银心自引力吸积盘的有限寿命
The Limited Lifetime of Self-Gravitating Accretion Disks In Galactic Centers
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中文总结 AI 辅助
该研究分析AGN中全局自引力吸积盘的不稳定性，得出其寿命仅约10^3-4年，重建需超10^7年，解释其未被观测到的原因，认为观测到的开普勒脉泽盘或为其残余物。
中文摘要 AI 辅助
文献中频繁讨论活动星系核（AGN）中的全局自引力吸积盘，但从未被观测到。已探测到几十个AGN中的巨脉泽吸积盘，它们在0.1-1 pc尺度上呈现清晰的开普勒旋转，可估算其在中心超大质量黑洞（SMBH）影响球（SoI）内的质量，该质量比母SMBH质量小10倍以上。此外，SoI深处的恒星成分远小于质量为M_BH~几×10^6 - 几×10^7 M☉的SMBH质量。理论上，AGN中的气体盘在大小和质量上没有限制，原则上可超过其中心致密天体的质量。我们分析气体盘中可能发生的不稳定性，即局域主导自引力时的碎裂，以及全局自引力盘的轴向对称自发破缺。我们利用气体对后一种不稳定性的响应，该响应会导致引力坍缩，留下可忽略的质量和动力学稳定的残余物。因此，AGN中全局自引力盘存在的特征时标不应超过几次旋转，对于M_BH~10^6-8 M☉，t_phi~10^3-4年。盘的重建预计需要>10^7年，意味着发现概率<10^-3，这解释了它们未被探测到的原因。我们得出结论，观测到的AGN亚秒差距盘，至少是开普勒脉泽盘，可作为全局自引力吸积盘的残余物，且不稳定性时标可与AGN的工作周期相关，t_duty~10t_phi~10^4-5年。
英文摘要
Globally self-gravitating accretion disks in active galactic nuclei (AGN) have been frequently discussed in the literature, but never observed. Few dozen mega-masering accretion disks in AGN have been detected, which display a clear Keplerian rotation on scales of 0.1-1 pc, allowing to estimate their masses within the sphere of influence (SoI) of the central supermassive black holes (SMBHs) to be smaller by more than a factor of 10, compared with the parent SMBH masses. Furthermore, the stellar components, deep inside the SoI, are dwarfed by the SMBH masses of M_BH ~ few X 10^6 - few X 10^7 Mo. Theoretically, no limit exists on sizes and masses of gaseous disks in AGN, which in principle, can exceed masses of their central compact objects. We analyze instabilities which can operate in gaseous disks, i.e., fragmentation for a locally dominant self-gravity and spontaneous breaking of axial symmetry for the globally self-gravitating disks. We invoke the gas response to the latter instability which leads to gravitational collapse, leaving a negligible mass behind and dynamically stable remnants. Consequently, the characteristic timescale for globally self-gravitating disks to exist in AGN should not exceed few rotations, t_phi ~ 10^{3-4} yrs for M_BH ~ 10^{6-8} Mo. Disk rebuilding is expected to be > 10^7 yrs, meaning that probability of finding is < 10^{-3}, which explains their lack of detection. We conclude that observed sub-parsec disks in AGN, at least the Keplerian masering ones, can be remnants of globally self-gravitating accretion disks, and the instability timescale can be related to the duty cycle of AGN, t_duty ~ 10t_phi ~ 10^{4-5} yr.
