Magnetic Monopoles if they exist would interact with the galactic magnetic field. The galactic magnetic field is produced by the differential rotation of ionized gases on a galactic scale. These fields act as monopole accelerators and help to eject monopoles out of the galaxies. Monopols whould also depleat the galactic magnetic field, This puts a limit to how many monopoles can be floating out in the galaxiy. To many would eliminate the galactic magnetic feild.
