弱压力凸起中流动不稳定性促进星子形成
Planetesimal formation facilitated by streaming instability in weak pressure bumps
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- Center for Star and Planet Formation, Globe Institute, University of Copenhagen（哥本哈根大学恒星与行星形成中心全球研究所）
- Niels Bohr Institute, University of Copenhagen（哥本哈根大学尼尔斯·玻尔研究所）
- Anton Pannekoek Institute for Astronomy, University of Amsterdam（阿姆斯特丹大学安东·潘内科克天体物理研究所）
- Division of Astrophysics, Department of Physics, Lund University（隆德大学物理系天体物理学部）
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中文总结 AI 辅助
本研究通过二维剪切盒模拟发现，弱压力凸起即使振幅低至0.04也能触发流动不稳定性，促进原行星盘中小卵石形成星子，并提出了新的聚集判据。
中文摘要 AI 辅助
在原行星盘中，通过小卵石的流动不稳定性形成星子，需要相对于太阳金属丰度（$Z\simeq 0.01$）增强的固体浓度。我们在此研究弱轴对称压力凸起中的堆积是否足以通过流动不稳定性触发强烈的粒子集中。使用毫米至厘米级卵石的高分辨率二维剪切盒模拟，我们探讨了在无增强压力凸起存在下流动不稳定性的行为。我们发现，即使是非常弱的凸起，其气体密度振幅低至相对于背景的 $A = 0.04$，在内盘太阳金属丰度下，对于所有测试的斯托克斯数，也能通过流动不稳定性产生致密的粒子丝状结构。外盘区域需要稍强的凸起（$A \geq 0.14$）才能在太阳金属丰度下形成丝状结构，尽管当金属丰度增加到 $Z = 0.02$ 时，所需的凸起振幅大幅降低。我们的结果表明，弱且无增强的压力凸起可以作为小卵石中通过流动不稳定性形成星子的焦点，这与先前使用增强来维持压力凸起的研究形成对比。此外，我们引入了一个依赖于压力凸起的聚集判据，$(Z/\chi)_\mathrm{crit} \approx 0.3$，其中 $\chi = \Pi_\mathrm{min}^2/\Pi_0$，在没有压力凸起时简化为背景压力梯度 $\Pi_0$。该判据概括了较低压力梯度下固体堆积的规模，并根据我们的模拟结果准确预测了强烈聚集的发生。由于压力凸起特征在观测到的年轻盘和磁流体动力学模拟中是常见特征，我们的二维模拟结果表明，弱压力凸起可能是原行星盘中星子形成的主要摇篮。
英文摘要
Planetesimal formation via the streaming instability of small pebbles in protoplanetary discs requires enhanced solid concentrations relative to the solar metallicity, $Z\simeq 0.01$. We investigate here whether pile-ups in weak axisymmetric pressure bumps are sufficient to trigger strong particle concentrations via the streaming instability. Using high-resolution 2D shearing box simulations with millimetre-to-centimetre pebbles, we explore the behaviour of the streaming instability in the presence of a non-reinforced pressure bump. We find that even very weak bumps, with gas density amplitudes as low as $A = 0.04$ relative to the background, produce dense particle filaments via the streaming instability for all tested Stokes numbers at solar metallicity in the inner disc. Outer disc regions require slightly stronger bumps ($A \geq 0.14$) to form filaments at a solar metallicity, though the necessary bump amplitude is substantially lowered when the metallicity is increased to $Z = 0.02$. Our results suggest that weak, non-reinforced pressure bumps can act as focal points for planetesimal formation via the streaming instability in small pebbles, in contrast to previous studies which used reinforcement to maintain the pressure bump. Additionally, we introduce a pressure-bump-dependent clumping criterion, $(Z/χ)_\mathrm{crit} \approx 0.3$, where $χ= Π_\mathrm{min}^2/Π_0$ reduces to the background pressure gradient $Π_0$ in the absence of a pressure bump. This criterion encapsulates the scale of solid pile-ups at lower pressure gradients and accurately predicts the onset of strong clumping based on the results of our simulations. With pressure bump signatures being common features of observed young discs and magnetohydrodynamical simulations, the results of our 2D simulations imply that weak pressure bumps may be major cradles for planetesimal formation in protoplanetary discs.
