Collision velocity of dust grains in self-gravitating protoplanetary discs.
Collision velocity of dust grains in self-gravitating protoplanetary discs.
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DOI：
10.1093/mnras/stw488
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发表时间：
2016-05-21
影响因子：
4.8
通讯作者：
Clarke CJ
中科院分区：
文献类型：
--
作者：
Booth RA;Clarke CJ
我们已经进行了第一次全面的数值调查的尘埃粒子的相对速度分布在自引力原行星盘，以评估通过直接崩溃在这样的环境中的星子形成的可行性。的可行性取决于关键的大尺寸，优先收集在压力最大值所产生的瞬态螺旋功能（斯托克斯数，St 1），这些尺寸尺度的增长需要碰撞速度保持足够低，晶粒生长不逆转破碎。我们发现，对于一个单一大小的尘埃人口，速度驱动光盘的引力扰动是有效的，只有St > 3，而耦合到气体速度占主导地位，否则。我们开发了一个标准来理解这一结果的停止距离是光盘scaleheight的顺序。尽管如此，在多尺度尘埃群中，由于不同的径向漂移所引起的相对速度太高，不允许硅酸盐尘埃颗粒生长超过St Au 10− 2或10−1（在30 Au时，10 cm到m的尺寸），这样的斯托克斯数不足以使固体集中在螺旋特征中。然而，对于冰冷的固体（它可以在高达几个10 m s-1的碰撞中存活下来），从星星到30 Au以上可能会生长到St 1（10 m大小）。这样的物体将集中在螺旋特征，并可能通过引力坍缩产生更大的冰状微行星/彗星。这些微行星将获得适度的离心率，并在圆盘的剩余寿命中保持不变。
We have conducted the first comprehensive numerical investigation of the relative velocity distribution of dust particles in self-gravitating protoplanetary discs with a view to assessing the viability of planetesimal formation via direct collapse in such environments. The viability depends crucially on the large sizes that are preferentially collected in pressure maxima produced by transient spiral features (Stokes numbers, St ∼ 1); growth to these size scales requires that collision velocities remain low enough that grain growth is not reversed by fragmentation. We show that, for a single-sized dust population, velocity driving by the disc's gravitational perturbations is only effective for St > 3, while coupling to the gas velocity dominates otherwise. We develop a criterion for understanding this result in terms of the stopping distance being of the order of the disc scaleheight. Nevertheless, the relative velocities induced by differential radial drift in multi-sized dust populations are too high to allow the growth of silicate dust particles beyond St ∼ 10− 2 or 10−1 (10 cm to m sizes at 30 au), such Stokes numbers being insufficient to allow concentration of solids in spiral features. However, for icy solids (which may survive collisions up to several 10 m s−1), growth to St ∼ 1 (10 m size) may be possible beyond 30 au from the star. Such objects would be concentrated in spiral features and could potentially produce larger icy planetesimals/comets by gravitational collapse. These planetesimals would acquire moderate eccentricities and remain unmodified over the remaining lifetime of the disc.