Planet Formation around Supermassive Black Holes in the Active Galactic Nuclei
Planet Formation around Supermassive Black Holes in the Active Galactic Nuclei
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DOI：
10.3847/1538-4357/ab4cf0
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发表时间：
2019-09
期刊：
影响因子：
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通讯作者：
K. Wada;Y. Tsukamoto;E. Kokubo
中科院分区：
文献类型：
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作者：
K. Wada;Y. Tsukamoto;E. Kokubo
作为尘埃生长基本过程的自然结果，我们发现一类新的行星可以在超大质量黑洞（SMBH）周围形成。我们研究了从亚微米大小的冰尘单体到地球大小的机构以外的“雪线”，位于几个秒差距的SMBH在低光度活动星系核（AGN）的增长路径。与原行星盘相反，“径向漂移障碍”并不能阻止星子的形成。在演化的早期阶段，尘埃粒子之间的低碰撞速度促进粘附，因此，尘埃聚集体的内部密度随着生长而减小。当多孔聚集体的尺寸达到0.1- 1cm时，碰撞压缩变得有效，并且内部密度的降低停止。一旦10-100米大小的聚集体形成，它们就与气体湍流分离，聚集层变得重力不稳定，导致通过层的破碎形成行星，其质量是地球的10倍。增长时间尺度取决于环核盘的湍流强度和黑洞质量MBH，对于低质量（MBH <$106M <$）SMBH，它与活动星系核的寿命（108年）相当。
As a natural consequence of the elementary processes of dust growth, we discovered that a new class of planets can be formed around supermassive black holes (SMBHs). We investigated a growth path from submicron sized icy dust monomers to Earth-sized bodies outside the “snow line,” located several parsecs from SMBHs in low luminosity active galactic nuclei (AGNs). In contrast to protoplanetary disks, the “radial drift barrier” does not prevent the formation of planetesimals. In the early phase of the evolution, low collision velocity between dust particles promotes sticking; therefore, the internal density of the dust aggregates decreases with growth. When the porous aggregate’s size reaches 0.1–1 cm, the collisional compression becomes effective, and the decrease in internal density stops. Once 10–100 m sized aggregates are formed, they are decoupled from gas turbulence, and the aggregate layer becomes gravitationally unstable, leading to the formation of planets by the fragmentation of the layer, with 10 times the mass of the Earth. The growth timescale depends on the turbulent strength of the circumnuclear disk and the black hole mass MBH, and it is comparable to the AGN’s lifetime (∼108 yr) for low mass (MBH ∼ 106M⊙) SMBHs.