How can galxies and dwarf galaxies be made of regular AND dark matter?

[fellupahill]

If dark matter is actually there and not just some flaw in our understanding or mathematics then how can galaxies be made of both and not just one or the other. If dark matter doesn't interact with anything else like light then how can a dwarf galaxy be made of "mostly dark matter"?I know its probably just a misunderstanding of mine, but right now it really seems like dark matter is a scape goat. Do a lot of experts share this hypothesis?
What are some other reasons why physicists believe dark matter is there, other than its gravitational effects on the movement of galaxies? Or is that pretty much it? (I understand this is a big deal, ha) and finally, what are the leading theories that explain dark matter and which do you support?

[Drakkith]

Both matter and dark matter interact through gravity, but neither interact with each other in any other way. So dark matter is simply there in space like normal matter is.

[fellupahill]

but proportional enough to form almost perfect circles around galaxies? wouldnt they just form their own random clumps? I mean they are stronger? Does that mean its strong enough so almost all matter is inside dark matter? But not strong enough to cause any negative effects? or whatever the technical term in physics is for "negative effects" is.

Its obvious that Im missing something in my understanding. Elighten? :)

[yenchin]

It is thought that in the early universe small perturbation of dark matter density causes clumps to eventually form, and this is the scaffolds that visible matter adheres to later on. See e.g. this (http://www.youtube.com/watch?v=Cdoj-sHF370).

Here are some good readings about properties of dark matter and why most experts think they are needed [instead of say, modified gravity]. A quick answer is dark matter explanation fits well not just for galaxies rotation curve, galaxy cluster, gravitational lensing, but also the cosmic microwave background data.

What is Dark Matter? (http://scienceblogs.com/startswithabang/2009/10/what_is_dark_matter.php)

The Status of Dark Matter (http://scienceblogs.com/startswithabang/2011/10/the_status_of_dark_matter.php)

A New Test of Dark Matter vs. Modified Gravity (http://scienceblogs.com/startswithabang/2011/10/a_new_test_of_dark_matter_vs_m.php)

Dark Matter: Just Fine, Thanks. (http://blogs.discovermagazine.com/cosmicvariance/2011/02/26/dark-matter-just-fine-thanks/)

[fellupahill]

That post clarified things perfectly for me. Is this uniformly believed? That dark matter was essential for galaxy formation? It makes perfect sense.

In science, even when you're convinced that you know the right answer, you keep testing your understanding in new ways.
-ethan siegel I like that perfect quote.

edit
perfect. perfection. post perfection. infinite perfection. lol