On spiral structure formation in a galaxy with a bar-like nucleus

A new approach to the problem of the formation of galaxy spiral structures having a rotating bar-like nucleus is offered. The process of disk formation due to matter accretion onto the disk is considered in terms of the solution of the key problem on the motion of the matter element in the equatorial plane of the galaxy in the corotation resonance region. It is shown that in the vicinity of unstable libration points high-density regions are formed, which elongate with time following the separatrix shape and forming thereby spiral arms.