  Relativistic outflows (mainly observed in the radio) are a characteristic
feature of both Galactic stellar mass black holes and supermassive black holes
(SMBHs). Simultaneous radio and X-ray observations of Galactic sources have
shown that the outflow is strong at low accretion rates, but it weakens
dramatically or disappears completely at high accretion rates, manifesting
structural changes in the accretion flow. It is reasonable to assume that SMBHs
follow the same trend. For low luminosity SMBHs in nearby elliptical galaxies
and clusters, recent observations strongly suggest that the outflows play the
central role in keeping the gas hot (mechanical feedback). If the outflow is
quenched in SMBHs at high accretion rates similarly to the behavior of galactic
sources, then the straightforward consequence is a relatively weak feedback of
rapidly accreting SMBHs. We argue that elliptical galaxies and their central
engines should then evolve through two stages. Early on, the central SMBH
rapidly grows by accreting cooling gas at a near-Eddington rate with high
radiative efficiency but with weak feedback on the infalling gas. This stage
terminates when the black hole has grown to a sufficiently large mass that its
feedback (radiative and/or mechanical), despite the low gas heating efficiency,
is able to suppress gas cooling. After that the system switches to a stable
state corresponding to passively evolving ellipticals, when the accretion rate
and radiative efficiency are very low, but the gas heating efficiency is high
and energy input from the relativistic outflow keeps the gas hot.
