Universal transition diagram from dormant to actively accreting
  supermassive black holes
  The vast majority of supermassive black holes (SMBHs) in the local universe
exhibit levels of activity much lower than those expected from gas supplying
rates onto the galactic nuclei, and only a small fraction of silent SMBHs can
turn into active galactic nuclei. Revisiting observational data of very nearby
SMBHs whose gravitational spheres of influence are spatially reached by the
Chandra X-ray satellite, we find that the level of BH activity drastically
increases from the quiescent phase when the inflow rate outside of the BH
influence radius is higher than 0.1% of the Eddington accretion rate. We also
show that the relation between the nuclear luminosity and gas accretion rate
from the BH influence radius measured from X-ray observations is well described
by the universal state transition of accreting SMBHs, as predicted by recent
hydrodynamical simulations with radiative cooling and BH feedback. After the
state transition, young massive stars should form naturally in the nucleus, as
observed in the case of the nearest SMBH, Sagittarius A$^\ast$, which is
currently quiescent but was recently active.
