Fair enough, it's a bit of a tangent. Thanks for the extra insight! I kinda' assumed that stars wouldn't move across a galaxy, like from one arm to another. I'll have to look into that.
Yes, stars move through the arms, and circle around the center of the galaxy. The arms actually also "move", but not in the way you would maybe expect. They are actually density waves - areas of greater density of gas & dust, similar to a traffic jam on a highway. These waves also "move" along with the gas & dust. But this wave-movement is illusory, because they are formed by these traffic jams.
The stars move through these waves (traffic jams), and in these high density areas new star formation and supernovas happens mostly (because there is more stuff to collect). The stars move through the gas & dust faster than the gas & dust themselves, because the stars are more massive and need more velocity to stay in stable orbit. The illusory movement of the waves is also slower than the stars, because the illusory waves move as slow as the dust & gas that forms them, and the stars are faster.
Apart from that, you also have dark matter which influences the rotation speed of objects based on it's distance from the galaxy center. It causes objects at the end of the spiral arms of the galaxy to rotate at the same speed as the ones close to the center, or anywhere. That is a mysterious area, and actually caused the requirement of dark matter into the equation. Because in Einstein's relativity theory, objects with same mass that are farther away from the galaxy center, need to move slower to have a stable orbit, which is the case in our solar system and other solar systems we observe. But in galaxies the case seems to be different. That is why dark matter was introduced, and makes it more complicated.
