This work presents a conceptual reinterpretation of the observed flattening of galactic rotation curves, without invoking dark matter or MOND-based modifications of gravity. By treating spiral arms as density waves, stars moving within these high-density patterns experience an apparent acceleration, which remains roughly constant across the outer regions of galaxies. This mechanism naturally explains the flat rotation curves of stars at large galactocentric distances. The approach builds upon the pioneering work of Chandrasekhar, Lin, and Shu on density wave theory, providing a framework to understand galactic dynamics from first principles. This conceptual model highlights how wave-induced motion can produce observational effects similar to those attributed to hypothetical gravitational modifications, while remaining grounded in observable galactic structure.
Akihito Sugawara (Tue,) studied this question.