What is gravity doing in star-forming regions? An observational view

Gravity plays important roles in the evolution of molecular clouds. Due to its long-range nature, its effects are not easily recognised.  We present a method to estimate the acceleration induced by large-scale gravitational field in molecular clouds based on observational data. We found that gravity plays diverse roles in different regions. It can induce collapses at the ends of filamentary structures. Quantitative investigations reveal that the pressure resulting from gravitational acceleration in the localised regions is larger than turbulence pressure. Neglecting magnetic fields, gravity can promote formation of parsec-scale dense gas at around million-year timescale. Theoretical implications for star formation and galaxy evolution will be discussed.