The Effect of Shock Wave Duration on Star Formation and the Initial Condition of Massive Cluster Formation

Stars are born in dense molecular filaments. Compression of the interstellar medium by shocks causes filament formation in molecular clouds. Observations show that a massive star cluster formation occurs where the peak of gas column density in a cloud exceeds  \(10^{23}\)  cm \(^{-2}\) . In this chapter, we show the effect of the shock-compressed layer duration on filament/star formation and how the initial conditions of massive star formation are realized by performing three-dimensional isothermal MHD simulations with gas inflow duration from the boundaries as a controlling parameter. Filaments formed behind the shock expand after the duration time for short-shock-duration models, whereas long-duration models lead to star formation by forming massive supercritical filaments. Moreover, when the shock duration is longer than two post-shock freefall times, the peak column density of the compressed layer exceeds  \(10^{23}\)  cm \(^{-2}\) , and the gravitational collapse of the layer causes the number of OB stars expected to be formed in the shock-compressed layer to reach the order of 10 (i.e., massive cluster formation).