Parallel Dark Matter

Parallel Dark Matter 9

Previously

I have been blogging about a theory I call Parallel Dark Matter (and here and here), which I may not be the first to propose, though I seem to be the first to flesh the idea out.

In particular, I mentioned recent news that the solar system appears devoid of dark matter, something that PDM predicted and no other dark matter theory did.

Watch that title!

So I wes very surprised to read Plenty of Dark Matter Near the Sun (or here). It appeared to contradict not only the earlier success of PDM but also the recent observations.

But when I got the paper that the article is based on (here and from the URL it looks like arXiv has it too), the abstract immediately set the record straight.

By "near the sun", they don't mean "in the solar system" like you might think. They mean the stellar neighborhood. It's not immediately obvious just how big a chunk of stellar neighborhood they are talking about, but you may get some idea from the fact that their primary data is photometric distances to a set of K dwarf stars.

The paper

Silvia Garbari, Chao Liu, Justin I. Read, George Lake. A new determination of the local dark matter density from the kinematics of K dwarfs. Monthly Notice of the Royal Astronomical Society, 9 August, 2012; 2012arXiv1206.0015G (here)

But that's not the worst

science20.com got it worse: "Lots Of Dark Matter Near The Sun, Says Computer Model". No and no. They used a simulation of dark matter to calibrate their mass computations. They did not draw their conclusions from it.

And the Milky Way's halo may not be spherical

The most interesting bit IMO is that their result "is at mild tension with extrapolations from the rotation curve that assume a spherical halo. Our result can be explained by a larger normalisation for the local Milky Way rotation curve, an oblate dark matter halo, a local disc of dark matter, or some combination of these."