# Distribution of dark matter

How is dark matter distributed (as far as we know)?

Let's stay with a single galaxy like the Milky Way. I heard that dark matter is even more concentrated in the center than in the halo, that it is falling off when moving outside, but since the halo is so huge (how huge, ten times larger?) most dark matter can be found there. Is that correct?

So there is dark matter also in our solar system. But by what density? If the density would be high, we would have noticed it by the motion of the planets or nearby stars. Can the effect of dark matter only be seen at larger distances where it accumulates despite its low density?

thanks!

phyzguy
What you said is largely correct. There's lots of work to understand the Milky Way dark matter halo. One model (see this paper) is a density profile like:
$$\rho_{DM} = \rho_0 (r/r_s)^{-\gamma} (1+r/r_s)^{-3+\gamma}$$

with gamma = 1.24, rs = 28.1 kpc, and rho0 = 3.5E-3 Msun/pc^3.

This profile never goes to zero, so it is hard to characterize how "big" it is, but one way that is often used is to ask at what radius does the density drop off to 200 times the average density of the universe. For this profile, this is atound 300 kpc, so about 10 times the size of the Milky Way galaxy. Within this radius, this profile has a total mass of about 2E12 Msun, so it dominates the mass of the galaxy. However, at smaller radii, the ordinary matter dominates. If we look at the radius of the sun (r = ~8 kpc), then the dark matter density is about .01 Msun/pc^3. We can then ask how much dark matter is, say, inside Saturn's orbit, and the result is about 1E-18 Msun or about 7E15 kg. This is the mass of a small asteroid, and is completely negligible compared to the mass of the sun and planets. Does this answer your questions?

exmarine and Lapidus
Yes, that answers my question, thanks!!

Btw, does anybody know a great review/ overview article (or a book or sections of a book) about dark matter? One that is not complete layman but not complete specialist either.

thanks!!

Btw, does anybody know a great review/ overview article (or a book or sections of a book) about dark matter? One that is not complete layman but not complete specialist either.

thanks!!

my signature contains numerous article that have sections covering dark matter. Most articles directly related to DM are related to distributions, properties etc of specific proposals and models. the misconceptions section on the http://cosmology101.wikidot.com/main signature link has one decent non technical article with a dark matter section. The articles on the site are primarily geared to helping teach modern cosmology. In particular the FLRW metrics etc. There are some textbook style articles on cosmology that include DM modelling.

http://arxiv.org/abs/1304.4446 :"What we have leaned from Observational Cosmology." -A handy write up on observational cosmology in accordance with the LambdaCDM model

you can also browse www.arxiv.com however keep in mind what I stated above, concerning the numerous alternate proposals.

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