Comment by Ekaros

You need certain density to start formation progress. Then you get more density as it drags more stuff via gravity from intergalactic void. So new stars form at edges when there is finally enough stuff pulled by gravity of whole galaxy to there for the formation to happen.

It seems that you need quite large concentrations(as in scale of whole universe average) to actually get to star formation. Otherwise stars would be uniform trough the universe.

Then again I am not astronomer.