An important input factor to the model discussed so far is the power of the jet  (here we mainly considered the magnetic power L_B). A nice feature of the model is that it can be scaled over many orders of magnitude by just changing the power input of the jet. This is presumably done by a parallel change in the accretion disk power. Doing so would change the power of the radio core but would not change its spectral shape only the turnover frequency might change. To a radio observer the jet would always appear as a flat-spectrum core. This may be the reason why radio jets are expected for almost every type of active black hole: from supermassive to stellar, from powerful to faint.

Indeed, compact, flat spectrum radio cores have been found in sources like quasars, Seyfert galaxies, low-luminosity AGNs and LINERs, as well as in X-ray binaries, confirming that the physics we have discussed for Sgr A^* is fairly universal. The exact nature of the cores and the emission of these other engines is not the main focus of the book and further discussion of this point can be found in Falcke (2001). However, the general point one can make is that as the accretion power and the disk luminosity decreases, one expects to see fainter radio cores. If there is a range in accretion rates throughout the universe, we also expect a range of core luminosities. Where Sgr A^* like radio cores of various different types are shown for a range of luminosities. In such a plot, Sgr A^* would come in at the bottom left of the distribution for an accretion rate of 10⁻⁸ M_ּ yr⁻¹ (as indicated by the upper black dot with a horizontal error bar; the other point indicates the estimated position for M31^* the core in the Andromeda galaxy). However, since the accretion disk in Sgr A^* is so faint and the accretion rate so uncertain, we cannot actually derive an accretion disk luminosity or accretion power and this should only be considered as a general guideline. The bottom line is, however, that Sgr A^* with its radio properties is not alone in the universe but is at the bottom end of the activity scale seen from supermassive black holes.