Influences of protoplanet-induced three-dimensional gas flow on pebble accretion
Influences of protoplanet-induced three-dimensional gas flow on pebble accretion
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DOI：
10.1051/0004-6361/202039153
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发表时间：
2020-09
影响因子：
6.5
通讯作者：
Ayumu Kuwahara;H. Kurokawa
中科院分区：
文献类型：
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作者：
Ayumu Kuwahara;H. Kurokawa
上下文卵石吸积是行星形成的主要理论之一。空气动力学上的小颗粒，称为卵石，受到气流的高度影响。嵌入原行星盘中的生长行星会产生三维（3D）气体流。在我们以前的工作中，论文一，我们集中在剪切体制的卵石吸积和行星诱导的气体流的卵石吸积的影响进行了研究。在论文I中，我们发现，与未扰动气流相比，行星诱导气流中的卵石吸积是无效的，特别是当St = 10−3时，其中St是斯托克斯数。目标。根据论文I的发现，我们研究了行星引起的气流对卵石吸积的影响。我们在论文Ⅰ中没有考虑气体的逆风。在这里，我们将我们的研究扩展到卵石吸积的逆风制度。方法.假设一个非等温的，无粘性的子开普勒气体盘，我们进行了三维流体动力学模拟的球形极网格托管的行星与无量纲质量，m = RBondi scinH，位于其中心，其中RBondi和H是邦迪半径和磁盘尺度的高度，分别。然后，我们数值积分的运动方程的卵石在3D中使用流体动力学模拟数据。结果我们首先将行星引起的气流分为两个区域：气流切变和气流逆风。在剪切流区，行星引起的气流具有垂直旋转对称结构，我们发现结果与文Ⅰ中的结果一致。在流动-逆风区，气体的强逆风打破了行星诱导气流的对称结构。在流动-逆风区，我们发现在行星诱导的气流中，St = 10−3的卵石的轨迹与未扰动气流的轨迹有很大不同。循环流动，其中气体从磁盘进入引力球在低纬度和退出在高纬度，收集鹅卵石周围的行星。我们推导出流动过渡质量分析，mt，流量，区分之间的流动逆风和流动剪切制度。根据m，mt，flow与mt，peb之间的关系，其中mt，peb是卵石吸积区的过渡质量，我们将文Ⅰ和本研究的结果分成四组。特别是，只有当采用斯托克斯气体阻力定律且m < min（mt，peb，mt，flow）时，吸积和流态都处于逆风状态，与未扰动流相比，St = 10−3的卵石在行星诱导气流中的吸积概率才有所增加。结论.结合我们的研究结果与空间变化的湍流强度和卵石大小的磁盘，我们得出结论，行星引起的气体流仍然允许卵石吸积在行星形成的早期阶段。由于行星引起的气体流动对卵石吸积的抑制只发生在行星形成的后期，更具体地说，在盘的内部区域。这可能有助于解释系外行星的分布和太阳系的结构，两者都有小的内部和大的外部行星。
Context. Pebble accretion is among the major theories of planet formation. Aerodynamically small particles, called pebbles, are highly affected by the gas flow. A growing planet embedded in a protoplanetary disk induces three-dimensional (3D) gas flow. In our previous work, Paper I, we focused on the shear regime of pebble accretion and investigated the influence of planet-induced gas flow on pebble accretion. In Paper I, we found that pebble accretion is inefficient in the planet-induced gas flow compared to that of the unperturbed flow, particularly when St ≲ 10−3, where St is the Stokes number. Aims. Following on the findings of Paper I, we investigate the influence of planet-induced gas flow on pebble accretion. We did not consider the headwind of the gas in Paper I. Here, we extend our study to the headwind regime of pebble accretion. Methods. Assuming a nonisothermal, inviscid sub-Keplerian gas disk, we performed 3D hydrodynamical simulations on the spherical polar grid hosting a planet with the dimensionless mass, m = RBondi∕H, located at its center, where RBondi and H are the Bondi radius and the disk scale height, respectively. We then numerically integrated the equation of motion for pebbles in 3D using hydrodynamical simulation data. Results. We first divided the planet-induced gas flow into two regimes: flow-shear and flow-headwind. In the flow-shear regime, where the planet-induced gas flow has a vertically rotational symmetric structure, we find that the outcome is identical to what we obtained in Paper I. In the flow-headwind regime, the strong headwind of the gas breaks the symmetric structure of the planet-induced gas flow. In the flow-headwind regime, we find that the trajectories of pebbles with St ≲ 10−3 in the planet-induced gas flow differ significantly from those of the unperturbed flow. The recycling flow, where gas from the disk enters the gravitational sphere at low latitudes and exits at high latitudes, gathers pebbles around the planet. We derive the flow transition mass analytically, mt, flow, which discriminates between the flow-headwind and flow-shear regimes. From the relation between m, mt, flow and mt, peb, where mt, peb is the transition mass of the accretion regime of pebbles, we classify the results obtained in both Paper I and this study into four groups. In particular, only when the Stokes gas drag law is adopted and m < min(mt, peb, mt, flow), where the accretion and flow regime are both in the headwind regime, the accretion probability of pebbles with St ≲ 10−3 is enhanced in the planet-induced gas flow compared to that of the unperturbed flow. Conclusions. Combining our results with the spacial variety of turbulence strength and pebble size in a disk, we conclude that the planet-induced gas flow still allows for pebble accretion in the early stage of planet formation. The suppression of pebble accretion due to the planet-induced gas flow occurs only in the late stage of planet formation, more specifically, in the inner region of the disk. This may be helpful for explaining the distribution of exoplanets and the architecture of the Solar System, both of which have small inner and large outer planets.