arXiv 0710.52072007-10-29astro-ph

大质量黑洞双星的诞生

Birth of massive black hole binaries

M. Colpi, M. Dotti, L. Mayer, S. Kazantzidis

备注：: To appear in "2007 STScI Spring Symposium: Black Holes", eds. M. Livio & A. M. Koekemoer, Cambridge University Press, 25 pages, 12 figures

摘要：

如果大质量黑洞（BH）在星系中无处不在，并且星系在宇宙组装过程中经历多次合并，那么BH双星应该是大多数星系凸起的常见但暂时的特征。从观测上看，活跃黑洞对的缺乏表明黑洞的寿命远短于哈勃时间，这表明黑洞的快速螺旋下降到引力波导致它们合并的区域。在这里，我们回顾了一系列的研究动态的大规模BH在富含气体的星系合并，强调了重要的作用，促进快速形成的BH二进制的冷却，气体成分。BH双星被发现位于一个巨大的自引力核盘的中心，该核盘是由母星系中的两个气体盘碰撞产生的。硬化重力扭矩对气体在这个宏伟的光盘被发现继续下降到分秒差距尺度。偏心率随时间减小到零，当双星是圆形时，吸积集在两个黑洞周围。当这种情况发生时，每个黑洞都被赋予了自己的小尺寸（< 0.01 pc）吸积盘，包括黑洞质量的几个百分比。双重活动星系核活动预计将在<100万年的时间尺度上发生。可能出现的双核点状源具有典型的< 10 pc的分离，并且可能嵌入仍在进行的星暴中。我们注意到，在气体环境中，二元失速的潜在威胁可能来自BH的辐射和/或机械能注入。只有短暂的或亚爱丁顿吸积事件可以保证持续的BH螺旋所需的双星周围的致密冷气体结构的持久性。

英文摘要：

If massive black holes (BHs) are ubiquitous in galaxies and galaxies experience multiple mergers during their cosmic assembly, then BH binaries should be common albeit temporary features of most galactic bulges. Observationally, the paucity of active BH pairs points toward binary lifetimes far shorter than the Hubble time, indicating rapid inspiral of the BHs down to the domain where gravitational waves lead to their coalescence. Here, we review a series of studies on the dynamics of massive BHs in gas-rich galaxy mergers that underscore the vital role played by a cool, gaseous component in promoting the rapid formation of the BH binary. The BH binary is found to reside at the center of a massive self-gravitating nuclear disc resulting from the collision of the two gaseous discs present in the mother galaxies. Hardening by gravitational torques against gas in this grand disc is found to continue down to sub-parsec scales. The eccentricity decreases with time to zero and when the binary is circular, accretion sets in around the two BHs. When this occurs, each BH is endowed with it own small-size (< 0.01 pc) accretion disc comprising a few percent of the BH mass. Double AGN activity is expected to occur on an estimated timescale of < 1 Myr. The double nuclear point-like sources that may appear have typical separation of < 10 pc, and are likely to be embedded in the still ongoing starburst. We note that a potential threat of binary stalling, in a gaseous environment, may come from radiation and/or mechanical energy injections by the BHs. Only short-lived or sub-Eddington accretion episodes can guarantee the persistence of a dense cool gas structure around the binary necessary for continuing BH inspiral.

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