Triggered star formation by shocks
  Star formation can be triggered by compression from shock waves. In this
study, we investigated the interaction of hydrodynamic shocks with Bonnor-Ebert
spheres using 3D hydrodynamical simulations with self-gravity. Our simulations
indicated that the cloud evolution primarily depends on two parameters: the
shock speed and initial cloud radius. The stronger shock can compress the cloud
more efficiently, and when the central region becomes gravitationally unstable,
a shock triggers the cloud contraction. However, if it is excessively strong,
it shreds the cloud more violently and the cloud is destroyed. From simple
theoretical considerations, we derived the condition of triggered gravitational
collapse, which agreed with the simulation results. Introducing sink particles,
we followed the further evolution after star formation. Since stronger shocks
tend to shred the cloud material more efficiently, the stronger the shock is,
the smaller the final (asymptotic) masses of the stars formed (i.e., sink
particles) become. In addition, the shock accelerates the cloud, promoting
mixing of shock-accelerated interstellar medium gas. As a result, the
separation between the sink particles and the shocked cloud center and their
relative speed increase over time. We also investigated the effect of cloud
turbulence on shock-cloud interaction. We observed that the cloud turbulence
prevents rapid cloud contraction; thus, the turbulent cloud is destroyed more
rapidly than the thermally-supported cloud. Therefore, the masses of stars
formed become smaller. Our simulations can provide a general guide to the
evolutionary process of dense cores and Bok globules impacted by shocks.
