Dark nebulae -- examples of both
On close examination, there appear to be both kinds of dark nebulae here: the dust that obscures what is behind it and the matter that prevents other matter from occupying the same space. The obscuring kind has irregular edges, thins out. The solid kind has distinct curved boundaries, often lined with small stars, and appears as a uniformly-dark sphere or ellipse. Both are distinguishable in this object.
"small sphere":(29x29@202,519)"ellipsoid edged with stars":(49x42@313,23)"sphere with stars":(29x29@202,102)"irregular edges??":(81x47@205,453)"ellipsoid lined with stars":(34x36@75,283)"sphere lined with stars, surrounded by irregular edges":(29x29@210,552)