Galactic Rotation and Dark Matter

[dgruss23]

Thomas wrote: The downpoint is that at the moment non-peer-reviewed work is still classed as second-rate, but I hope this will soon change as well.

I'm in favor of the peer review system. The reason that non-reviewed work is seen as second class is not that it might not be good work, but that it hasn't passed that critical test of whether or not it is good work. The major problem I see with the peer review system is that there is a fine line between keeping the science in the journals sound and keeping work out simply because the conclusions are disagreed with. But I've learned a lot from having my papers reviewed.

[RickNZ]

At its core, the dark matter composition of the universe is something that theoriticians made up to explain the currently unexplainable.

How often has that been done in history of astrology?

Anything that attempts to dispel dark matter has my backing and interest.

[JS Princeton]

At its core, the dark matter composition of the universe is something that theoriticians made up to explain the currently unexplainable.

That's the story of all new science. Explaining the unexplainable. Just because it wasn't explained before doesn't make it wrong.

How often has that been done in history of astrology?

Don't really care. Astronomy is what I'm interested in.

Anything that attempts to dispel dark matter has my backing and interest.

That's a problematic point of view. One way to "dispel" dark matter would be to argue for creationism. Obviously this is a rather ludicrous tactic.

If you want to maintain an open mind like dgruss, thats' fine with me, but just declaring the dark matter paradigm to be wrong for no good reason is simply arguing without justification. If you have a particular beef beyond your simplistic "unexplainable" comment please feel free to share it with the rest of us.

[Spaceman Spiff]

There has been some discussion between Thomas and JS Princeton regarding recombination of electrons and ions. Unless I am misunderstanding what is being discussed, then JS may be missing the boat here. The recombination coefficient favors recombination to the ground state. For example, roughly half of all recombinations of hydrogen occur directly into the ground state. This is simply a re-statement of the Milne relation that relates photoionization (whose cross section goes as 1/n^5, where n is the principle quantum number) with its time reversal, recombination. If you'd like a reference, try Don Osterbrock's book on Nebular astrophysics, though this is pretty straightforward stuff. On the otherhand, maybe I am misinterpreting what is being discussed.

[Tim Thompson]

Wrong,if only you have read it the first time I post it it you will see how it really works. ...

I have read that paper, and i knbow very well what the critical ionization velicity is, and how & why it works. It is not physically applicable to the matter under discussion because (a) the Galactic magnetic field is way too weak, and (b) the relative velocity between the neutrals and the magnetic field is way too small.

Backward physics? Only if you view the problem from the wrong end. Assume you have a magnet with an electron moving in a circle around one of its field lines. Are you saying then that the electron would not move with the magnet if you move the latter?

Well, if you had a field strong enough to coerce an electron to move around just one field line, it probably would. But I don't think magnetic fields that strong can exist in nature.

What actually happens is that the electrons follow a path through the magnetic field that is derived from the vXB force, which changes the direction of the electron, but does not increase its energy. If you move the magnetic field, you can create an electric field such that delXE = -dB/dt, but the value of dB/dt depends on the relative motion between the electron and the B field. If you don't overcome the inertia of the electron, it will not move. And even if it does, it will lag behind the field.

You can't predict the behavior of a plasma (which is a collection of many charged particles) by analyzing the behavior of a single particle, since you need to include the coupling between particles, and the large fields created by large ensembles of charged particles. So you example is a poor analogy.

And your physics is backwards because you are not considering the energy of the plasma as compared to the energy of the field. If, for instance, you consider a 10^-6 Gauss field, the energy density is (1/2)B^2 (in Gaussian units), which works out to 5x10^-13 erg/cm^3. On the other hand, the energy density of a 1 particle per cubic centimeter plasma with kinetic energy 1 ev is about 1.6x10^-12 erg/cm^3, and that's just the kinetic energy, no electric or mangetic fields considered yet. The plasma will have a considerably higher energy density than the field, so the plasma will push the field around, not the other way around. Besides, it's a natural consequence of Alfven's frozen flux theorem (see, for instance, The Physics of Plasmas, Boyd & Sanderson, Cambridge University Press, 2003, section 4.2; Magnetic Reconnection, Priest & Forbes, Cambridge University Press, 2000, section 1.4).

The only place where you see the field push the plasma around is in the tenuous halo of the Galaxy, where the plasma density is too small, and electrons spiral to high galactic latitude along the magnetic field.

[Tim Thompson]

At its core, the dark matter composition of the universe is something that theoriticians made up to explain the currently unexplainable.

No, it was "made up" to explain something that is curently unexplained, not unexplainable. And what is wrong with dark matter? Why can't matter be dark? What fundamental property of nature, what fundamental law of physics, prohibits any matter from being dark? In the absence of such a fundamental argument, dark matter is by far the most scientific, and simplist explanation there is. If you want to exercise the edge of Occam's razor, dark matter wins every time.

[kilopi]

No, it was "made up" to explain something that is curently unexplained, not unexplainable. And what is wrong with dark matter? Why can't matter be dark? What fundamental property of nature, what fundamental law of physics, prohibits any matter from being dark? In the absence of such a fundamental argument, dark matter is by far the most scientific, and simplist explanation there is. If you want to exercise the edge of Occam's razor, dark matter wins every time.

But, the dark matter would be something we've never seen before, a type of matter that we're probably not familiar with, or interacting in a mechanism that we've not noticed before, right?

[D J]

Wrong,if only you have read it the first time I post it it you will see how it really works. ...

I have read that paper, and i knbow very well what the critical ionization velicity is, and how & why it works. It is not physically applicable to the matter under discussion because (a) the Galactic magnetic field is way too weak, and (b) the relative velocity between the neutrals and the magnetic field is way too small.

The only place where you see the field push the plasma around is in the tenuous halo of the Galaxy, where the plasma density is too small, and electrons spiral to high galactic latitude along the magnetic field.

But the gas even if it is partly ionized is affected the magnetic field.

Could it be possible than this Alfven's frozen flux theorem keep the momentum for the rotation?Ie the magnetic field being trapped the energy have to go somewhere so making the rotation we observe.

And as suggested in the links below the mass of the galaxy could have been over estimated from the rotation assuming gravity being the only cause for the rotation.

I suggest than you read these two links provided by dgruss23

http://adsabs.harvard.edu/cgi-bin/np...e5c03c80a10525

http://adsabs.harvard.edu/cgi-bin/np...e5c03c80a10525

[Thomas]

Check out my website http://www.plasmafacts.de . This sums up most of my works in quite some detail and you can also download the full manuscripts for the major ones (it does not really matter which ones are actually published in print

Sure it matters, especially since you've made the claim. I see three published papers listed on your cv.

The 2 papers co-authored by me do not really count in this context, because I did neither write them nor dealt with the referees (I was merely responsible for the computational physics and data analysis). These publications are scientifically unimportant anyway. My controversial work started only with my Ph.D. thesis and from then on I have only written as a sole author (partially because of the controversial material, but also because of some trouble with the co-authors in one of the earlier publications).

[Thomas]

Backward physics? Only if you view the problem from the wrong end. Assume you have a magnet with an electron moving in a circle around one of its field lines. Are you saying then that the electron would not move with the magnet if you move the latter?

Well, if you had a field strong enough to coerce an electron to move around just one field line, it probably would. But I don't think magnetic fields that strong can exist in nature.
What actually happens is that the electrons follow a path through the magnetic field that is derived from the vXB force, which changes the direction of the electron, but does not increase its energy. If you move the magnetic field, you can create an electric field such that delXE = -dB/dt, but the value of dB/dt depends on the relative motion between the electron and the B field. If you don't overcome the inertia of the electron, it will not move. And even if it does, it will lag behind the field.

It will only lag behind by one Larmor circle, which is negligible compared to galactic dimensions.

And your physics is backwards because you are not considering the energy of the plasma as compared to the energy of the field. If, for instance, you consider a 10^-6 Gauss field, the energy density is (1/2)B^2 (in Gaussian units), which works out to 5x10^-13 erg/cm^3. On the other hand, the energy density of a 1 particle per cubic centimeter plasma with kinetic energy 1 ev is about 1.6x10^-12 erg/cm^3, and that's just the kinetic energy, no electric or mangetic fields considered yet. The plasma will have a considerably higher energy density than the field, so the plasma will push the field around, not the other way around.

A plasma density of 1 cm^-3 is pretty unlikely. I would assume something like 10^-3 cm^-3 which makes the plasma energy negligible (even though I would assume 10 eV electrons).
Anyway, the magnetic field here is assumed to be associated with the plasma of the core region of the galaxy, i.e. the plasma in the outer region (where the anomalies in the rotation curves are observed) is being pushed by the plasma in the inner region via the magnetic field. I can not really see this work the other way around.

[dgruss23]

Thomas wrote: Anyway, the magnetic field here is assumed to be associated with the plasma of the core region of the galaxy, i.e. the plasma in the outer region (where the anomalies in the rotation curves are observed) is being pushed by the plasma in the inner region via the magnetic field. I can not really see this work the other way around.

Could matter be pushed outward? If so this might provide an observational test.

[kilopi]

The 2 papers co-authored by me do not really count in this context, because I did neither write them nor dealt with the referees (I was merely responsible for the computational physics and data analysis). These publications are scientifically unimportant anyway. My controversial work started only with my Ph.D. thesis and from then on I have only written as a sole author (partially because of the controversial material, but also because of some trouble with the co-authors in one of the earlier publications).

So, the paper that you mentioned that you wrote and had accepted by a peer-reviewed journal was Scattering of Radio Waves by High Atomic Rydberg States. Radio Science 28,3,361,S93-001, in 1993? Radio Science is an American Geophysical Union journal, right?

[JS Princeton]

The recombination coefficient favors recombination to the ground state. For example, roughly half of all recombinations of hydrogen occur directly into the ground state. This is simply a re-statement of the Milne relation that relates photoionization (whose cross section goes as 1/n^5, where n is the principle quantum number) with its time reversal, recombination. If you'd like a reference, try Don Osterbrock's book on Nebular astrophysics, though this is pretty straightforward stuff. On the otherhand, maybe I am misinterpreting what is being discussed.

I think there's an issue of misinterpretation. I'm saying that the reason that Stromgren Sphere's exist is because the effective recombination coefficient (for the cloud) is preferential toward the cascade shower for recombination into an upper state because that releases a lower energy photon. The problem with straight recombination to the ground state is that that it releases an equally energetic photon that simply reionizes another nearby atom. It's all about HII regions.

[Tim Thompson]

But the gas even if it is partly ionized is affected the magnetic field.

But only the ionized fraction. We know that the bulk of the ISM in the disk of the Galaxy is neutral. Unless the plasma is dense enough to be collisional, there is no mechanism to transfer the energy from the ionized part to the majority neutral part. Most ISM plasma is not collisional because it's too sparse.

Could it be possible than this Alfven's frozen flux theorem keep the momentum for the rotation?Ie the magnetic field being trapped the energy have to go somewhere so making the rotation we observe.

It could if the field were strong enough, and if the plasma were collisional enough to energize the neutrals. But neither of those is in fact the case.Alfven's frozen flux theorem shows that the magnetic flux is trapped by the plasma, and it will go where the plasma goes, not the other way around. The plasma drags the field. This is especially true in the disk of the Galaxy, where the plasma density & field strength are both rather higher.

I suggest than you read these two links provided by dgruss23.

Have you read them? Did you know what they say, before asking me to read them? Let's see ...

Galactic magnetism and the rotation curves of M31 and the Milky Way
J.P. Vallee
Astrophysical Journal, Part 1, 437(1): 179-183, December 1994
Abstract: Can a magnetic field in a spiral galaxy speed up the interstellar gas in its circular galactic rotation, faster than the stars move around the galaxy? If so, a recently proposed magnetic-support model for a faster gas could explain the flat-type rotation curves of the interstellar gas moving around a galaxy's center, rendering dark matter unnecessary. But how strong must this magnetic field be? I find that in M31 and the Milky Way, the predicted magnetic field strengths (for magnetic support of the gas) are a factor more than 2 times the observational values. The predicted magnetic energies are a factor more than 4 times the observed magnetic energies. These observations contradict the magnetic-support theory of the gas, in M31 and the Milky Way.

OK, that paper says that the observed magnetic energies are 4 times too small for the field to move the plasma. And how about the other paper?

Dark matter, not magnetism
Massimo Persic & Paolo Salucci
Royal Astronomical Society, Monthly Notices 261(3): L21-L24, April 1993
Abstract: Battaner et al. (1992) argued that IMFs can significantly affect the circular motion of gas in spiral galaxies and explain their observed flat rotation curves. This interpretation of galaxy kinematics challenges the conventional dark matter (DM) picture. However, the evidence for DM in galaxies is not restricted to gas motions. Measurements of velocity differences within galaxy pairs (not based on gas rotation and hence not affected by magnetic fields) imply the existence of massive halos, whose properties are in total agreement with those derived from the DM interpretation of the observed rotation curves. On the other hand, the predictions of the magnetic-field, no-DM scenario cannot be reconciled with observations of pairwise galaxy dynamics. We discuss the above opposing views of galaxy kinematics. After giving substantial support to the conventional view that DM plays the key dynamical role on galactic scales, we turn the argument devised to test the Battaner et al. theory into a powerful tool to investigate the properties of DM haloes on scales of several hundred kpc.

Well, this one even says "Dark matter, not magnetism" in the title. And they say that "On the other hand, the predictions of the magnetic-field, no-DM scenario cannot be reconciled with observations of pairwise galaxy dynamics."

Both papers clearly support what I have said all along. The magnetic field strengths are too low, the magnetic fields cannot be responsible for the effects interpreted as "dark matter".

[D J]

http://adsabs.harvard.edu/cgi-bin/np...e5c03c80a10525

I forget to tell than i have based my reply on the scanned version of the abstract not on the resume of the abstract.Sorry about that.

[Tim Thompson]

A plasma density of 1 cm^-3 is pretty unlikely.

That density is typical of the hot ionized medium or coronal gas of the Galaxy. It has a scale height of about 3000 pc above & below the disk of the Galaxy, but carries only a few percent of the mass of the Galaxy. The warm ionized medium has a scale height of about 1000 pc, and a density of about 0.15 electrons per cm^3. The warm neutral medium has a scale height of 500 pc, and has a density of 0.5 to 1.0 electrons per cm^3. These are the diffuse components of the interstellar medium. About 50% of the mass of the ISM is made up of the combined "warm" media, about 2/3 of that is neutral. About 25% of the ISM mass is in the form of cold neutral hydrogen (HI) clouds, with particle densities anywhere from 10 to 1000 atoms per cm^3. Most of the remaining 25% of the ISM mass is in cold molecular clouds, with densities as high as 10,000 molecules per cm^3.

The hot coronal gas, the gas you described as 10^-3 /cm^3 and maybe 10 ev temperature (the cornonal gas temperature is closer to 100 ev), only accounts for a few percent of the mass, and most of that extends well beyond the disk of the galaxy. So only a few percent of a few percent of the mass of the Galaxy will have an opportunity to exchange energy with the disk, through a yet to be determined mechanism. This is not a very promising adventure.

Better to try to couple the field to the more dense disk, but then you run into the problem that the bulk of the disk mass is neutral, and won't couple to the magnetic field. And, as my response to Orion38 points out, the published studies show that the observed magnetic field strengths are too low to support the flat rotation curves.

[D J]

Here an interesting model
A two-dimensional model of magnetohydrodynamically driven rotation of spiral galaxies without dark matter

A steady-state two-dimensional model of the outermost region of a spiral galaxy is presented. The magnetic field, which is able to explain the flat rotation curve, is calculated, without the existence of any kind of dark matter. The vertical and radial distributions of the density are calculated, as well as the radial and vertical velocities. The magnetic field strength is noticeably constant in the peripheral disc, at about 7x10^-7 gauss, much more moderate than that obtained in our previous model (Battaner et al.). The vertical velocities are driven by Parker's instabilities and induce a moderate escape of gas of about 0.1 M_solar yr^-1 which prevents excessive flaring.
http://adsabs.harvard.edu/cgi-bin/np...29B&db_key=AST

Others:
http://adsabs.harvard.edu/cgi-bin/np...ONS&db_key=AST

[RickNZ]

Your being overly and unjustifiably defensive here JS.

[JS Princeton]

Astrophysics and Space Science
249 (2): 223-226, 1997
Copyright © 1997 Kluwer Academic Publishers
All rights reserved
Comments on the Magnetic Alternative to Missing Mass

F. J. Sánchez-Salcedo
Abstract unavailable at adsabs, so I provide it here:

Instituto de Astrofísica de Andalucía. Csic. Sancho Panza, s/n, P.O. Box 3004, 18080 Granada, Spain Fax: 34-58-81 45 30; Internet: javier@iaa.es

Abstract

The arguments against the magnetic alternative given by Katz (1994) are discussed. Our conclusion is that the major problem regarding this alternative to dark matter is the flaring of the disk as suggested by Cuddeford and Binney (1993). We propose that the study of the equilibrium in the vertical direction should be carried out in dwarf spirals. Magnetic tension could alter the rotation curve of spiral galaxies but is not able to eliminate the necessity of dark matter.

Article ID: 137147

This is the biggest problem with magnetic alternatives. It is poorly dealt with in the article you cite, Orion.

[D J]

Astrophysics and Space Science
249 (2): 223-226, 1997
Copyright © 1997 Kluwer Academic Publishers
All rights reserved
Comments on the Magnetic Alternative to Missing Mass

F. J. Sánchez-Salcedo
Abstract unavailable at adsabs, so I provide it here:

Instituto de Astrofísica de Andalucía. Csic. Sancho Panza, s/n, P.O. Box 3004, 18080 Granada, Spain Fax: 34-58-81 45 30; Internet: javier@iaa.es

Abstract

The arguments against the magnetic alternative given by Katz (1994) are discussed. Our conclusion is that the major problem regarding this alternative to dark matter is the flaring of the disk as suggested by Cuddeford and Binney (1993). We propose that the study of the equilibrium in the vertical direction should be carried out in dwarf spirals. Magnetic tension could alter the rotation curve of spiral galaxies but is not able to eliminate the necessity of dark matter.

Article ID: 137147

This is the biggest problem with magnetic alternatives. It is poorly dealt with in the article you cite, Orion.

Not only the article you cite don`t dealt with the paper i cite.
In fact the paper I quote SOLVE the argument about the flaring of the disk.


http://adsabs.harvard.edu/cgi-bin/np...29B&db_key=AST

[JS Princeton]

Orion, your argumentative posturing has just dug your own grave.

The fact of the matter is, I got this paper out because it cites your paper and shows that its analysis isn't correct: its proposed solution for the flaring disk really is not a solution at all because of some major flaws in their assumptions about the coupling of magnetic moments to the angular momentum of a rotating galaxy.

Try again.

[D J]

Orion, your argumentative posturing has just dug your own grave.

The fact of the matter is, I got this paper out because it cites your paper and shows that its analysis isn't correct: its proposed solution for the flaring disk really is not a solution at all because of some major flaws in their assumptions about the coupling of magnetic moments to the angular momentum of a rotating galaxy.

Try again.

Quote from the paper you cite
The arguments against the magnetic alternative given by *Katz (1994)* are discussed.
Our conclusion is that the major problem regarding this alternative to dark matter is the flaring of the disk as suggested by *Cuddeford and Binney* (1993).

The article i present is about the paper of Battaner E Florido E
So the analysis from your paper dind`t dealt with the article presented by those authors.
http://adsabs.harvard.edu/cgi-bin/np...29B&db_key=AST

The magnetic field strength is noticeably constant in the peripheral disc, at about 7x10^-7 gauss, much more moderate than that obtained in our previous model (Battaner et al.). The vertical velocities are driven by Parker's instabilities and induce a moderate escape of gas of about 0.1 M_solar yr^-1 which prevents excessive flaring.

[Tim Thompson]

Abstracts are good if you want to see the highlights, and decide perhaps, whether or not to read the paper. However, if you are going to start making definitive arguments, it's necessary to read the papers. i have done that, and come to the conclusion that the magnetic field explanation for galaxy rotation curves remains dubious.

A two-dimensional model of magnetohydrodynamically driven rotation of spiral galaxies without dark matter, Battaner & Florido, Monthly Notices of the Royal Astronomical Society 277: 1129-1133, 1995.
This is the paper cited by Orion38. In this paper the authors conclude as follows: "The main conclusion is the confirmation that the magnetic support hypothesis may provide a way to explain the rotation curve of spiral galaxies, without invoking the existence of dark matter." However, on reading the paper one finds that there are no sample rotation curves presented. All of the discussion centers around the flaring of the disks. The theory is used to compute disk flaring, but there are no comparisons between the model output, and observed flaring. On page 1132 (text & figure 2), the authors show that the flaring function produces a scale height of about 3 kpc at a radial distance of 15 kpc, and a scale height just over 7 kpc, at a radial distance of 30 kpc. The scale height is about 5 kpc at a radial distance of 20 kpc. The authors state that these numbers are "very reasonable."

Flat Rotation Curves, Inverse Cascade, and Magnetic Fields, F. Javier Sanchez-Salcedo, Astrophysical Journal 467: L21-L24, August 10, 1996.
This paper is in response the the 1995 Battaner & Florido paper, as well as some others. As the Battaner & Florido paper, the author points out that flaring in the Milky Way produces a scale height of about 600 pc at a radial distance of 20 kpc, far below the 5 or so kpc from the Battaner & Florido paper. Despite their "very reasonable" conclusion, Sanchez-Salcedo shows that there is a stark contrast between flaring in the Battaner & Florido model, and flaring as observed, both in the Milky Way and in M81. Already we have reason to lose confidence in the Battaner & Florido conclusions.

On the role of magnetic fields in H I rotation curves, F. Javier Sanchez-Salcedo, Monthly Notices of the Royal Astronomical Society 289: 863-868, 1997.
in this paper, Sanchez-Salcedo expands on the previous paper, returning once again to the Battaner & Florido paper as well. The author deomonstrates a model which includes (a) magnetic field about 1 microgauss, (b) observable (luminous) matter, and (c) a dark matter halo. The model is used to generate a theoretical rotation curve for NGC 1560, which is compared to the observed rotation curve (NGC 1560 was chosen because its rotation curve shows some structure, and is therefore a more complicated test of the theory). The result is that ignoring the magnetic field, as is normally done, does not produce a good rotation curve. Including a magnetic field ranging from 0.5 to 2 microgauss produces an excellent fit, but only in the presence of a dark matter halo. So, while the magnetic field cannot be ignored, it can also not eliminate the need for a dark matter halo, at least in the case of NGC 1560. The author points out other galaxies, where the rotation curves can be well fit without mangetic fields. So the involvement of the magnetic field in the rotation curve appears not to be universal, but a function of some other propery, perhaps the overall mass of the galaxy.

I can find no indication of any response to these paper by Battaner & Florido.

My conclusion, from reading these 3 papers, is that the magnetic support hypothesis is overplayed by Battaner & Florido. They claim to be able to do away with dark matter entirely, but this claim does not stand up to examination. On the other hand, it also appears that magnetic fields, at least in some cases, do play a role in establishing flat rotation curves for spiral galaxies. And it remains the case that dark matter haloes are required, in all examples, to establish flat rotation curves that match observation.

[D J]

Tim Thompson wrote:
"And it remains the case that dark matter haloes are required, in all examples, to establish flat rotation curves that match observation."
--
In fact what it -remains- is that the dark matter hypothesis is the perfect "fudge factor".It is easier to patch up the Big Bang theory with invisible entities.
How can you challenge an invisible entity who was created to fit the missing mass every time you need it?
The truth is that after more than 30 years looking for it there is still no definitive proof of its existence. :wink:

[Thomas]

Thomas wrote: Anyway, the magnetic field here is assumed to be associated with the plasma of the core region of the galaxy, i.e. the plasma in the outer region (where the anomalies in the rotation curves are observed) is being pushed by the plasma in the inner region via the magnetic field. I can not really see this work the other way around.

Could matter be pushed outward? If so this might provide an observational test.

There have been results published recently that show a corresponding outflow of hot gas from galaxies (it was reported in the New Scientist). This was in connection with an attempt to explain the temperature of the intergalactic medium (according to their theory the source is supernovae).

[Thomas]

A plasma density of 1 cm^-3 is pretty unlikely.

That density is typical of the hot ionized medium or coronal gas of the Galaxy.

Are you sure, you are not mixing up neutral and plasma densities here ? The average interstellar neutral gas density in our galaxy is generally assumed to be 1 cm^-3, and for a 50% degree of ionization you would then need a UV radiation flux of something between 10^5 to 10^9 ph/cm^2/sec (depending on what values you use for the recombination coefficient in the equation for ionization-recombination equilibrium
alpha*n^2=N*F*sigma
where alpha is the recombination coefficeint, n the plasma density, N the neutral density, F the radiation flux and sigma the photoionization cross section).
As calculated earlier in this thread (by using the solar UV flux) the interstellar flux should probably be of the order of 10 ph/cm^2/sec which would give you at best a density n=10^-2 cm^-3 if N=1cm^-3 (10^-4 cm^-3 if you use the recombination cross section from my theory).
Anyway, if you assume a gas density of 1 cm^-3 throughout our galaxy, you will find that this corresponds to a mass identical to the mass of all the stars (10^11 solar masses), which I think is a rather unlikely scenario both for the plasma and neutral gas (you would have to ask yourself why such a huge mass has not become gravitationally unstable and formed into stars itself; in my opinion the total mass of the gas definitely has to be much smaller than the mass of the stars).

[JS Princeton]

Tim Thompson wrote:
"And it remains the case that dark matter haloes are required, in all examples, to establish flat rotation curves that match observation."
--
In fact what it -remains- is that the dark matter hypothesis is the perfect "fudge factor".It is easier to patch up the Big Bang theory with invisible entities.

This is putting the cart before the horse. The Big Bang doesn't require dark matter to survive. It's a free parameter.

How can you challenge an invisible entity who was created to fit the missing mass every time you need it?

It wasn't created, it was dynamically favored because there is no other force that allows for consistent acceleration. Magnetism doesn't quite do it because the 10^-6 Gauss fields in interestellar space can only accelerate the constituents in a flat curve if you get the flaring solution (due to the magnetic field line reconnection that is what you ALWAYS get whenever you combine angular momentum with magnetic fields). The proposed solution to this, that of some unobserved magnetic field line drift, doesn't pan out. We see magnetic reconnection in all smaller scale astrophysics but denying its existence on the galactic scale is simply thrusting one's head in the sand.

The truth is that after more than 30 years looking for it there is still no definitive proof of its existence. :wink:

Orion, who made you the arbiter of definitive proof? I don't have definitive proof that you exist, but I still think the evidence is good for your existence.

[JS Princeton]

Anyway, if you assume a gas density of 1 cm^-3 throughout our galaxy, you will find that this corresponds to a mass identical to the mass of all the stars (10^11 solar masses), which I think is a rather unlikely scenario both for the plasma and neutral gas (you would have to ask yourself why such a huge mass has not become gravitationally unstable and formed into stars itself; in my opinion the total mass of the gas definitely has to be much smaller than the mass of the stars).

No, the mass of the gas is about equal to the mass of stars. Don't take my word for it, look it up for yourself.

The huge mass has become gravitationally unstable. That's why we have stars in the first place. Other dynamics prevent the entire ISM material from coalescing (in particular, shock dynamics and solar winds).

[Tim Thompson]

Are you sure, you are not mixing up neutral and plasma densities here ?

My phrase "that density" was intended to refer to your cited density of 10^-3 per cm^3. But I see from my own post that I failed to make that point. So, for the record, what I meant to say was that 10^-3 per cm^3 is the density typical of the hot ionized medium. You can see in the body of my message, that I do give the densities of the various media explicitly.

Anyway, if you assume a gas density of 1 cm^-3 throughout our galaxy, you will find that this corresponds to a mass identical to the mass of all the stars (10^11 solar masses), which I think is a rather unlikely scenario ...

At least partly correct, in that the ISM mass is generally only a few percent of the stellar mass, in the inner regions, but the gas can be as high as 15% of the mass in the outer regions of the galaxy. But this varies greatly from place to place; in the vicinity of the sun, it's about 20% gas, 40% stars, and 40% dark matter (Dynamics of Galaxies, Giuseppe Bertin, Cambridge University Press 2000; The Milky Way as a Galaxy, Gilmore, King & van der Kruit, University Science Books, 1990).

But this does raise another interesting issue. An ~1 microgauss magnetic field may be responsible for flat rotation curves (though it seems unlikely, as per my earlier response to Orion38). But those rotation curves are derived from observations of gas. What about stars? That kind of a magnetic field won't push stars around, and neither will the mass of the ISM. So, for the solar neighborhood, where the mass model is built from stellar kinematics, and still requires about 40% dark matter, how does a magnetic field figure in that mass model?

Added comment: A recent paper studying the 3-D mass distribution in the Milky Way reports the neutral hydrogen (HI) gas mass inside a 17 kpc radius to be 2.5x10^9 solar masses, about 1.5% of the total dynamical mass (Three-dimensional distribution of the ISM in the Milky Way Galaxy: I. The H I disk, H. Nakanishi H & Y. Sofue, Publications of the Astronomical Society of Japan 55(1): 191-202, 2003). Another recent paper establishes a lower limit for the dynamical mass of the Milky Way at 2.2x10^12 solar masses, from the dynamics of 11 satellite galaxies, 137 globular culsters, and 413 field halo stars (The mass of the Milky Way: Limits from a newly assembled set of halo objects, T. Sakamoto, M. Chiba & T.C. Beers, Astronomy and Astrophysics 397(3): 899-911, January 2003.

[Tim Thompson]

In fact what it -remains- is that the dark matter hypothesis is the perfect "fudge factor".It is easier to patch up the Big Bang theory with invisible entities.

Very wrong, for two very big (and obvious) reasons.

First, whether or not galaxy rotation curves require dark matter to explain them is entirely independent from any consideration of Big Bang cosmology. They have nothing to do with each other beyond a very superficial level. So there is no question about "saving" Big Bang cosmology, and your comment is pointless.

Second, dark matter is not a "fudge factor" by any stretch of the imagination. A "fudge factor" is a number which has no physical significance, and is simply stuck into an equation so that its arithmetic agrees with what you want it to say. Dark matter, on the other hand, is a perfectly reasonable physical explanation for the observed phenomena. I have asked repeatedly for someone to show me the fundamental physical principle that prevents matter from being "dark". Can you tell me why all matter absolutely must be visible? That's the only difference between "normal" matter & "dark" matter, and I can see no sense at all behind the extreme desire to avoid the idea of dark matter at any logical cost.

How can you challenge an invisible entity who was created to fit the missing mass every time you need it? The truth is that after more than 30 years looking for it there is still no definitive proof of its existence.

None of this makes any sense at all. Dark matter is not "invisible", it's just "dark". There are other ways to see things that are dark, and dark matter is no exception to the rule. It's just a matter of figuring out how to detect it, and there are numerous teams working on the problem now. Dark matter will eventually be detected, it's just a matter of time.

As for "definitive proof", we all know that's a dodgy concept in the natural sciences. Almost nothing is subject to "definitive proof". The real operating goal is evidentiary support. There is, in fact, a great deal of evidence, all of which points towards the existence of dark matter. One piece of that evidence is flat rotation curves, which you have already seen, cannot be explained by using magnetic fields. But there is also the dynamics of galaxies in a cluster, which returns the cluster mass. Will you now claim that the cluster magnetic field is pushing the galaxies around too? Even here in the Milky Way, in the solar neighborhood, we know that the dynamic mass is about 40% dark matter, so what do you think is pushing the stars around? And, of course, the anisotropies in the cosmic microwave background imply a non-baryonic dark matter as well.

The real beauty of the dark matter hypothesis is that, with nothing more than a minor extension of what we already know, just one ingredient in the cosmic kitchen, simultaneously explains a long list of observed "anomalies". If you think that dark matter is such a lousy idea, where's your better idea? We already know it can't be magnetic fields, so what do you think is simpler than matter that happens to be dark?