是什么让吸积盘MAD
What really makes an accretion disc MAD
摘要：
黑洞（BH）周围的磁制动吸积盘（MAD）有可能刺激产生强大的喷流，并解释了最近的超高分辨率观测BH环境。它们的主要特性通常归因于整个被捕区域动态显著的净磁（垂直）通量的积累，然后由交换不稳定性调节。在这里，我们建议，而不是它主要是一个动态的重要{ \it toroidal}字段-发电机动作的结果，触发的显着，但仍然相对较弱的垂直场-定义和调节属性的MAD。我们建议，快速对流样的不稳定性，涉及交换的环形通量管和操作同时与磁旋转不稳定性（MRI），可以调节光盘的结构和逃逸的净通量。我们概括的对流稳定性标准和光盘结构方程，包括一个强大的环形场的影响，并表明对流流动可以被驱动到两个不同的边缘稳定的状态，其中之一，我们与MAD。我们确认我们的理论模型的可扩展性，通过比较其定量预测模拟的MAD和SANE（强磁化，但不是“逮捕”）光盘，并提出了一套标准，可以帮助区分MAD从其他吸积状态。与文献中先前的说法相反，我们认为MRI在MAD中不受抑制，并且可能是强环向场存在的原因。
英文摘要：
Magnetically arrested accretion discs (MADs) around black holes (BH) have the potential to stimulate the production of powerful jets and account for recent ultra-high-resolution observations of BH environments. Their main properties are usually attributed to the accumulation of dynamically significant net magnetic (vertical) flux throughout the arrested region, which is then regulated by interchange instabilities. Here we propose instead that it is mainly a dynamically important {\it toroidal} field -- the result of dynamo action triggered by the significant but still relatively weak vertical field -- that defines and regulates the properties of MADs. We suggest that rapid convection-like instabilities, involving interchange of toroidal flux tubes and operating concurrently with the magnetorotatonal instability (MRI), can regulate the structure of the disc and the escape of net flux. We generalize the convective stability criteria and disc structure equations to include the effects of a strong toroidal field and show that convective flows could be driven towards two distinct marginally stable states, one of which we associate with MADs. We confirm the plausibility of our theoretical model by comparing its quantitative predictions to simulations of both MAD and SANE (strongly magnetized but not "arrested") discs, and suggest a set of criteria that could help to distinguish MADs from other accretion states. Contrary to previous claims in the literature, we argue that MRI is not suppressed in MADs and is probably responsible for the existence of the strong toroidal field.
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