The Winding Dilemma

The Winding Dilemma
The rotation curve of the disk stars in our Galaxy indicates that most of them have the same linear (straight-line) speed. Those farther from the center take longer to
go around because they have a greater distance to travel at the same speed than stars closer to the center of the Galaxy, which orbit in smaller circles. All four dots
in these drawings have circular orbits at the same linear speed. Think of them as (a) a few stars initially in a straight line. As time goes on, the outer stars are left
behind, creating (b-d) a spiral shape that becomes more and more tightly wound. Such tightening is not observed in our Galaxy or in other galaxies.