In 2012 C Moni Bidin et al published work in which they essentially weighed the local dark matter by way of its effect on the kinematics of nearby stars. They analysed the trajectories of the stars and modeled their motions given various matter distributions. In the end they concluded that there was not as much dark matter present near our Sun as the basic assumption would predict.
Their approach was disputed by the work of Jo Bovy and Scott Tremaine 2. It was argued that Moni Bidin et al found the result they found due to their assumption of constant mean azimuthal velocity of the stars. More ore less, they argue, that Moni Bidin et al assumed circular orbits for the stars which may not be the case.
I must admit at this point, that I wrote an article informally defending Moni Bidin et al's work (Dark matter density near Earth? An informal defense of Moni Bidin et al. By Hontas Farmer | June 3rd 2012 05:06 PM | 7 comments | 2612 reads). I included many more details about the papers mentioned above in that blog posting which I will not repeat here. My criticism of Bovy and Tremaines work was that their analysis essentially assumed what it was trying to prove. They cited numbers derived from a paper where part of their analysis was the assumption of a spherical and uniformly dense halo of dark matter. Then fed those numbers into their analysis which was supposed to prove that there is a uniformly dense dark matter halo. So of course what did they find? ... A uniformly dense dark matter halo.
Now in 2014 Moni Bidin et al have taken account of the objections of Bovy and Tremaines 3 objections without their assumptions and claim to have shown that their first paper was essentially correct.
I'm sure there will be back and forth over this paper for years.
What this means for experiments like CDMS II, Xenon 100 and others like them.
If Moni Bidin et al are correct then it is very possible that dark matter searches conducted so far are about an order of magnitude less sensitive than they need to be. We perhaps should not have expected to detect dark matter in the Earth bound experiments conducted so far.
This means that not finding dark matter in those experiments may not be proof that dark matter does not exist.
I take it as an indication that dark matter may behave differently in the presence of relatively strong gravity 4. It may also be an indication that the notion of dark matter will have to be altered using some combination of modified gravity, extra fields and forces, and alternative types of dark matter.
The basic assumption of every dark matter direct detection search may be wrong. The papers below spell out possible reasons why and why not.
- "Kinematical and chemical vertical structure of the Galactic thick disk II. A lack of dark matter in the solar neighborhood" arXiv:1204.3942 The Astrophysical Journal, Volume 751, Issue 1, article id. 30, 14 pp. (2012). Moni Bidin et al
- "On the Local Dark Matter Density" arXiv:1205.4033 The Astrophysical Journal, Volume 756, Issue 1, article id. 89, 6 pp. (2012) Bovy and Tremaine
- "On local dark matter density" arXiv:1411.2625 Accepted for publication in Astronomy&Astrophysics; doi:10.1051/0004-6361/201424675 Moni Bidin et al
- "A Lagrangian which mathematically models Lambda CDM cosmology and explains the null results of dark astroparticle searches." Selected Works To appear in Science Open Research. H Farmer
Here is a good video on why one should almost never read them unless they want to hear something asinine.
Two old white men recreate a youtube comment thread where the commentators were clearly young women. (A little NSFW so be warned.)