星形成
To inquire into the origin and fate of a galaxy's halo gas is to inquire into the evolution of said galaxy. HVCs and IVCs are significant features of a spiral galaxy's structure. These clouds are of primary importance when considering a galaxy's Star formation rate (SFR). The Milky Way has approximately 5 billion solar masses of star forming material within its disk and a SFR of 1–3 formula_1 yr−1. Models for galactic chemical evolution find that at least half of this amount must be continuously accreted, low-metallicity material to describe the current, observable structure. Without this accretion, the SFRs indicate that the current star formation material will only last for another few gigayears (Gyr) at most.