标题： 黑洞吸积的变异性：对旋转和磁场能量平衡的依赖 显示英文标题

标题： Variability in Black Hole Accretion: Dependence on Rotational and Magnetic Energy Balance

摘要： 大多数关于黑洞（BH）热吸积流的广义相对论磁流体动力学模拟都是以小旋转环状结构初始化，并产生只有小幅波动的稳定喷流。 然而，最近的研究使用更大尺度的Bondi类似初始条件报告了间歇性的喷流活动和有序旋转的丧失。 为了研究这些差异，我们在四个黑洞自旋下修改了标准环状结构：$a_*=0$，$0.5$，$0.9$，$-0.9$。 首先，我们显著增加了环状结构的大小（压力最大值在500个引力半径处），使得可以在没有气体耗尽的情况下进行长时间模拟（$2.8\times10^5$个引力时间）。 这些模拟再现了在较小环状结构中观察到的弱变异性，表明仅更大的动态范围不会导致强烈的波动。 我们观察到，与$a_*=0$相比，BH 自转速度为$a_*=0.5,~0.9$时，吸积率分别被抑制了$\sim 1.6, ~2.5$倍。 此外，密度分布对于顺行 BH 来说，其比例为$\rho(r)\propto r^{-1.1}$。 接下来，我们通过设置等离子体-$\beta\approx 1$，显著增强了大环状物中的初始磁场。 这引起了演化的强烈变化。 例如，在$a_*=0.9$模型中，喷流效率现在变化超过3个数量级，气体旋转方向也发生了反转。 结合这些结果与先前的研究，我们认为一个关键参数是初始状态下旋转能与磁能的比值$R$。 模型中$R$值较大的模型在后期表现出更强的变异性。 其含义是，所有模拟，以及更广泛地说，自然界中的所有热吸积流，如果演化足够长的时间，最终都会发展出间歇性喷流。 显示英文摘要

摘要： Most general relativistic magnetohydrodynamic simulations of black hole (BH) hot accretion flows are initialized with small rotating tori and produce stable jets with only small fluctuations. However, recent studies using larger scale Bondi-like initial conditions have reported intermittent jet activity and loss of coherent rotation. To investigate the differences, we modify the standard torus setup across four BH spins: $a_*=0$, $0.5$, $0.9$, $-0.9$. First, we increase the torus size significantly (pressure maximum at 500 gravitational radii), allowing long simulations ($2.8\times10^5$ gravitational times) without gas depletion. These runs reproduce the weak variability seen in smaller tori, indicating that a larger dynamic range alone does not cause strong fluctuations. We observe moderate suppression of the accretion rate by factors of $\sim 1.6, ~2.5$ for BH spins $a_*=0.5,~0.9$, respectively, compared to $a_*=0$. Also, the density profile scales as $\rho(r)\propto r^{-1.1}$ for prograde BHs. Next, we considerably strengthen the initial magnetic field in the large torus by setting the plasma-$\beta\approx 1$. This induces strong variability in the evolution. The jet efficiency in the $a_*=0.9$ model, for instance, now varies by over 3 orders of magnitude, and gas rotation reverses directions. Combining these results with prior studies, we propose that a key parameter is the ratio $R$ between the rotational and magnetic energies in the initial state. Strong variability appears later in models with a larger value of $R$. The implication is that all simulations, and by extension all hot accretion flows in Nature, will ultimately develop intermittent jets if evolved long enough.