New Paper: GR implies no dark matter

[selfAdjoint]

The new paper is titled
General Relativity Resolves Galactic Rotation Without Exotic Dark Matter


It is on the arxiv at http://www.arxiv.org/abs/astro-ph/0507619

From the abstract

A galaxy is modeled as a stationary axially symmetric pressure-free fluid in general relativity. For the weak gravitational fields under consideration, the field equations and the equations of motion ultimately lead to one linear and one nonlinear equation relating the angular velocity to the fluid density. It is shown that the rotation curves for the Milky Way, NGC 3031, NGC 3198 and NGC 7331 are consistent with the mass density distributions of the visible matter concentrated in flattened disks. Thus the need for a massive halo of exotic dark matter is removed. For these galaxies we determine the mass density for the luminous threshold as 10^{-21.75} kg.m$^{-3}.

 

[James R]

Sounds very interesting.

 

[ohwilleke]

To determine that the entire dark matter/MOND problem was simply a matter of a poor choice of how to simplify GR and that GR is really sufficient when a better model of how a galaxy should be treated under the equations is used, would be a dream come true. It isn't entirely clear to me, however, whether this is really a proper application of the GR equation, and whether this doesn't actually involve too many degrees of freedom. Still, it bears further examination.

A GR with cosmological constant solution is certainly far more attractive than a CDM lambda solution.

A second reason for skepticism is that it is my understanding that current apparent dark matter appears to have been confirmed by lensing data. And, the models used for lensing should not have the same infirmities as those used for galactic rotation modelling.

 

[Nereid]

Further, as has been pointed out several times, current good observational results suggest that most of the DM in rich clusters is in the ICM, not in galaxy halos.

Too, as ohwilleke has pointed out, the observational basis for DM galaxy halos isn't just rotation curves, there is a pretty strong signal from weak lensing too (e.g. the SDSS work) ... for avoidance of doubt though, this signal is seen only when data from thousands of galaxies is pooled.

 

[CarlB]

I'm no gravitation expert, but it seems to me that there was just a bit of a circular argument. It's like what was to be shown was that the stars move at a constant angular velocity (i.e. as an irrotational fluid) around the center of the galaxy, but the coordinates chosen made this assumption.

I think that they showed that under GR, if the stars did move as an irrotational fluid, then this would be consistent. What I would like to see added is some sort of analysis that assumed that the stars were moving with a slight deviation from irrotational, and then to derive that this deviation was stable or better, that it decayed away.

Carl

 

[wstevenbrown]

Coincidences:

1. Each galaxy is the dominant member of a sparse galaxy group.

2. Each galaxy is suspected of harboring a SMBH—M81 has two.

Consider the coincidences in the light of Karachentsev’s conclusions:

http://arxiv.org/astro-ph/0410065

It is tempting, when debunking the CDM hypothesis, to limit it by including in your assumption set the additional restraint that there can be only one particle type—Dr. K adds only one ‘epicycle’ to the hypothesis, a second DM particle type, to obtain consistent results for the virial masses and velocity dispersions of galaxies in sparse groups. While he did not explicitly consider galaxy rotation in this paper, the only area in which the CDM hypothesis is in deep trouble in this regard is WRT LSB galaxies. His coinvestigator, W.J.G. de Blok, has this to say:

http://arxiv.org/astro-ph/0506753


He does not suggest how to repair the halo models.

Over in the Universe Today forum, there’s a bloke who says all the answers lie in the ‘proper’ application of Newtonian gravity to obtain the mass distribution. His published works are on arxiv, also, but as a matter of interest, he has posted a $100000 reward for a disproof of his hypothesis.

http://www.universetoday.com/forum/index.php?showtopic=6923

Any takers? Best regards-- Steve