Dr Charles Bruce postulated in 1968 that spiral galaxy arms are huge lightning strikes. Recent work in radio astronomy bears him out.
Flows of electric current in these flat looped galactic circuits involves the movement of ions, Van der Graaf fashion, as indicated here by the short black lines. The gradual build up of opposite charges at the remote ends of the galaxy continues until electrical breakdown causes another lightning strike. Then charging begins again.
This charge/discharge periodicity, the basis of many earthly electronic clocks and timers, provides a cogent and overdue explanation for the many periodic objects in space: from pulsars to sunspot cycling. See later.
Flatness and spirality in celestial bodies is fundamental to the explanation of their generation of electricity and their shape.