  We report here on a calculation of thermalization time-scale of the two
temperature advection dominated accretion flow (ADAF) model. It is established
that time required to equalize the electron and ion temperatures via
electron-ion collisions in the ADAF with plausible physical parameters greatly
exceeds age of the Universe, which corroborates validity one of the crucial
assumptions of the ADAF model, namely the existence of a hot two temperature
plasma. This work is motivated by the recent success (Mahadevan 1998a,b) of
ADAF model in explaining the emitted spectrum of Sgr A*.
