原行星盘中固体颗粒的凝聚、碎裂和径向运动
Coagulation, fragmentation and radial motion of solid particles in protoplanetary disks
摘要：
在原行星盘中，固体颗粒向米级尺寸的增长必须克服至少两个障碍，即由于径向漂移和由于破坏性碰撞造成的颗粒破碎而导致的物质快速损失。在本文中，我们提出了越来越多的现实物理涉及的数值模拟的结果。一步一步，我们包括各种效果，如粒子生长，径向/垂直粒子运动和尘埃粒子破碎在我们的模拟。我们表明，初始的灰尘与气体的比例是必不可少的颗粒，以克服径向漂移障碍。如果这个值与星际介质的标准值相比增加2倍，那么在1万年内可以在小于2天文单位的内盘中形成公里大小的天体。然而，我们发现固体颗粒通过碰撞破碎而被破坏。只有在破碎所需的不切实际的高阈值速度（>30米/秒）下，颗粒才能在低湍流盘中生长到更大的尺寸。我们还发现，不到5%的小尘埃颗粒留在磁盘后，1万年由于径向漂移，无论是否包括在模拟中的碎片或没有。在本文中，我们还提出了相当大的改进，现有的算法的灰尘颗粒凝聚，加快了凝聚方案的1万倍。
英文摘要：
The growth of solid particles towards meter sizes in protoplanetary disks has to circumvent at least two hurdles, namely the rapid loss of material due to radial drift and particle fragmentation due to destructive collisions. In this paper, we present the results of numerical simulations with more and more realistic physics involved. Step by step, we include various effects, such as particle growth, radial/vertical particle motion and dust particle fragmentation in our simulations. We demonstrate that the initial dust-to-gas ratio is essential for the particles to overcome the radial drift barrier. If this value is increased by a factor of 2 compared with the canonical value for the interstellar medium, km-sized bodies can form in the inner disk <2 AU within 10 thousand years. However, we find that solid particles get destroyed through collisional fragmentation. Only with the unrealistically high-threshold velocities needed for fragmentation to occur (>30 m/s), particles are able to grow to larger sizes in low turbulent disks. We also find that less than 5% of the small dust grains remain in the disk after 1 Myrs due to radial drift, no matter whether fragmentation is included in the simulations or not. In this paper, we also present considerable improvements to existing algorithms for dust-particle coagulation, which speed up the coagulation scheme by a factor of 10 thousand.
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