  The origin of the "Changing-look" (CL) phenomenon in supermassive black holes
(SMBHs) remains an open issue. This study aims to shed light on this phenomenon
by focusing on a sample that encompasses all known repeating CL active galactic
nuclei (AGNs). Through the identification of a characteristic time scale for
the CL phenomenon, it was observed that larger SMBHs possess shorter
characteristic timescales, while smaller SMBHs exhibit longer timescales. These
findings reveal a significant contrast to the traditional AGN variability that
has been adequately explained by the AGN's disk instability model. This stark
discrepancy highlights a distinct origin of the CL phenomenon, distinguishing
it from traditional AGN variability. By properly predicting the characteristic
time scale and its dependence on SMBH mass, we propose that the CL phenomenon
is likely a result of a variation in accretion rate caused by a sudden change
in the supply of circumnuclear gas during the transition between active and
passive SMBH fueling stages.
