Friday, April 19, 2013

Local Dark Matter Density

A detailed model of the inferred dark matter halo of the Milky Way galaxy based on the observed motions of stars in our galaxy implies that the density of dark matter in the vicinity of our solar system is 0.49 +0.08/-0.09 GeV/cm^3. 

If a dark matter particle is 2 keV as implied by other studies, then the density in dark matter particles per volume in this vicinity of the galaxy is 245,000 per cm^3, which is 245 dark matter particles per millimeter^3.

At an 8 GeV mass (which is disfavored by other measurements) there would be one particle per sixteen cm^2 (about one per cubic inch).  At an 130 GeV mass (also disfavored by other measurements) there would be one particle per 260 cm^3 (a cube slightly more than 6 cm on each side).


Mitchell said...

If we assume that warm dark matter is correct, then there ought to be a dominant keV component to the dark matter.

Regarding CDMS-II's 8 GeV signal, I like your observation that an unstable particle like the 8 GeV neutrinos of the nuMSM could be produced by cosmic rays. But someone needs to check whether the CDMS-II event rate would then make sense...

130 GeV, similarly, derives just from a few dozen gamma rays observed by Fermi. It could derive from a heavy stable component of the DM that is only a very small fraction of the total mass, but which congregates in a small volume (galactic center?) for astrophysical reasons... It's also intriguingly close to the Higgs mass, but I don't think anyone has a good model for what that could mean.

"A Theory of Dark Matter" by Arkani-Hamed et al lists a few other astrophysical signals which may or may not be DM.

Mitchell said...

By the way, Marni Sheppeard is blogging again, at "Arcadian Omegafunctor". She's talking about MOND lately.

andrew said...

Thanks for the tip. Glad to hear it.