Magnetic flux density from the relative circular motion of stars and partially ionized gas in the galaxy mid-plane vicinity

Observations suggest a slower stellar rotation relative to gas rotation in the outer part of the Milky Way Galaxy. This difference could be attributed to an interaction with the interstellar magnetic field. In a simple model, fields of order $10\mu G$ are then required, consistently with the observed values. This coincidence suggests a tool for estimating magnetic fields in spiral galaxies. A north–south asymmetry in the rotation of gas in the Galaxy could be of magnetic origin too.