Q&A: Dark Matter

Q:
George Gamow, in his book "The Creation of the universe," explained why the galaxies rotate as a solid body as actually being a "dipping elliptical trajectory" of the stars. So why are we looking for the missing matter when the "falling" of stars through galactic gas is more reasonable?

A:
I think Gamow was referring to the inner regions of galaxy. The outer regions don't rotate as a solid body, which has a constant angular velocity of rotation. Rather they have a constant linear velocity of rotation. The angular velocity declines inversely as the radius.