)! Yet even these papers do not support your
assertions.

JL: (quoting V-B): "'In the outer regions of all of the sample of 20
galaxies the stellar rotation is comparable to
that of the ionized gas [...], while in the inner regions the following
kinematic features are noteworthy.'"

Q.E.D. Gas and stars do not generally rotate at the same speed.

Unless you can point out where I've misread his papers,
I'm going to have to chalk this up to continuing to try to prove by
assertion.

{snicker}

Moreover, one would think that ionized gas would be more likely to
be affected by magnetic fields than neutral gas.

g Neutral gas is affected by magnetic fields in the same manner as
g ionized gas. It just accelerates more slowly. [...]

More proof by assertion?

LOL! Have you ever taken a physics course? Oh -- no -- I see your slimy
innuendo is deliberte. Because you deleted the explanation of my statement.

Let's put the rest of my statement back in...
"Gas may be paramagnetic or diamagnetic. Gas has a magnetic moment. The
neutral gas will not accelerate as fast as ionized gas will -- but it will
reach the same final velocities relative to the magnetic field."

Your action was both pathetic and dishonest.

Ionized gas should respond strongly to
magnetic fields. If ionized gas and stars have the same velocities,

They don't pea-brain! That's what the references say. No matter how much
you try to ignore them.

why would neutral gas behave differently than ionized gas?

My point was that neutral gas behaves in a manner similar to ionized gas.
It just responds more slowly. But reaches the same final velocities.

There's also the issue I've raised a couple of times in this newsgroup
that the energy contained in the magnetic field does not seem to be
sufficient to explain the velocities.

Out of left field comes ... another pathetic attempt at diversion. Which
you lost several times over in those other threads. And to which I won't
bother to reply, because it is off-topic here.


{Mr. Lazio again deletes the evidence, in order to try to continue making
claims contrary to evidence.}
================================
JL:
In the outer reaches of galaxies, rotation curves are based on gas
velocities because there are no (or so few) stars from which to
obtain stellar velocities. However, I think it is the case that
within the optical disk, gas and stellar velocities match fairly
well.

greywolf42:
g You have no basis for this claim. There is not a single paper
g (...) for galactic rotation curves that does not depend on gas
g velocities or O and B stars. The O and B stars by necessity retain
g the initial velocities of the gas clouds which created them (...).
================================

Admittedly, this is not my area, but I'm astounded. Nobody's ever
attempted to measure the stellar velocity dispersion of a spiral
disk?

g That's a pretty silly strawman. Of course people have attempted to
g measure stellar velocity distribution. But it's very difficult
g (...) to do this on a star-by-star basis.
[...]

I see you can't disagree, so settled for deleting my clarifications.

This is done all the time for bulges and elliptical galaxies.

g Those use GAS when they can get it. It's only when gas is not
g available that one resorts to counting individual stars.

LOL! Mr. Lazio is really getting 'creative' in his deletions he
===========================================
JL:
Are
spiral disks really that faint that nobody's tried it even with nearby
galaxies?

*Read* my statement. They use the very luminous 'O' and 'B' stars when they
count. There aren't as many, and they are easy to pick out. Individual
stars dimmer than 'B' are difficult to pick out of the background star fog
in even nearby galaxies.
===========================================

Nobody counts individual stars in galaxies. Resolving a galaxy into
stars is only possible for the nearest galaxies.

And your point would be what? Nearby galaxies are included in the set of
all galaxies. In fact, I was dealing with your specific statement (which
you deleted).

What's measured is
the velocity dispersion from the integrated light of the stars.

Which is comprised primarily of O and B stars -- as they are several orders
of magnitude more luminous than the others.

This
is done all the time for elliptical galaxies and the bulges of spiral
galaxies (both of which often contain *little* gas).

And which don't contain the need for dark matter. It seems it's only
the gas measurements that require dark matter.


Moreover, as a counter-argument I'll point out the case of the
Galactic center (i.e., center of the Milky Way Galaxy). [...]
When stellar velocities became available, they matched the gas
velocities.

g Reference, please. I think you'll find that there are either NO
g stars or O and B stars.

[...]

Fascinating. Mr. Lazio feels the need to remove my statement:
"I'd be happy to be disproved. I've been asking for any paper to the
contrary for years."

Maybe it's because it severely weakens his case?

Where to start? There's a huge literature on the Galactic center.

I suggest looking at the ADS. Authors to search on include
K. Sellgren, R. Genzel, A. Ghez, J. Zhao, and P. Ho. The last two
have been more involved in determining the gas motions, while the
first three have been more involved in determining stellar motions.

g I'm not asking for general stratgies, but for specific references.
g I've done the usual searches. The point is, I believe that there
g aren't any stellar motion studies that don't either measure gas
g motions alone, or measure gas plus a few O and B stars.

That's why I referred specifically to Sellgren. She and her
collaborators have been measuring the stellar velocity dispersion from
late-type giants.

You didn't refer to *any* specific work by Sellegren. And why this bizarre
need to try to divert the issue to Sellgren on a subsequent post? Oh,
right, your first attempt (immediately below) showed the opposite of your
claim.

A good place to start might be Genzel et al. (1997, URL:


http://adsabs.harvard.edu/cgi-bin/np...NRAS.291..219G
) as they show a plot of the mass distribution in the Galactic
center as inferred from both stellar and gas motions (Figure 8).
They also have a summary of a number of observations in Section 1.
Also note that much of the stellar work they summarize or reference
concerns late-type stars.

g You're going to have to start reading abstracts a bit better (or
g perhaps you missed the fact that 'likely' early-type stars of 15-20
g solar masses are 'O' and 'B' stars). Here is the abstract [...]):

{I have no problem with Lazio deleting the abstract -- except that even the
abstract flatly disproved his claims.}

However I *do* have a problem with Mr. Lazio deleting my points
demonstrating that Lazio's own reference destroys his entire effort:
============================
1) "Compact radio source SgrA" indicates a *gas* measurement.
2) They 'may' have found an infrared signature of some stars.
3) However, they can only 'infer' that these are likely early-type stars
15-20 Msolar (i.e. 'O' and 'B' type stars).
4) There are 'several' fast-moving stars in the region. (They did not say
that they are *all* moving this fast.)
5) Using *theory* they then state that "there is no stable configuration of
normal stars, stellar remnants, or substellar entities at that density."
They ignore gas in this latter statement.

So, you'll note that my basic point is very well reinforced by your own
reference. We look at gas first, then -- sometimes, with difficulty --
manage to get a few very young 'O' and 'B' (recently condensed from gas) .
============================

g (the paper itself is not available on the website,)

The paper is indeed available on the Web site. See the links at the
top that say, "Full Refereed Journal Article" or "Full Refereed
Scanned Article."

And so I bid you adieu in this thread. I don't waste my time with
'creative' snippers. It is obvious that no amount of observational evidence
will change your view. You keep providing reference after reference that
contradicts your position. But you can't see it.

greywolf42
ubi dubium ibi libertas