The Effect of Protoplanetary Disk Cooling Times on the Formation of Gas Giant Planets by Gravitational Instability
The Effect of Protoplanetary Disk Cooling Times on the Formation of Gas Giant Planets by Gravitational Instability
复制标题
原行星盘冷却时间对引力不稳定形成气态巨行星的影响
DOI：
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发表时间：
2017
期刊：
影响因子：
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通讯作者：
A. Boss
中科院分区：
文献类型：
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作者：
A. Boss
有观测证据表明，在年轻恒星周围的宽轨道上，由于盘引力不稳定性而形成了气体巨行星，但盘不稳定性和核心吸积在形成短周期轨道上的气体巨行星中的作用还不太清楚。争议延伸到人口合成模型的系外行星人口和流体动力学模型的碎裂过程。后者主要是指在三维（3D）流体动力学模型，控制加热和冷却过程中的重力不稳定盘，从而形成密集的团块的辐射传输的处理。本文提出了一套使用β冷却近似的模型。初始盘的质量为0.091 M，在1 M原恒星周围从4到20 Au。初始最小Toomre Qi值的范围为1.3至2.7，而β的范围为1至100。我们证明了Qi的选择与假设的β值同等重要：当初始盘温度作为下限时，对于小的β，高Qi盘可以是稳定的，而对于高β，低Qi盘可以碎裂。这些结果意味着，在评估盘碎裂的可能性时，必须考虑到盘向低Qi的演化，至少在内部盘，即，大约20个Au。这些模型表明，如果低Qi盘能够形成，那么应该有一群尚未被发现的气体巨星围绕着大约6 Au和16 Au之间的G矮星运行。
Observational evidence exists for the formation of gas giant planets on wide orbits around young stars by disk gravitational instability, but the roles of disk instability and core accretion for forming gas giants on shorter period orbits are less clear. The controversy extends to population synthesis models of exoplanet demographics and to hydrodynamical models of the fragmentation process. The latter refers largely to the handling of radiative transfer in three-dimensional (3D) hydrodynamical models, which controls heating and cooling processes in gravitationally unstable disks, and hence dense clump formation. A suite of models using the β cooling approximation is presented here. The initial disks have masses of 0.091 M⊙ and extend from 4 to 20 au around a 1 M⊙ protostar. The initial minimum Toomre Qi values range from 1.3 to 2.7, while β ranges from 1 to 100. We show that the choice of Qi is equal in importance to the β value assumed: high Qi disks can be stable for small β, when the initial disk temperature is taken as a lower bound, while low Qi disks can fragment for high β. These results imply that the evolution of disks toward low Qi must be taken into account in assessing disk fragmentation possibilities, at least in the inner disk, i.e., inside about 20 au. The models suggest that if low Qi disks can form, there should be an as yet largely undetected population of gas giants orbiting G dwarfs between about 6 au and 16 au.