Dynamically triggered star formation in giant molecular clouds

Abstract

A Lagrangian, particle-based numerical method (tree code gravity plus smoothed particle hydrodynamics) was used to simulate clump-clump collisions occurring within GMCs. The collisions formed shock-compressed layers, out of which condensed approximately co-planar protostellar discs of 7-60 solar masses and 500-1000AU radius. Binary and multiple systems were the usual final state. Lower mass objects were also produced, but commonly underwent disruption or merger. Such objects occasionally survived by being ejected via a three-body slingshot event resulting from an encounter with a binary system. Varying the impact parameter, b, altered the processes by which the protostellar systems formed. At low b a single central disc formed initially, and was then spun-up by an accretion flow, causing it to produce secondaries via rotational instabilities. At mid b the shocked layer w hich formed initially broke up into fragments, and discs were then formed via fragment merger. At large b single objects formed within the compressed leading edge of each clump. These became unbound from each other as b was increased further. The effect of changing numerical factors was examined by : (i) colliding clumps which had been re-oriented before the collision (thus altering the initial particle noise), and (ii) by quadrupling the number of particles in each clump (thus increasing the resolution of the simulation). Both changes were found to affect the small-scale details of a collision, but leave the large scale morphology largely unaltered. It was concluded that clump-clump collisions provide a natural mechanism by which multiple protostellar systems may form.Comment: 15 pages, 12 low resolution figures in 50 files, accepted by MNRA

A Mapping Survey of Dense Clumps Associated With Embedded Clusters. Ii. Can Clump-Clump Collisions Induce Stellar Clusters?

“…In their simulation, the clump-clump collisions produce multiple stars from B6 to B0 stars. The spatial and kinematic properties in our results are consistent with those of Bhattal et al (1998). Their calculated β rot are 0.1-0.2 during the interaction.…”

“…While such observational evidence for cloud-cloud collision exists, the previous studies were mainly based on the spatial distribution between clouds and clusters in most cases. In the theoretical perspective, Bhattal et al (1998) simulated the phenomena of collisions of two clumps (size ∼1 pc, mass ∼100 M ⊙ , collision speed ∼1 km s −1 ) in a wide range of impact parameters. Their results show rigid-like rotations of the gas motion induced by clumpclump collision, for isothermal spheres, in the collision with a small impact parameter (the impact parameter is 0.3).…”

The minimum mass for opacity-limited fragmentation in turbulent cloud cores

“…Second (again from a theoretical perspective), the fragmentation of a layer normally proceeds via the formation of a network of filaments (e.g. Turner et al 1995;Whitworth et al 1995;Bhattal et al 1998); this is because of the well established theorem (e.g. Zeldovich 1979) which asserts that if gravitational contraction gets ahead in one dimension (due either to a greater initial perturbation, or less resistance), it tends to get further ahead.…”

MODEST-1: Integrating stellar evolution and stellar dynamics

“…With the rapid increase of computer power in recent years, more realistic calculations became possible. Whitworth et al (1995) and Bhattal et al (1998) investigated in detail the fragmentation of shocked interfaces of colliding molecular clumps into small stellar systems. Klessen et al (1998), and Klessen & Burkert (2000) studied the formation of stellar clusters from random Gaussian density fluctuation in molecular clouds.…”