THE REBOUND CONDITION OF DUST AGGREGATES REVEALED BY NUMERICAL SIMULATION OF THEIR COLLISIONS
THE REBOUND CONDITION OF DUST AGGREGATES REVEALED BY NUMERICAL SIMULATION OF THEIR COLLISIONS
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DOI：
10.1088/0004-637x/737/1/36
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发表时间：
2011-08
期刊：
影响因子：
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通讯作者：
K. Wada;Hidekazu Tanaka;Toru Suyama;H. Kimura;Tetsuo Yamamoto
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作者：
K. Wada;Hidekazu Tanaka;Toru Suyama;H. Kimura;Tetsuo Yamamoto
尘埃聚集体的碰撞增长是原行星盘中微行星形成的一个可能的根源。然而，碰撞尘埃聚集体的反弹阻止了尘埃成长为星子。实际上，在实验室实验中观察到反弹骨料，但在以前的数值模拟中没有观察到。因此，为了更好地理解尘埃的生长和星子的形成过程，必须弄清尘埃聚集体之间的反弹条件。我们进行了数值模拟的聚集体碰撞的各种类型的聚集体，并成功地再现碰撞聚集体在特定条件下的反弹。我们发现，在反弹过程中，聚集体结构的关键因素是配位数，即与颗粒接触的颗粒的数量。反弹是由能量耗散沿着重组的聚集体和一个大的配位数抑制重组在碰撞。我们对各种聚集体的数值模拟结果表明，当平均配位数小于6时，只要它们的碰撞速度小于破碎的临界速度，它们就会相互粘附，而不管它们的材料和结构如何。配位数的这一标准对应的填充因子为0.03，比实验室实验中报道的稍大。在原行星盘中，尘埃聚集体在其生长过程中的体积密度很低（<0.1 g cm−3），这将阻止尘埃聚集体反弹。这一结果支持了在原行星盘中直接尘埃生长的星子的形成。
Collisional growth of dust aggregates is a plausible root of planetesimals forming in protoplanetary disks. However, a rebound of colliding dust aggregates prevents dust from growing into planetesimals. In fact, rebounding aggregates are observed in laboratory experiments but not in previous numerical simulations. Therefore, the condition of rebound between dust aggregates should be clarified to better understand the processes of dust growth and planetesimal formation. We have carried out numerical simulations of aggregate collisions for various types of aggregates and succeeded in reproducing a rebound of colliding aggregates under specific conditions. Our finding is that in the rebound process, the key factor of the aggregate structure is the coordination number, namely, the number of particles in contact with a particle. A rebound is governed by the energy dissipation along with restructuring of the aggregates and a large coordination number inhibits the restructuring at collisions. Results of our numerical simulation for various aggregates indicate that they stick to each other when the mean coordination number is less than 6, regardless of their materials and structures, as long as their collision velocity is less than the critical velocity for fragmentation. This criterion of the coordination number would correspond to a filling factor of ∼0.3, which is somewhat larger than that reported in laboratory experiments. In protoplanetary disks, dust aggregates are expected to have low bulk densities (<0.1 g cm−3) during their growth, which would prevent dust aggregates from rebounding. This result supports the formation of planetesimals with direct dust growth in protoplanetary disks.