Re a priori predictions, see, e.g., http://astroweb.case.edu/ssm/papers/GalMONDreview.pdfDrakkith said:I have a difficult time believe this. Do you have a reference supporting this?
A review is given of a priori predictions made for the dynamics of rotating galaxies. One theory — MOND — has had many of its predictions corroborated by subsequent observation. While it is sometimes possible to offer post hoc explanations for these observations in terms of dark matter, it is seldom possible to use dark matter to predict the same phenomena.
FWIW, Renzo's rule was not from a MOND paper. It was from: Dark Matter in Galaxies; Ryder, S.; Pisano, D.;. Walker, M.; Freeman, K., Eds., 2004, Vol. 220, IAU Symposium, p. 233, [astro-ph/0311348]. The paper is:PeterDonis said:I have only seen this rule claimed in papers that support MOND. I would want to see some indication from cosmologists who are not MOND proponents that this "rule" is actually a valid feature of the data before putting too much weight on it.
In the inner parts of spiral galaxies, of high or low surface brightness, there is a close correlation between rotation curve shape and light distribution. For any feature in the luminosity profile there is a corresponding feature in the rotation curve and vice versa. This implies that the gravitational potential is strongly correlated with the distribution of luminosity: either the luminous mass dominates or there is a close coupling between luminous and dark matter. In a similar way, the declining rotation curves observed in the outer parts of high luminosity systems are a clear signature of the stellar disk which either dominates or traces the distribution of mass.
The notion that the baryons are dynamically important in the centres of galaxies, including LSBs, undermines the whole controversy over the cusps in CDM halos and the comparison with the observations. If the baryons dominate in the central regions of all spirals, including LSBs, how can the CDM profiles be compared with the observations? Alternatively, if the baryons do not dominate but simply trace the DM distribution, why, in systems of comparable luminosity, are some DM halos cuspy (like the light) and others (also like the light) are not?
Hm, it looks like this paper is saying the rule only applies in the inner parts of spiral galaxies. I'll take a closer look when I get a chance.ohwilleke said:The paper is