The numerical simulation of external gas spirals

We consider the physical mechanism that can explain the nature of the observed spiral patterns on the periphery of galaxies outside the optical radius, according to HI and ultraviolet range. The generator of spiral structures in the gas outside the stellar disk can be nonaxisymmetric halo. The numerical gas-dynamic experiments have shown that nonaxisymmetric dark halo may be an efficient generator of spiral structures in the gas outside the stellar disk.