Recent ALMA observations have revealed that a large fraction of protoplanetary discs contain bright rings at (sub)millimetre wavelengths. Dust trapping induced by pressure maxima in the gas disc is a popular explanation for these rings. However, it is unclear whether such pressure bumps can survive for evolutionary time-scales of the disc. In this work, we investigate an alternative scenario, which involves only dust–gas interactions in a smooth gas disc. We postulate that ALMA rings are a manifestation of a dense, clumpy mid-plane that is actively forming planetesimals. The clumpy medium itself hardly experiences radial drift, but clumps lose mass by disintegration and vertical transport and planetesimal formation. Starting from a seed ring, we numerically solve the transport equations to investigate the ring’s survival. In general, rings move outwards due to diffusion of the clump component. Without pressure support, rings leak material at rates ∼40 ${\rm M}_\oplus \, \mathrm{Myr}^{-1}$ and in order for rings to survive, they must feed from an external mass reservoir of pebbles. In the case where the pebble size is constant in the disc, a cycle between ring formation and dispersion emerges. Rings produce large quantities of planetesimals, which could be material for planet formation and explain the massive budget inferred debris disc. Mock images of ALMA observations compare well to the rings of Elias 24 and AS 209 from DSHARP’s sample.

中文翻译：

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在没有压力最大值的情况下 ALMA 环的生存

最近的 ALMA 观测表明，大部分原行星盘包含（亚）毫米波长的明亮环。由气体盘中的压力最大值引起的灰尘捕集是这些环的流行解释。然而，尚不清楚这种压力波动是否能在圆盘的进化时间尺度上存活下来。在这项工作中，我们研究了一种替代方案，该方案仅涉及光滑气盘中的尘埃-气体相互作用。我们假设 ALMA 环是一个密集的、块状的中平面的表现，它正在积极地形成小行星。块状介质本身几乎不经历径向漂移，但块状物质会因解体、垂直传输和小行星形成而失去质量。从种子环开始，我们对传输方程进行数值求解以研究环的生存情况。一般来说，由于团块成分的扩散，环向外移动。在没有压力支持的情况下，环以 ∼40 ${\rm M}_\oplus \, \mathrm{Myr}^{-1}$ 的速率泄漏材料，并且为了使环能够存活，它们必须从外部质量储存器中供给鹅卵石。在圆盘中卵石尺寸恒定的情况下，会出现环形成和分散之间的循环。环产生大量星子，这可能是行星形成的材料，并解释了推断出的大量预算碎片盘。ALMA 观测的模拟图像与 DSHARP 样本中的 Elias 24 和 AS 209 环相得益彰。在圆盘中卵石尺寸恒定的情况下，会出现环形成和分散之间的循环。环产生大量星子，这可能是行星形成的材料，并解释了推断出的大量预算碎片盘。ALMA 观测的模拟图像与 DSHARP 样本中的 Elias 24 和 AS 209 环相得益彰。在圆盘中卵石尺寸恒定的情况下，会出现环形成和分散之间的循环。环产生大量星子，这可能是行星形成的材料，并解释了推断出的大量预算碎片盘。ALMA 观测的模拟图像与 DSHARP 样本中的 Elias 24 和 AS 209 环相得益彰。