Recent radio VLBI observations of the complex gravitationally lensed system PKS1830-211 have thrown up some questions with regard to the processes occuring at the heart of the blazar source at a redshift of 2.51 , which is viewed almost straight down the jet axis .
This work links , by a model of a helical jet tracked by ballistically ejected plasmons from a precessing nozzle , observations on the scale of tens of microarcseconds to those on the scale of milliarcseconds .
An observed jet precession period of 1.08 years is inferred from the model , translating to an intrinsic period of 30.8 years for a source at redshift z _ { s } = 2.51 and an assumed jet bulk velocity \beta of 0.99 c .
This fits well with the picture of the active galactic nucleus hosting a binary black hole system at its centre , with the jet emitted by one member of the system , and the precession as being due to its orbital motion around its companion .