http://xxx.lanl.gov/PS_cache/astro-ph/pdf/0507/0507619.pdf

From a quick read they make a fatal mistake
in that luminous and non luminous matter are treated equally.

Even in this Solar System, Jupiter has a profound affect

They specifically use different analytical approaches to "solar systems" and "galactic systems"

Hi Mac,
Do you have any opinion to offer about the article? I guess you missed the other thread about it.

I've also found a number of follow-up articles which I haven't yet read (the first follow-up was mentioned in the previous thread. The others seem to have been written since then):

Singular disk of matter in the Cooperstock-Tieu galaxy model (http://arxiv.org/abs/astro-ph/0508377)
Presence of exotic matter in the Cooperstock and Tieu galaxy model (http://arxiv.org/abs/astro-ph/0510750)
The need for dark matter in galaxies (http://arxiv.org/abs/gr-qc/0511082)
Perspectives on Galactic Dynamics via General Relativity (http://arxiv.org/abs/astro-ph/0512048) (by the authors of the original paper)

From a quick read they make a fatal mistake
in that luminous and non luminous matter are treated equally.

Even in this Solar System, Jupiter has a profound affect

They specifically use different analytical approaches to "solar systems" and "galactic systems"

I think your presumption that they make a mistake, is a mistake. The differance between solar and galatic activity is a valid point to consider.

Hi Mac,
Do you have any opinion to offer about the article? I guess you missed the other thread about it.

I've also found a number of follow-up articles which I haven't yet read (the first follow-up was mentioned in the previous thread. The others seem to have been written since then):

Singular disk of matter in the Cooperstock-Tieu galaxy model (http://arxiv.org/abs/astro-ph/0508377)
Presence of exotic matter in the Cooperstock and Tieu galaxy model (http://arxiv.org/abs/astro-ph/0510750)
The need for dark matter in galaxies (http://arxiv.org/abs/gr-qc/0511082)
Perspectives on Galactic Dynamics via General Relativity (http://arxiv.org/abs/astro-ph/0512048) (by the authors of the original paper)

No I had not seen the other thread, nor other articles. I liked the method considerations and findings and felt the study was a good step forward.

Thanks for the links I will do more reading.

A quick read of these comments and rebuttals leaves me with the impression that the authors have a better grasp of the situation than the opposition.

Hum,
(i posted this somewhere else....)

Their model should be considered unphysical because:
1) Their nice fit to observed rotation curves is bad science - they are deriving the galactic density from the rotation curves when they should be doing it the other way around.
(i would also question their choice of the 4 galaxies they used in the study, which have rather steep orientations)
2) The theory fails to agree with observations near the galactic centre, which is why observations near the galactic centre have all been left off the graphs.
3) The theory fails when used in modelling the galactic rotation speeds of dwarf galaxies. None of the figures in the paper are for dwarf galaxies.
4) The use of "General relativity" is not the reason for their good fit. I can get an equally good fit using Newtonian mechanics.
5)They have replaced the dark matter with a `2D disk` that somehow possesses mass.


<SUP>This is not to say that General relativity is not as valid as Newtonian mechanics when dealing with such thing,
(as was clearly shown with the precession of mercury) but it too has limits.</SUP>

Hi blobrana,
In your opinion, do the modifications to the model in their follow-up paper fix any of these problems?

Sry,
haven't got round to it.

BTW, It just occurred to me that i posted a reply on this forum about gravitational lensed quasars showing how the can be used to indicate distance.
But, they can also show the mass of the intervening galaxy....

This is an independent way of measuring the hidden or `Dark` matter.

if i remember correctly they show that there is indeed 10 - 20 x more mass than is seen.

They can`t be both right (can they?)...

Sry,
haven't got round to it.

BTW, It just occurred to me that i posted a reply on this forum about gravitational lensed quasars showing how the can be used to indicate distance.
But, they can also show the mass of the intervening galaxy....

This is an independent way of measuring the hidden or `Dark` matter.

if i remember correctly they show that there is indeed 10 - 20 x more mass than is seen.

They can`t be both right (can they?)...

Pete: Is my memory failing or did not the authors address the gravitational lensing issue in their rebuttal?

Sry
has anyone got a link to the follow up paper fix....


@MacM
In the first paper they state:

“<i>Our masses are consistently lower than the masses projected by models invoking dark matter halos and our distributions roughly tend to follow the contours of the optical disks.</i>”

How did they manage to resolve the gravitational lensing issue?
If they use GR then surly a smaller mass will apparently `bend` light less...

Sure, Pete gave a link to the follow-up paper above. Here is a link to the pdf paper:
http://arxiv.org/PS_cache/astro-ph/pdf/0512/0512048.pdf

Cooperstock didn't address gravitational lensing in either paper. He focused solely on the 'flat' galactic rotation curves of four galaxies. A problem I see is that all galaxies do not have the same rotational curves, due obstensively to varying amounts of dark matter in different galaxies.

Hum,
i retract number 4 and 5)

They have not replaced the dark matter with a `massive 2D disk`.



BTW, here are two links for anyone who wants to know how a gravitational lens can work out mass and distance.

http://www.sdss.org/news/releases/20031217.lensing.html
http://spiff.rit.edu/classes/phys240/lectures/lens_results/lens_results.html