Co-Accretion of Chondrules and Dust in the Solar Nebula
Co-Accretion of Chondrules and Dust in the Solar Nebula
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太阳星云中球粒和尘埃的共同吸积
DOI：
10.1086/587836
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发表时间：
2008
期刊：
影响因子：
--
通讯作者：
A. Tielens
中科院分区：
文献类型：
--
作者：
C. Ormel;J. N. Cuzzi;A. Tielens
我们提出了一种球粒粘合在一起的机制，这是通过压缩它们在尘埃星云气体中移动时扫过的多孔尘埃边缘来实现的。结果表明，微米级颗粒形成的粉尘聚集体附着在球粒上，形成疏松的粉尘边缘。当球粒碰撞时，这些尘埃可以通过在多孔尘埃层内的滚动运动来压缩。这种机制消散了碰撞能量，压缩了球粒边缘，使球粒得以粘连。所获得的球粒尘埃凝聚体(称为化合物)的结构由三个相组成：球粒尘埃、多孔尘埃和被碰撞压实的尘埃。随后，这些化合物附着在自己的尘埃中，并与其他化合物相撞。用蒙特卡罗程序计算了化合物尺寸分布的演化和各相的相对重要性。生长结束，当化合物中的所有灰尘都被压实时，模拟终止。进行了多次运行，反映了球粒形成时物理条件的不确定性。研究发现，当湍流度较低时，化合物的半径可增大1-2个数量级，最大可达dm。然而，与径向漂移相关的相对速度形成了进一步增长的障碍。早些时候的研究结果证实了球粒所卷起的尘埃与其大小成比例。我们对比了两种情况，即这种尘埃如何进一步向球粒陨石中所见的密集边缘演化。
We present a mechanism for chondrules to stick together by means of compaction of a porous dust rim they sweep up as they move through the dusty nebula gas. It is shown that dust aggregates formed out of micron-size grains stick to chondrules, forming a porous dust rim. When chondrules collide, this dust can be compacted by means of rolling motions within the porous dust layer. This mechanism dissipates the collisional energy, compacting the rim and allowing chondrules to stick. The structure of the obtained chondrule-dust agglomerates (referred to as compounds) then consists of three phases: chondrules, porous dust, and dust that has been compacted by collisions. Subsequently, these compounds accrete their own dust and collide with other compounds. The evolution of the compound size distribution and the relative importance of the phases is calculated by a Monte Carlo code. Growth ends, and a simulation is terminated when all the dust in the compounds has been compacted. Numerous runs are performed, reflecting the uncertainty in the physical conditions at the chondrule formation time. It is found that compounds can grow by 1-2 orders of magnitudes in radius, up to dm sizes when turbulence levels are low. However, relative velocities associated with radial drift form a barrier for further growth. Earlier findings that the dust sweep-up by chondrules is proportional to their sizes are confirmed. We contrast two scenarios regarding how this dust evolved further toward the densely packed rims seen in chondrites.