Question Re galactic Spiral arm rotation...
Perhaps one of you more up-to-date astronomers can answer this for me...
The spiral arms of galaxies have been demonstrated to be formed by density waves in the interstellar medium and are marked by regions of young, blue Population I stars condensing along the wave front. It follows that the arms are not necessarily unwinding in the direction of galactic rotation. Or does it? Has anyone published anywhere either theory or observation supporting whether spiral galaxies are indeed rotating in the direction their spiral arms indicate they are? Rotation and spirality may well be intimately connected, but the interaction may be more subtle than intuition would lead you to expect. In a related question, do ellipticals rotate? Thanks.