标题： 形成晚期M矮星周围的巨型行星：颗粒吸积和行星-行星碰撞 显示英文标题

标题： Forming Giant Planets Around Late-M Dwarfs: Pebble Accretion and Planet-Planet Collision

摘要： 我们提出了一种以岩石块为主导的核心吸积场景，用以解释围绕晚期M矮星$M_{\star}{=}0.1{-}0.2 \ M_{\odot}$形成巨行星的过程。为了探索巨行星形成的最佳盘条件，我们进行了N体模拟，研究了内外区域分别受到粘性加热和恒星辐射的盘中单个和多个原行星的增长及动力学演化。原行星的初始质量要么假设等于$0.01 \ M_{\oplus}$，要么基于流体不稳定性模拟推导出的公式计算得出。我们的发现表明，质量更大的行星更可能在寿命更长、固态质量更高、盘湍流程度适中至较高的盘中形成，并且原行星的初始质量更大。在单个原行星增长的情况下，能够达到的最大行星核质量通常低于触发快速气体吸积的阈值，这阻碍了巨行星的形成。然而，在多原行星情况下，频繁的行星-行星碰撞帮助核心突破了岩石隔离质量屏障。这加速了它们的气体吸积并促进了巨行星的形成，使得巨行星生长的最佳参数空间显著扩大。综合来看，我们的结果表明，即使在非常低质量的恒星宿主周围，当月球质量的原行星从星子吸积中首次出现并通过结合岩石吸积和行星-行星碰撞在高供给的岩石储库${>}50 \ M_{\oplus}$和湍流水平为$\alpha_{\rm t} {\sim} 10^{-3}{-}10^{-2}$的盘中迅速成长时，仍然有可能形成轨道周期为${\lesssim}100$天的巨行星。 显示英文摘要

摘要： We propose a pebble-driven core accretion scenario to explain the formation of giant planets around the late-M dwarfs of $M_{\star}{=}0.1{-}0.2 \ M_{\odot}$. In order to explore the optimal disk conditions for giant planet, we perform N-body simulations to investigate the growth and dynamical evolution of both single and multiple protoplanets in the disks with both inner viscously heated and outer stellar irradiated regions. The initial masses of the protoplanets are either assumed to be equal to $0.01 \ M_{\oplus}$ or calculated based on the formula derived from streaming instability simulations. Our findings indicate that massive planets are more likely to form in disks with longer lifetimes, higher solid masses, moderate to high levels of disk turbulence, and larger initial masses of protoplanets. In the single protoplanet growth cases, the highest planet core mass that can be reached is generally lower than the threshold necessary to trigger rapid gas accretion, which impedes the formation of giant planets. Nonetheless, in multi-protoplanet cases, the cores can exceed the pebble isolation mass barrier aided by frequent planet-planet collisions. This consequently speeds up their gas accretion and promotes giant planet formation, making the optimal parameter space to grow giant planets substantially wider. Taken together, our results suggest that even around very low-mass stellar hosts, the giant planets with orbital periods of ${\lesssim}100$ days are still likely to form when lunar-mass protoplanets first emerge from planetesimal accretion and then grow rapidly by a combination of pebble accretion and planet-planet collisions in disks with a high supply of pebble reservoir ${>}50 \ M_{\oplus}$ and turbulent level of $\alpha_{\rm t} {\sim} 10^{-3}{-}10^{-2}$.