Mass Supply to Galactic Center due to Nested Bars in the Galaxy
  We investigate rapid mass supply process by nested bars in the Galaxy by numerical simulation. We simulate gas flow in the whole galaxy disk with nested bars, which are the outer bar and the inner bar, especially with highly spatial resolution in the galactic central region. We assume two cases of inner bar size which are a smaller one and a larger one than the radius of the 200 pc gas ring which is corresponds to the Central Molecular Zone. From our numerical results, in the large size bar cases, the inner bars with large elongation induce sufficient mass inflow and destroy the 200 pc gas ring. On the other hand, in the small size bar cases, the inner bars with large elongation induce large mass inflow and do not destroy the 200 pc gas ring. This mass inflow is caused by straight shocks excited by the inner bar. In this case, nuclear gas disks of ~ 15 pc radius are formed. The nuclear gas disks are self-gravitationally unstable and we expect formation of compact star clusters under strong tidal force in the nuclear gas disks. We discuss evolution of the nuclear gas disk. 
Daisuke Namekata, Asao Habe, Hidenori Matsui, Takayuki R. Saitoh