Electrical charging overcomes the bouncing barrier in planet formation
Electrical charging overcomes the bouncing barrier in planet formation
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DOI：
10.1038/s41567-019-0728-9
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发表时间：
2020-02-01
期刊：
影响因子：
19.6
通讯作者：
Wurm, Gerhard
中科院分区：
文献类型：
--
作者：
Steinpilz, Tobias;Joeris, Kolja;Wurm, Gerhard
在原行星盘中，固体物体（所谓的星子）是由尘埃形成的。微米大小的尘埃颗粒会长成毫米大小的聚集体。一旦这些聚集体的直径超过几厘米，它们就会受到诸如流不稳定性等集中机制的影响，从而形成自引力星团，这些星团最终可能坍缩成千米大小的星子。然而，为了使流的不稳定性开始，原行星盘的中心需要有从厘米到分米大小的团块。在毫米和厘米之间的大小范围内，聚集体相互反弹而不是粘在一起，并且生长停滞。在微重力实验中，我们展示了毫米大小的颗粒之间的碰撞导致足够的电荷聚集，以弥补弹跳屏障和流不稳定性开始之间的差距。我们计算模拟了聚合，发现只有在电荷存在的情况下，模型才与实验数据一致。因此，我们提出碰撞充电可能会促进目前的星子形成模型无法解释的尺寸差距的早期增长。在我们对行星形成的理解中，我们仍然不清楚毫米大小的尘埃颗粒是如何长成厘米大小的聚集体的。微重力实验现在表明，颗粒的电荷导致形成更大的团块。
In protoplanetary disks, solid objects (so-called planetesimals) are formed from dust. Micrometre-sized dust grains grow into millimetre-sized aggregates. Once those aggregates have diameters exceeding a few centimetres, they become subject to concentration mechanisms such as the streaming instability, permitting the formation of self-gravitating clusters, which might eventually collapse into kilometre-sized planetesimals. However, for the streaming instability to set in, clumps spanning sizes from centimetres to decimetres are required in the centre of a protoplanetary disk. In the size range between millimetres and centimetres, aggregates bounce off each other rather than sticking together, and growth is stalled. Here we show in microgravity experiments that collisions between millimetre-sized grains lead to sufficient electrical charging for aggregation to bridge this gap between the bouncing barrier and the onset of the streaming instability. We computationally simulate aggregation and find that models agree with the experimental data only if electrical charging is present. We therefore propose that collisional charging may promote early growth in the size gap that current models of planetesimal formation cannot account for.In our understanding of planetary formation, it is still unclear how millimetre-sized dust grains grow into centimetre-sized aggregates. Microgravity experiments now show that electrical charging of the grains leads to the formation of larger clumps.