Other effects, such as light scattering from cosmic dust and the synchrotron radiation generated by electrons moving around galactic magnetic fields within our own galaxy, can also produce these polarisation twists. (faith.org.uk)
We propose that the cycle may be caused by modulation of cosmic ray (CR) flux by the Solar system vertical oscillation (64 My period) in the galaxy, the galactic north - south anisotropy of CR production in the galactic halo / wind / termination shock (due to the galactic motion toward the Virgo cluster), and the shielding by galactic magnetic fields. (realclimate.org)
But because the particles are electrically charged, they interact with galactic magnetic fields, causing them to wander in their journey to Earth. (sciencedaily.com)