Why do galaxies spin (is there a black hole in the center)?

The electric motor effect says if a current flows through a magnetic field the conductor will move at right angles to both the current and the field.

Any time a charged particle moves, that is an electric current. If there is a magnetic field, the particle will move in a circular path. Go to youtube.com and search for "faraday disk" to see a demonstration.

Any bit of light can knock an electron off an atom, so the normal state of most of the universe, over 90%, is a collection of charged particles, magnetic fields, and rotating clouds of material. The black hole is entirely imaginary, only needed because astronomers don't like to think about electric charges.