Helical density waves in flat galaxies-moving solitons
Mikhailovskii A.B., Petviashvili V.I. , Fridman A.M.
It is shown that solitons of two types, supersonic and subsonic, can propagate in a rotating gravitating disk. The supersonic solitons are capable of propagating only in the case of a weak Jeans instability of the disk. The subsonic solitons can propagate only in a stable (as defined by Jeans) disk.