The remarkable results by the Event Horizon Telescope collaboration concerning the emission from M87* and, more recently, its polarization properties, require an increasingly accurate modeling of the plasma flows around the accreting black hole. Radiatively inefficient sources such as M87* and Sgr A* are typically modeled with the SANE (standard and normal evolution) paradigm, if the accretion dynamics is smooth, or with the MAD (magnetically arrested disk) paradigm, if the black hole’s magnetosphere reacts by halting the accretion sporadically, resulting in a highly dynamical process. While the recent polarization studies seem to favor MAD models, this may not be true for all sources, and SANE accretion surely still deserves attention. In this work, we investigate the possibility of reaching the typical degree of magnetization and other accretion properties expected for SANE disks by resorting to the mean-field dynamo process in axisymmetric GRMHD simulations, which are supposed to mimic the amplifying action of an unresolved magnetorotational instability-driven turbulence. We show that it is possible to reproduce the main diagnostics present in the literature by starting from very unfavorable initial configurations, such as a purely toroidal magnetic field with negligible magnetization.

中文翻译：

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厚吸积盘的 GRMHD 平均场发电机模型是否健全？

事件视界望远镜合作在 M87* 发射以及最近它的偏振特性方面取得的显著成果，需要对吸积黑洞周围的等离子体流进行越来越准确的建模。M87* 和 Sgr A* 等辐射低效源通常使用 SANE（标准和正常演化）范式建模，如果吸积动力学是平滑的，或者使用 MAD（磁滞盘）范式建模，如果黑洞的磁层反应为偶尔停止吸积，导致高度动态的过程。虽然最近的极化研究似乎有利于 MAD 模型，但这可能不适用于所有来源，并且 SANE 吸积肯定仍然值得关注。在这项工作中，我们通过在轴对称 GRMHD 模拟中采用平均场发电机过程来研究达到 SANE 盘预期的典型磁化程度和其他吸积特性的可能性，该过程应该模拟未解决的磁旋转不稳定性驱动的湍流的放大作用。我们表明，通过从非常不利的初始配置（例如磁化强度可忽略不计的纯环形磁场）开始，可以重现文献中存在的主要诊断结果。