Constraints on the radio-loud/radio-quiet dichotomy from the Fundamental Plane

The Fundamental Plane for black hole activity constitutes a tight correlation between jet power, X-ray luminosity, and black hole mass. Under the assumption that a Blandford-Znajek-type mechanism, which relies on black hole spin, contributes non-negligibly to jet production, the sufficiently small scatter in the Fundamental Plane shows that black hole spin differences of |Delta a| similar to 1 are not typical among the active galactic nuclei population. If - as it seems - radio-loud and radio-quiet objects are both faithful to the Fundamental Plane, models of black hole accretion in which the radio-loud/radio-quiet dichotomy is based on a spin dichotomy of a similar to 1/a similar to 0, respectively, are difficult to reconcile with the observations. We show how recent theoretical work based on differences in accretion flow orientation between retrograde and prograde, accommodates a small scatter in the Fundamental Plane for objects that do have non-negligible differences in black hole spin values. We also show that the dichotomy in spin between the most radio loud and the most radio quiet involves |Delta a| a parts per thousand 0. And, finally, we show how the picture that produces compatibility with the Fundamental Plane, also allows one to interpret other otherwise puzzling observations of jets across the mass scale including (1) the recently observed inverse relation between radio and X-rays at higher Eddington ratios in both black hole X-ray binaries as well as active galactic nuclei and (2) the apparent contradiction between jet power and black hole spin observed in X-ray hard and transitory burst states in X-ray binaries.