Hydrodynamic simulations of the inner accretion flow of Sagittarius A* fuelled by stellar winds
Hydrodynamic simulations of the inner accretion flow of Sagittarius A* fuelled by stellar winds
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DOI：
10.1093/mnras/sty1146
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发表时间：
2018-05
影响因子：
4.8
通讯作者：
S. Ressler;E. Quataert;J. Stone
中科院分区：
文献类型：
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作者：
S. Ressler;E. Quataert;J. Stone
我们提出雅典娜++基于网格的，流体动力学模拟的吸积到人马座A* 通过恒星风的$\sim 30$沃尔夫-拉叶星在中央秒差距的银河系中心。这些模拟跨越了$\sim $4个数量级的半径，一直延伸到黑洞的300个引力半径，比以前的工作深入了$\sim $32 $倍。我们相当好地再现了钱德拉在中央秒差距观测到的漫射热X射线发射。小半径的吸积流是两个部分的叠加：1）一个适度非束缚的、亚开普勒的、厚的、有压力支撑的圆盘，它大多数（但不是全部）时间与顺时针恒星圆盘对齐; 2）一个束缚的、低角动量的流入，它主要沿着圆盘的南极。我们将这种结构解释为一些最内部的恒星风主导吸积的自然结果，从而产生具有广泛角动量分布的流。在模拟中包括星星S2对流动结构的影响可以忽略不计。外推我们的结果从不同的内半径模拟，我们发现$\sim$几个$\倍10^{-8} M_\odot$/yr在地平线尺度，符合约束的基础上模拟观测到的Sgr A* 的排放。这里发现的流动结构可以用作更现实的初始条件的水平尺度模拟的Sgr A*。
We present Athena++ grid-based, hydrodynamic simulations of accretion onto Sagittarius A* via the stellar winds of the $\sim 30$ Wolf-Rayet stars within the central parsec of the galactic center. These simulations span $\sim$ 4 orders of magnitude in radius, reaching all the way down to 300 gravitational radii of the black hole, $\sim 32$ times further in than in previous work. We reproduce reasonably well the diffuse thermal X-ray emission observed by Chandra in the central parsec. The resulting accretion flow at small radii is a superposition of two components: 1) a moderately unbound, sub-Keplerian, thick, pressure-supported disc that is at most (but not all) times aligned with the clockwise stellar disc, and 2) a bound, low-angular momentum inflow that proceeds primarily along the southern pole of the disc. We interpret this structure as a natural consequence of a few of the innermost stellar winds dominating accretion, which produces a flow with a broad distribution of angular momentum. Including the star S2 in the simulation has a negligible effect on the flow structure. Extrapolating our results from simulations with different inner radii, we find an accretion rate of $\sim$ a few $\times 10^{-8} M_\odot$/yr at the horizon scale, consistent with constraints based on modeling the observed emission of Sgr A*. The flow structure found here can be used as more realistic initial conditions for horizon scale simulations of Sgr A*.