Monday, February 04, 2008

More Problems With MOND

There are more challenges to the Modified Newtonian Dynamics (MOND) theory.

[Note: a few of the links may require free registration to gain full access to the article]

First of course was the observation from the collision in the Bullet cluster from a year ago. The result from this strongly favors the presence of Dark Matter. In fact, many astrophysicists even proclaimed that MOND is dead after this observation. Of course, things don't die off that easily (and that fast) in physics. The MOND advocates came back with a scenario that could be consistent with the Bullet cluster observation without any need for Dark Matter. This was met with major skepticism by others in the field, as can be read at the end of that article in the link.

Now comes another publication that might seriously challenge MOND's analysis of the Bullet cluster.

I. Ferreras et al., "Necessity of Dark Matter in Modified Newtonian Dynamics within Galactic Scales", Phys. Rev. Lett. v.100, p.031302 (2008).

Abstract: To test modified Newtonian dynamics (MOND) on galactic scales, we study six strong gravitational lensing early-type galaxies from the CASTLES sample. Comparing the total mass (from lensing) with the stellar mass content (from a comparison of photometry and stellar population synthesis), we conclude that strong gravitational lensing on galactic scales requires a significant amount of dark matter, even within MOND. On such scales a 2 eV neutrino cannot explain the excess of matter in contrast with recent claims to explain the lensing data of the bullet cluster. The presence of dark matter is detected in regions with a higher acceleration than the characteristic MOND scale of ~10^-10 m/s^2. This is a serious challenge to MOND unless lensing is qualitatively different [possibly to be developed within a covariant, such as Tensor-Vector-Scalar (TeVeS), theory].

This lensing issue was brought up in one of the article that I linked above, so obviously, this is a serious issue with MOND. Let's see if they can dig out of this one.


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