银河系中心微螺旋区热不稳定性的条件
Conditions for the Thermal Instability in the Galactic Centre Mini-spiral region
摘要：
我们探讨的条件下，在银河系中心（Sgr A*），在那里的热和冷介质是已知的共存的微型螺旋区域的热不稳定性。对不同物理状态的等离子体进行了光电离云计算。我们忽略了材料的动力学，并集中在热不稳定性可能运作的参数范围的研究，考虑到过去的历史Sgr A* 测热光度。我们表明，热不稳定性不工作在目前非常低的水平的Sgr A* 活动。然而，Sgr A* 在过去更加明亮。对于最高的光度状态，两相介质可以从中心产生1.4 pc。尘埃颗粒的存在往往会抑制不稳定性，但在强辐射场和热等离子体的存在下，尘埃被破坏。因此，在高活动期诱导成团，并且冷却/加热时间尺度足够长以稍后保留过去的多相结构。这种不稳定性增强了小型螺旋介质的团块性，并可能导致冷团块向Sgr A* 增强吸积。该机制决定了云的质量和大小范围，在Sgr A* 条件下，云典型质量的可能值为$1$ - $10^2M_{\oplus}$。
英文摘要：
We explore the conditions for the thermal instability to operate in the mini-spiral region of the Galactic centre (Sgr A*), where both the hot and cold media are known to coexist. The photoionisation Cloudy calculations are performed for different physical states of plasma. We neglect the dynamics of the material and concentrate on the study of the parameter ranges where the thermal instability may operate, taking into account the past history of Sgr A* bolometric luminosity. We show that the thermal instability does not operate at the present very low level of the Sgr A* activity. However, Sgr A* was much more luminous in the past. For the highest luminosity states the two-phase medium can be created up to 1.4 pc from the centre. The presence of dust grains tends to suppress the instability, but the dust is destroyed in the presence of strong radiation field and hot plasma. The clumpiness is thus induced in the high activity period, and the cooling/heating timescales are long enough to preserve later the past multi-phase structure. The instability enhances the clumpiness of the mini-spiral medium and creates a possibility of episodes of enhanced accretion of cold clumps towards Sgr A*. The mechanism determines the range of masses and sizes of clouds; under the conditions of Sgr A*, the likely values come out $1$ - $10^2M_{\oplus}$ for the cloud typical mass.
机构、总结、中文摘要均由AI分析而来，可能存在错误，请以论文正文为准。
