  Magnetic fields in galaxy halos are in general very difficult to observe.
Most recently, the CHANG-ES collaboration (Continuum HAlos in Nearby Galaxies -
an EVLA Survey) investigated in detail the radio halos of 35 nearby edge-on
spiral galaxies and detected large scale magnetic fields in 16 of them. We used
the CHANG-ES radio polarization data to create Rotation Measure (RM) maps for
all galaxies in the sample and stack them with the aim to amplify any
underlying universal toroidal magnetic field pattern in the halo above and
below the disk of the galaxy. We discovered a large-scale magnetic field in the
central region of the stacked galaxy profile, attributable to an axial electric
current that universally outflows from the center both above and below the
plane of the disk. A similar symmetry-breaking has also been observed in
astrophysical jets but never before in galaxy halos. This is an indication that
galaxy halo magnetic fields are probably not generated by pure ideal
magnetohydrodynamic (MHD) processes in the central regions of galaxies. One
such promising physical mechanism is the Cosmic Battery operating in the
innermost accretion disk around the central supermassive black hole. We
anticipate that our discovery will stimulate a more general discussion on the
origin of astrophysical magnetic fields.
