Why do some regions of our Milky Way galaxy appear dark?

Is it because there's no stars or that they're hidden by instellar gas or dus? Or is that whole black hole thing that capture all the light behind them. I'm lost...

Why do some regions of our Milky Way galaxy appear dark?

Is it because there's no stars or that they're hidden by instellar gas or dus? Or is that whole black hole thing that capture all the light behind them. I'm lost...
Hiya

I think the links below should give you all the info you need.

Milky Way - Wikipedia, the free encyclopedia (http://en.wikipedia.org/wiki/Milky_Way)
The Milky Way Galaxy (http://physics.uoregon.edu/~jimbrau/astr123/Notes/Chapter23.html)
The Milky Way Galaxy (http://home.xtra.co.nz/hosts/Wingmakers/The%20Milky%20Way%20Galaxy.html)