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arXiv 1610.01643astro-ph.EP
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数十天文单位之外的气态巨行星沙漠

A desert of gas giant planets beyond tens of au

Sergei Nayakshin

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17 pages, submitted to MNRAS
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摘要：

直接的成像观测限制了被气体巨行星环绕的恒星的比例，这些气体巨行星的距离大于10天文单位，大约只有0.01。这被广泛认为表明大质量的原行星盘很少在行星质量的物体上破碎。我用数值模拟的气体块嵌入在大规模的气体盘，以表明这些意见是一致的$\sim 0.2 - 10$行星质量块每恒星出生在年轻的引力不稳定盘。三个过程快速的团块迁移，潮汐破裂和失控的气体吸积破坏或将所有模拟的团块转化为其他物体，导致气体巨星的沙漠超过约10 au的分离。圆盘的冷却速度控制着这三个过程中哪一个占主导地位。当冷却速率快于几个局部动力学时间时，团块总是快速成长，成为大质量的棕矮星或低质量恒星。对于较长的冷却时间，坍缩后（高密度）的行星向内迁移到$\sim 10-20$ au，在那里它们在圆盘上打开一个缺口，然后继续向内迁移，速度要慢得多。坍缩前（低密度）的行星被潮汐破坏，可能会留下巨大的固体核心。在沙漠内观察到的气态巨行星，例如HR 8799中的行星，一定遵循了一条不寻常的进化路径，例如，它们的主盘以灾难性的方式被分散。

英文摘要：

Direct imaging observations constrain the fraction of stars orbited by gas giant planets with separations greater than 10 au to about 0.01 only. This is widely believed to indicate that massive protoplanetary discs rarely fragment on planetary mass objects. I use numerical simulations of gas clumps embedded in massive gas discs to show that these observations are consistent with $\sim 0.2 - 10$ planetary mass clumps per star being born in young gravitationally unstable discs. A trio of processes -- rapid clump migration, tidal disruption and runaway gas accretion -- destroys or transforms all of the simulated clumps into other objects, resulting in a desert of gas giants beyond separation of approximately 10 au. The cooling rate of the disc controls which of the three processes is dominant. For cooling rates faster than a few local dynamical times, clumps always grow rapidly and become massive brown dwarfs or low mass stars. For longer cooling times, post-collapse (high density) planets migrate inward to $\sim 10-20$ au where they open a gap in the disc and then continue to migrate inward much less rapidly. Pre-collapse (low density) planets are tidally disrupted and may leave massive solid cores behind. Gas giant planets observed inside the desert, such as those in HR 8799, must have followed an unusual evolutionary path, e.g., their host disc being dispersed in a catastrophic fashion.

机构、总结、中文摘要均由AI分析而来，可能存在错误，请以论文正文为准。

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