  Enigmatic spiral structure of many galaxies and its huge orbital momentum
originated due to the capture of lightweight bare black hole by gravity of
heavy primordial gas cloud at large impact parameter. The rotating of black
hole caused the formation of accretion disc from the cloud and the transfer of
orbital momentum to the disc, while during the fall to the center of mass, the
spiral trace of black hole in the disc did create the spiral front line of
sound waves in the gas, that further evolved into the stellar spiral arms. This
mechanism opens the way to study features of spiral galaxy formation, say, an
influence and a significance of dark matter in this process.
