Helical B-Fields in AGN Jets

Research done in the Active Galactic Nuclei and Radio Astronomy group at UCC suggests that many of the observed jet B-field structures may correspond to instrinsic, possible helical, B-Fields associated with the jets themselves. Helical jet B-Fields could come about in a natural way due to the combination of the rotation of the central black hole and accreation disk and the jet outflow.

One key observational signature for helical jet B-Fields is connected to the phenomenon of Faraday rotation: a rotation of the plane of polarization that occurs when a polarized electromagnetic wave passes through a region with free electrons and magnetic field. The rotation comes about due to the different propogation velocities of the right-circularly polarized and the left-circularly polarized components of the wave in the plasma.

The amount of rotation is determined by the density of free electrons and the line of sight component of the B-Field in the plasma, and is proportional to the observing wavelength squared. The sign of the Faraday rotation coincides with the sign of the line-of-sight B-field.

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