Of galactic magnetism
The origin of magnetic fields associated with galaxies is still a matter of debate. One theory attributes it to a dynamo-like mechanism in rhe galaxies, while the other contends that the dynamo is long dead and the magnetic field is constant. Both the theories are based on magneto-hydrodynamics which says that magnetic field is frozen into the interstellar gas.
Researchers have recently reported the existence of magnetic spiral arms in the galaxy NGC6946, This finding could have major implications on the understanding of the mechanism responsible for the magnetic field, since it is difficult to explain a pure magnetohydrodynamic origin of such an effect.