Opening again the debate: the transient nature of the circumnuclear disk

Despite many investigations, the physical characteristics of the molecular gas in the Galactic center circumnuclear disk (CND) remain a topic of debate. Its mass is highly uncertain, between 10⁴ (from dust) and 10^5-6 M_⊙ (derived from gas tracers), and depending on the probe, density estimates for the dense clumps are 10^5-8 cm_-3 and gas temperatures run from 50 to a few hundred K. The range of physical parameters leaves open many questions about the nature and fate of the CND. Using several ground-based observatories, together with Herschel and SOFIA, we have studied the physical conditions of the dense clumps using CO, HCN and HCO⁺, finding that most of them are transient. Their densities are not large enough for them to be gravitationally bound in the tidal field in the center of our Galaxy.