In recent years, near-IR and X-ray flares have been detected from the Galaxy's central radio point source, Sagittarius A~* (Sgr A~*), believed to be an ～3 x 10~6 solar mass supermassive black hole. In some cases, the transient emission appears to be modulated with a (quasi-)periodic oscillation (QPO) of ～ 17-20 minutes. The implied ～3r_s size of the emitter (where r_s ≡ 2GM/c~2 is the Schwarzschild radius) points to an instability—possibly induced by accretion—near the marginally stable orbit (MSO) of a slowly spinning object. But Sgr A~* is not accreting via a large, "standard" disk; instead, the low-density environment surrounding it apparently feeds the black hole with low angular momentum clumps of plasma that circularize within ?(10-300)r_s and merge onto a compact, hot disk. In this Letter, we follow the evolution of the disk following such an event, and we show that a Rossby wave instability, particularly in its magnetohydrodynamic (MHD) form, grows rapidly and produces a period of enhanced accretion lasting several hours. Both the amplitude of this response and its duration match the observed flare characteristics rather well.
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机译：近年来，从银河系中央无线电点源射手座A〜*（Sgr A〜*）探测到近红外和X射线耀斑，据信这是一个约3 x 10〜6太阳质量超大质量黑洞。在某些情况下，瞬态发射似乎由〜17-20分钟的（准）周期性振荡（QPO）调制。发射器的〜3r_s的隐含大小（其中r_s≡2GM / c〜2是Schwarzschild半径）表示不稳定，可能是由于吸积引起的，它靠近缓慢旋转的物体的边缘稳定轨道（MSO）。但是Sgr A〜*不会通过大型的“标准”磁盘进行积聚。取而代之的是，围绕它的低密度环境显然为黑洞提供了低等离子角动量团块，这些团块在φ（10-300）r_s内圆形化并合并到紧凑的热盘上。在这封信中，我们跟踪了此类事件之后磁盘的演化，并且我们证明了罗斯比波不稳定性，尤其是其磁流体动力学（MHD）形式的不稳定性迅速增长，并产生了持续数小时的增强吸积期。该响应的幅度及其持续时间都与观测到的耀斑特性非常匹配。
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