Dust Processing during the Gravitational Collapse of Particle Heaps

在这个项目中，我们将研究在星子前体（0.1cm - 1m）的引力坍缩过程中形成星子的物质的命运。在早期太阳系中，形成千米大小的星子的一个非常有吸引力的方法是由相对较小的冰和尘埃物体组成的云的“引力湍流碎片”。例如，在非湍流中，粒子的层流盘沉降导致的是由开尔文-亥姆霍兹不稳定性驱动的湍流，而不是密度足以导致引力坍缩的粒子层（戈德里奇-沃德不稳定性）。最近对粉尘团聚体的混凝效率的研究表明，厘米大小的粉尘团聚体可以迅速形成。然而，任何进一步的增长似乎都受到反弹或破碎障碍的抑制。因此，Johansen等人（2006a, 2007）提出了一种混合方案，在这种方案中，湍流浓度取决于盘中毫米到米大小的冰和尘埃物质的位置，导致足够大的密度，其中自重力主导气体阻力和恒星的潮汐力，因此一堆物质在自身重量的作用下自发地坍缩成许多公里大小的行星。在这个项目中，我们的目标是研究重力破碎阶段碰撞的影响。我们在这里想要解决的一个主要问题是，固体的碰撞碎片是否能阻止坍缩，从而减少或破坏由引力碎片形成星子的可能性。

In this project we will investigate the fate of the material which is building up planetesimals during the gravitational collapse of heaps of planetesimal precursors (0.1cm - 1m). A very attractive way to form the kilometre sized Planetesimals in the early solar system is the ”Gravoturbulent Fragmentation” of a cloud of relatively small icy and dusty objects. In a nonturbulent e.g. laminar disk sedimentation of particles leads rather to a Kelvin-Helmholtz instability driven turbulence than to a particle layer dense enough for gravitational collapse (Goldreich-Ward instability). Latest studies on the coagulation efficiency of dust aggregates have shown that cm-sized dust aggregates can rapidly form. However, any further growth seems to be inhibited by either the bouncing or the fragmentation barrier. Hence, Johansen et al. (2006a, 2007) came up with a hybrid scenario in which turbulent concentration of depending on the location in the disk millimetre to meter sized icy and dusty material leads to sufficiently large densities in which self gravity dominates over gas drag and the tidal forces of the star, thus a heap of material collapses spontaneously under its own weight into a many kilometre sized planetesimal. In the proposed project we aim to investigate the effect of the collisions during the gravitational fragmentation3 phase. A main question we want to address here, is whether a collisional fragmentation of the solids could stop the collapse and thus diminish or destroy the possibility to form planetesimals from gravitational fragmentation.