Sketch of the jet-launching region. The mm VLBI image (bottom panel) resolves structures larger than ~100 to 400 Schwarzschild radii (R_S) around the central supermassive black hole. In the innermost region, both jets have extremely large opening angles of >60°. The regions at which the two jets become optically thick, usually referred to as the two jet cores (dashed ellipses in middle part), are located at even smaller scales (< 100R_S). The magnetic field (top panel) has a toroidal configuration B ∝ r^-1 (solid line). Near the black hole, a poloidal magnetic field may start to dominate (dashed lines). The asterisk and triangle show the measured magnetic field from synchrotron cooling, using the most conservative and the lowest possible estimate of the size of the central region, respectively. From the former the toroidal field out to 1pc and the poloidal field down to 1 R_S are extrapolated, while from the latter only the poloidal field down to 1 R_S is extrapolated. The thick line in the middle of the upper panel indicates the allowed range for the magnetic field at 1 R_S. The downward arrow and square indicate the upper limit from SSA and core-shift measurements, respectively.