在实验室实验中，我们研究了紧凑的合奏（填充因子0.33）毫米灰尘聚集体组成的微米石英颗粒的碰撞。我们使用圆柱形聚集体、三角形聚集体、正方形聚集体和矩形聚集体。研究了等尺寸聚集体的集合以及嵌入较大聚集体的集合。典型的碰撞速度为10-20 mm $\rm s^{-1}$。高空间和时间分辨率成像明确显示，单独的碰撞导致粘附的概率高达20%。这导致聚集体的连接集群。两个聚集体之间的接触面积随着碰撞速度的增加而增加。然而，这种团簇增长只是暂时的，因为随后的聚集体和团簇的碰撞最终导致所有聚集体从团簇中分离。接触是非常脆弱的，因为在我们的实验条件下，聚集体不能进一步压缩或破碎，以提高接触稳定性。因此，系综的演化总是导致初始大小的个体聚集体的分布。这支持并扩展了早期的实验，表明在星子形成中的弹跳屏障对于形状和大小的变化是鲁棒的。
英文摘要：
In laboratory experiments, we studied collisions of ensembles of compact (filling factor 0.33) millimeter dust aggregates composed of micrometer quartz grains. We used cylindrical aggregates, triangular aggregates, square aggregates, and rectangular aggregates. Ensembles of equal size aggregates as well as ensembles with embedded larger aggregates were studied. The typical collision velocities are 10-20 mm $\rm s^{-1}$. High spatial and temporal resolution imaging unambiguously shows that individual collisions lead to sticking with a high probability of 20 percent. This leads to connected clusters of aggregates. The contact areas between two aggregates increase with collision velocity. However, this cluster growth is only temporary, as subsequent collisions of aggregates and clusters eventually lead to the detachment of all aggregates from a cluster. The contacts are very fragile as aggregates cannot be compressed further or fragment under our experimental conditions to enhance the contact stability. Therefore, the evolution of the ensemble always leads back to a distribution of individual aggregates of initial size. This supports and extends earlier experiments showing that a bouncing barrier in planetesimal formation would be robust against shape and size variations.
After 25 years of laboratory research on protoplanetary dust agglomeration, a consistent picture of the various processes that involve colliding dust aggregates has emerged. Besides sticking, bouncing and fragmentation, other effects, like, e.g., erosion or mass transfer, have now been extensively studied. Coagulation simulations consistently show that $\rm μ$m-sized dust grains can grow to mm- to cm-sized aggregates before they encounter the bouncing barrier, whereas sub-$\rm μ$m-sized water-ice particles can directly grow to planetesimal sizes. For siliceous materials, other processes have t…
The inner part of protoplanetary disks can be threaded by strong magnetic fields. In laboratory levitation experiments, we study how magnetic fields up to 7 mT influence the aggregation of dust by observing the self-consistent collisional evolution of particle ensembles. As dust samples we use mixtures of iron and quartz in different ratios. Without magnetic fields, particles in all samples grow into a bouncing barrier. These aggregates reversibly form larger clusters in the presence of magnetic fields. The size of these clusters depends on the strength of the magnetic field and the ratio betw…
Investigating the Bouncing Barrier with Collision Simulations of Compressed Dust Aggregates
Institute of Science Tokyo（东京科学大学）；RIKEN Interdisciplinary Theoretical and Mathematical Sciences Program (iTHEMS)（理化学研究所交叉理论与数学科学项目）；Tohoku University（东北大学）
The Influence of the Fractal Dimension on Dust Evolution in Protoplanetary Disks
Institut für Theoretische Astrophysik, Zentrum für Astronomie der Universität Heidelberg（海德堡大学天体物理中心理论天体物理研究所）；Anton Pannekoek Institute for Astronomy, University of Amsterdam（阿姆斯特丹大学安顿·潘内科克天文学研究所）
The collisional evolution of solid material in protoplanetary disks is a crucial step in the formation of planetesimals, comets, and planets. Although dense protoplanetary environments favor fast dust coagulation, there are several factors that limit the straightforward pathway from interstellar micron-size grains to pebble-size aggregates. Apart from the grain bouncing, fragmentation, and fast drift to the central star, a notable limiting factor is the electrostatic repulsion of like-charged grains. In this study we aim at theoretical modeling of the dust coagulation coupled with the dust cha…
