Spiral structure of galaxies two alternatives

At present the wave theory of the spiral structure of the galaxies includes two alternative viewpoints. Two types of spiral waves—short-wave and long-wave modes—can be excited. According to Lin and Shu (1964) the short-wave modeK is responsible for the spiral structure of the galaxies and, according to Marochniket al. (1972), the long-wave mode (K ₀). In our Galaxy theK -mode corresponds to the wave with an angular rotation velocity _p =11–13 kms^–1 kps^–1 and a radial group velocity directed from the periphery to the center. TheK ₀-mode corresponds to the wave having an angular rotation velocity _p =23 ± 3 kms^–1 kps^–1 and a radial group velocity directed from the center of the Galaxy to its periphery. The theoretical and observational evidences in favour of Marochniket al.'s (1972) model are given.