Can Stellar-mass Black Hole Growth Disrupt Disks of Active Galactic Nuclei? The Role of Mechanical Feedback
Can Stellar-mass Black Hole Growth Disrupt Disks of Active Galactic Nuclei? The Role of Mechanical Feedback
复制标题
DOI：
10.3847/1538-4357/ac45f8
复制
发表时间：
2021-12
期刊：
影响因子：
--
通讯作者：
H. Tagawa;S. Kimura;Z. Haiman;R. Perna;Hidekazu Tanaka;I. Bartos
中科院分区：
文献类型：
--
作者：
H. Tagawa;S. Kimura;Z. Haiman;R. Perna;Hidekazu Tanaka;I. Bartos
由于引力拖曳和原位恒星形成，恒星质量的 BH（sBH）预计会嵌入活动星系核（AGN）盘中。然而，我们发现，由于 AGN 盘环境中的气体密度较高，致密天体可能会迅速生长为中等质量的 BH，并耗尽 AGN 盘中的物质，除非通过某些反馈过程抑制吸积。这些后果与活动星系核的观测结果和银河系中心的动态不一致。在这里，我们考虑减少气体积聚的机械反馈机制。快速吸积的超黑洞通过布兰德福德-兹纳耶克机制发射风和/或喷射，产生高压冲击和茧。这种冲击和茧可以在盘面横向扩散，弹出环绕 sBH 盘（CsBD）的外部区域，并在 AGN 盘上刺穿一个水平尺寸与盘尺度高度相当的孔。由于束缚 CsBD 的耗尽时间尺度比向 sBH 重新供应气体的时间尺度要短得多，因此该过程将 sBH 上的时间平均吸积率降低了约 10-100 倍。因此，这种反馈机制可以帮助缓解 sBH 过度增长和 AGN 盘耗尽问题。另一方面，我们发现喷流茧可以解开质量较小的超大质量黑洞（SMBH）盘中积聚的大部分气体，这可能有助于解释SMBH质量≲ 105 M ⊙的高爱丁顿比活动星系核的缺乏。
Stellar-mass BHs (sBHs) are predicted to be embedded in active galactic nucleus (AGN) disks owing to gravitational drag and in situ star formation. However, we find that, due to a high gas density in an AGN disk environment, compact objects may rapidly grow to intermediate-mass BHs and deplete matter from the AGN disk unless accretion is suppressed by some feedback process(es). These consequences are inconsistent with AGN observations and the dynamics of the Galactic center. Here we consider mechanical feedback mechanisms for the reduction of gas accretion. Rapidly accreting sBHs launch winds and/or jets via the Blandford–Znajek mechanism, which produce high-pressure shocks and cocoons. Such a shock and cocoon can spread laterally in the plane of the disk, eject the outer regions of a circum-sBH disk (CsBD), and puncture a hole in the AGN disk with horizontal size comparable to the disk scale height. Since the depletion timescale of the bound CsBD is much shorter than the resupply timescale of gas to the sBH, the time-averaged accretion rate onto sBHs is reduced by this process by a factor of ∼10–100. This feedback mechanism can therefore help alleviate the sBH overgrowth and AGN disk depletion problems. On the other hand, we find that cocoons of jets can unbind a large fraction of the gas accreting in the disks of less massive supermassive BHs (SMBHs), which may help explain the dearth of high-Eddington-ratio AGNs with SMBH mass ≲ 105 M ⊙.