A bathtub model for the star-forming interstellar medium
The bathtub model of the star forming interstellar medium (ISM) is based on the powerful constraint that mass has to be conserved when gas flows through its various thermal and density phases, ending up eventually in a young star or being blown away by stellar feedback. It predicts that the star formation rate of a molecular cloud is not determined by the cloud's mass or its internal collapse timescale, but rather by the accretion rate of new gas. For the most simple case of a constant accretion flow an equilibrium state is reached quickly where the star formation rate equals the accretion rate and where the dense gas mass is constant and independent of time. The mass of the young star cluster, on the other hand, increases linearly with time.
I will apply the bathtub model to the Milky Way disk, regulated by stellar feedback and self-gravity. It provides a natural explanation for fascinating
scaling relations observed within Toomre cells that correlate physical parameters of the filamentary molecular web over 6 orders of magnitudes in mass.