The effects of a compressive velocity pulse on a collapsing turbulent clump

Abstract

High‐resolution hydrodynamical simulations are presented to follow the gravitational collapse of a uniform turbulent clump, upon which a purely radial compressive velocity pulse is activated in the midst of the evolution of the clump, when its turbulent state has been fully developed. The shape of the velocity pulse is determined basically by two free parameters: the velocity V0 and the initial radial position r0. In the present paper, models are considered in which the velocity V0 takes the values 2, 5, 10, 20, and 50 times the speed of sound of the clump c0, while r0 is fixed for all the models. The collapse of the model with 2 c0 goes faster as a consequence of the velocity pulse, while the cluster formed in the central region of the isolated clump mainly stays the same. In the models with greater velocity V0, the evolution of the isolated clump has significantly changed, so a dense shell of gas forms around r0 and moves radially inward. The radial profile of the density and velocity and the mass contained in the dense shell of gas are calculated, and it is found that (a) the higher the velocity V0, the less mass is contained in the shell, and (b) there is a critical velocity of the pulse, around 10 c0, such that, for shock models with a lower velocity, there will be a well‐defined dense central region in the shocked clump surrounded by the shell.

Comparing binary systems from rotating parent gas structures with different total masses

“…Despite of this, when we calculated the α f and β f values we observe that some binary fragments do show a clear tendency to virialize, as it can be appreciated in Fig.31. We emphasize that a similar conclusion can be drawn from the calculation of Arreaga et al (2008), where plots of the α f and β f time evolution were also presented. On the contrary, for the central primaries, we do not observe any trend to approach the virial line; see Fig.33.…”

“…This mass perturbation scheme was successfully applied in many papers on collapse; see for instance Arreaga et al (2007), Arreaga et al (2008), Arreaga and Klapp (2010), and notably Springel (2005), when the Gadget2 code was proven, among other tests, with the calculation of the isothermal collapse, where the unequal mass particles method was validated. et al (1997) demonstrated the need of fulfill appropriate spatial resolution requirements in order to avoid the occurrence of artificial fragmentation in a collapse simulation.…”