星系核中超大质量黑洞双星的演化和喷流进动的加速
Evolution of Supermassive Black Hole Binary and Acceleration of Jet Precession in Galactic Nuclei
摘要：
在星系形成的分级模型中，超大质量黑洞双星（SMBHB）是一个有希望的发现.目前，主导SMBHB演化的物理过程尚不清楚。一个有趣的问题是，我们是否可以通过观测确定SMBHB的演化，并给出物理过程的约束。在许多活动星系核中都观测到了喷流的进动现象，并将其归因于星系盘的进动。本文计算了喷流进动随时间的变化，得出了在SMBHB系统中喷流进动加速而在其它系统中喷流进动减速的结论。喷流进动$dP_{\rm pr} / dt$的加速度与喷流进动时标$P_{\rm pr}$和SMBHB演化时标$τ_{\rm a}$、${dP_{\rm pr} \over dt} \simeq - Λ{P_{\rm pr} \over τ_{\rm a}}$有关。基于喷流进动和SMBHB演化模型的计算表明，$dP_{\rm pr} / dt$可高达$- 1.0$，典型值为-0.2，并且易于检测。我们讨论了文献中观察到的NGC 1275的差异喷流进动。如果观测到的喷流进动的快速加速是真实的，那么喷流进动是由于质量比为$q\approx 0.76$的未结合SMBHB的轨道运动。当喷流从古气泡进动到当前活动喷流时，SMBHB的分离度从$1.46 {\rm Kpc}$减小到$0.80 {\rm Kpc}$，平均速度为$da/dt \simeq - 1.54 \times 10^6 {\rm cm/s}$，演化时间为$τ_{\rm a} \approx 7.5\times 10^7 {\rm yr}$。然而，如果我们假设一个稳定的射流进动许多周期，观察意味着一个硬SMBHB与质量比$q\approx 0.21$和分离$a\approx 0.29 {\rm pc}$。
英文摘要：
Supermassive black hole binary (SMBHB) is expected with the hierarchical galaxy formation model. Currently, physics processes dominating the evolution of a SMBHB are unclear. An interesting question is whether we could observationally determine the evolution of SMBHB and give constraints on the physical processes. Jet precession have been observed in many AGNs and generally attributed to disk precession. In this paper we calculate the time variation of jet precession and conclude that jet precession is accelerated in SMBHB systems but decelerated in others. The acceleration of jet precession $dP_{\rm pr} / dt$ is related to jet precession timescale $P_{\rm pr}$ and SMBHB evolution timescale $τ_{\rm a}$, ${dP_{\rm pr} \over dt} \simeq - Λ{P_{\rm pr} \over τ_{\rm a}}$. Our calculations based on the models for jet precession and SMBHB evolution show that $dP_{\rm pr} / dt$ can be as high as about $- 1.0$ with a typical value -0.2 and can be easily detected. We discussed the differential jet precession for NGC1275 observed in the literature. If the observed rapid acceleration of jet precession is true, the jet precession is due to the orbital motion of an unbound SMBHB with mass ratio $q\approx 0.76$. When jets precessed from the ancient bubbles to the currently active jets, the separation of SMBHB decrease from about $1.46 {\rm Kpc}$ to $0.80 {\rm Kpc}$ with an averaged decreasing velocity $da/dt \simeq - 1.54 \times 10^6 {\rm cm/s}$ and evolution timescale $τ_{\rm a} \approx 7.5\times 10^7 {\rm yr}$. However, if we assume a steady jet precession for many cycles, the observations implies a hard SMBHB with mass ratio $q\approx 0.21$ and separation $a\approx 0.29 {\rm pc}$.
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