Zooming into the heart of a radio galaxy

The formation of relativistic jets in active galaxies is a poorly understood physical process. Providing observational constraints for theoretical models is a crucial but challenging task, since it requires the imaging of emission regions in the immediate proximity of the black hole. We have observed the prototype radio galaxy Cygnus A through very-long-baseline interferometry at millimeter wavelengths, and obtained a sharp view of the jet base. Our analysis of the jet kinematic properties and internal structure suggests that the jet of Cygnus A is a disk wind accelerated by magnetic fields.