Dynamics of the galactic bulge‐bar

Abstract

The non‐circular velocities of gas in the inner few degrees of our Galaxy would arise naturally if the Milky Way had a small bar at its center. Recent studies suggest that this bar is more rapidly rotating than had been previously suggested; corotation probably lies near R=2.4 kpc. The circular speed associated with the Galaxy’s monopole component must rise as vc∼R1/8 in the inner kiloparsec or so. It seems likely that the bar is the peanut‐shaped object seen by COBE, and formed by spontaneous thickening of a bar‐unstable disk. The lop‐sidedness of the distribution of molecular gas at ‖l‖≲2° suggests that the gas flow at the Center is unsteady. This unsteadiness may be an important clue to the correct technique for simulating the large‐scale dynamics of the interstellar medium, which displays a wealth of unresolvable structure.