A question relating to expansion rate of the Universe

[Naty1]

Answer is still the same as when posted in #25.

edit; Maybe I should say that's about as much as we think we know...
there seems to be a lot more we don't know than we know..."Do you have a good link for this description of DM?"

not so much...search these forums, and Wikipedia has a good outline under DARK MATTER...

and I think also discusses MACHOS and WIMPS...

and I see Drakkith has posted links to hot,warm, cold dark matter...

lots of candidates, lots of questions, not so many detailed answers yet.

 

[Drakkith]

What stops DM from accumulating inside the rims and possibly near the centers of galaxies or is this unknown?

The issue is that DM can't interact through anything other than gravity. What happens is that DM follows an orbit around our galaxy just like everything else. In order for it to fall in towards the center of our galaxy and stay it must give up energy, otherwise it just swings back around all the way out to the halo region again. (or doesn't fall in at all)

When you have a dust cloud that is collapsing under its own gravity, the particles get rid of energy by colliding with each other and giving off EM radiation. This allows it to collapse into dense regions and eventually form stars, planets, etc.

But dark matter can't do this. It simply passes through itself without absorbing or giving off any energy. So it can't collapse into dense regions very easily, if at all.