论文标题
原始磁盘形成期间的谷物生长
Grain Growth During Protostellar Disk Formation
论文作者
论文摘要
最近的观察结果表明,嵌入的原始磁盘中可能存在mm/cm大小的晶粒。在恒星形成的最早阶段,这么大的晶粒如何从微米大小(或更少)中生长。在这项研究中,我们采用二维(2D轴对称)辐射流体动力和谷物生长模拟的第一步,将原始环境中的晶粒生长建模。我们表明,可以通过“末端速度近似”来大大简化晶粒生长计算,其中灰尘漂移速度相对于气体与停止时间成正比,这与晶粒尺寸成正比。我们发现,在深层嵌入的0类相的粒度上,仅依赖大小依赖性末端速度的晶粒碰撞太慢,无法将最初微小晶粒的很大一部分转换为mm/cm尺寸。当晶粒谷物碰撞速度提高4倍时,可以实现大量谷物的生长。磁盘中间平面上方和下方的尘埃生长使谷物可以更快地向中平面沉降,从而增加了局部灰尘与气体的比率,这反过来又加快了那里的进一步增长。尽管湍流是值得进一步探索的强大可能性,但如何实现这种需要的增强。
Recent observations indicate that mm/cm-sized grains may exist in the embedded protostellar disks. How such large grains grow from the micron size (or less) in the earliest phase of star formation remains relatively unexplored. In this study we take a first step to model the grain growth in the protostellar environment, using two-dimensional (2D axisymmetric) radiation hydrodynamic and grain growth simulations. We show that the grain growth calculations can be greatly simplified by the "terminal velocity approximation", where the dust drift velocity relative to the gas is proportional to its stopping time, which is proportional to the grain size. We find that the grain-grain collision from size-dependent terminal velocity alone is too slow to convert a significant fraction of the initially micron-sized grains into mm/cm sizes during the deeply embedded Class 0 phase. Substantial grain growth is achieved when the grain-grain collision speed is enhanced by a factor of 4. The dust growth above and below the disk midplane enables the grains to settle faster towards the midplane, which increases the local dust-to-gas ratio, which, in turn, speeds up further growth there. How this needed enhancement can be achieved is unclear, although turbulence is a strong possibility that deserves further exploration.