Much recent work on planet formation has focused on the growth of planets by accretion of grains whose aerodynamic properties make them marginally coupled to the nebular gas, a theory commonly referred to as "pebble accretion". While pebble accretion can ameliorate some of the issues presented by growth by purely gravitational processes, it has other issues when compared with observations of exoplanetary systems. A particular concern is the preponderance of planets that end their growth as "super-Earths" or "sub-Neptunes", with masses in the range 2-10 $M_\oplus$. Once planets reach this mass scale, timescales for growth by pebble accretion are so rapid that ubiquitously ending growth here is difficult. In this work, we highlight this issue in detail using our previously published model of pebble accretion, and also propose a possible solution: feedback between the growing planet's atmosphere and the gas disk inhibits accretion of smaller particle sizes by forcing them to flow around the growing planet instead of being accreted. For reasonable fiducial disk parameters this "flow isolation" will inhibit accretion of all available particle sizes once the planet reaches super-Earth masses. We also demonstrate that the characteristics of this "flow isolation mass" agree with previously published trends identified in the \textit{Kepler} planets.

中文翻译：

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流动隔离如何设定超级地球行星的质量尺度

最近关于行星形成的许多工作都集中在通过颗粒吸积来生长行星，颗粒的空气动力学特性使它们与星云气体略微耦合，这种理论通常被称为“卵石吸积”。虽然鹅卵石吸积可以改善由纯引力过程引起的一些问题，但与对系外行星系统的观察相比，它还有其他问题。一个特别令人担忧的问题是，以“超级地球”或“亚海王星”结束其生长的行星占优势，其质量在 2-10 $M_\oplus$ 范围内。一旦行星达到这种质量规模，卵石吸积增长的时间尺度如此之快，以至于在这里无处不在地结束增长是很困难的。在这项工作中，我们使用我们之前发布的卵石吸积模型详细强调了这个问题，并提出了一个可能的解决方案：正在生长的行星的大气层和气体盘之间的反馈通过迫使较小的颗粒绕着正在生长的行星流动而不是被吸积来抑制较小颗粒的吸积。对于合理的基准盘参数，一旦行星达到超地球质量，这种“流动隔离”将抑制所有可用颗粒尺寸的吸积。我们还证明了这种“流动隔离质量”的特征与之前在 \textit{Kepler} 行星中确定的趋势一致。一旦行星达到超地球质量，将抑制所有可用粒子大小的吸积。我们还证明了这种“流动隔离质量”的特征与之前在 \textit{Kepler} 行星中确定的趋势一致。一旦行星达到超地球质量，将抑制所有可用粒子大小的吸积。我们还证明了这种“流动隔离质量”的特征与之前在 \textit{Kepler} 行星中确定的趋势一致。