Discovery of minute-scale polarization angle rotation in a supermassive black hole jet

Relativistic jets from supermassive black holes aimed toward our line of sight, known as blazars, have puzzled astronomers for decades. Their fast jets and preferential alignment create a fog of relativistic effects that obscures the jets' true properties. Optical polarimetry, which traces the uniformity, direction, and evolution of the magnetic field in these jets, has revealed a phenomenon unique to blazars: coherent magnetic-field changes that appear as rotations of the polarization angle (Ψ). The origin of these rotations has been debated for decades, with several models proposed to explain them.

Using optical polarization observations combined with radio very long baseline interferometry (VLBI), the researchers detected an extremely fast, minute time-scale rotation of the polarization angle of about 136° over roughly 80 minutes. This is the fastest known such rotation by almost an order of magnitude.

The combined optical and radio data allow the team to reject different models of particle acceleration and strongly point instead to relativistic effects and the interaction of standing and moving shock waves as the origin of the extreme polarization variations in jets.