Gas density, stability, and starbursts near the inner lindblad resonance of the milky way

A key project of the Antarctic Submillimeter Telescope and Remote Observatory reported by Martin et al. is the mapping of CO J = 4 → 3 and J = 7 → 6 emission from the inner Milky Way, allowing determination of gas density and temperature. Galactic center gas that Binney et al. identify as being on x₂ orbits has a density near 10^3.5 cm ³, which renders it only marginally stable against gravitational coagulation into a few giant molecular clouds, as discussed by Elmegreen. This suggests a relaxation oscillator mechanism for starbursts in the Milky Way, whereby inflowing gas accumulates in a ring at 150 pc radius until the critical density is reached and the resulting instability leads to the sudden formation of giant clouds and the deposition of 4 × 10⁷ M _⊙ of gas onto the Galactic center. Depending on the accretion rate near the inner Lindblad resonance, this cycle will repeat with a timescale of order 20 Myr.