发表机构
Millennium Nucleus on Transversal Research and Technology to Explore Supermassive Black Holes (TITANS); Departamento de Ciencias, Facultad de Artes Liberales, Universidad Adolfo Ibáñez; Departamento de Física, Facultad de Ciencias Físicas y Matemáticas, Universidad de Chile（探索超大质量黑洞的横向研究与技术千年核; 阿道夫·伊巴涅斯大学自由艺术学院科学系; 智利大学物理与数学科学学院物理系）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
本研究通过二维粒子模拟识别了分层MRI湍流中粒子加速的三个阶段（重联注入、一阶费米加速、二阶费米与剪切加速），解释了最大能量与尺度分离比成正比的原因，并表明MRI可在低光度盘中产生超相对论粒子。
AI 中文摘要
围绕黑洞的低光度吸积盘是弱碰撞的，这有可能实现非热粒子加速。Sandoval等人（2024年；以下简称S24）对电子-正电子等离子体中分层磁旋转不稳定性（MRI）进行的局部二维粒子模拟揭示了非热粒子群，其最大能量与尺度分离比 $\omega_{c,0}/\Omega_0$ 成正比，其中 $\omega_{c,0}$ 和 $\Omega_0$ 分别是初始粒子回旋频率和开普勒频率。我们识别了所涉及的加速机制，并量化了它们对尺度分离的依赖性。加速主要发生在与MRI发电机相关的大尺度电流片内。粒子最初由磁岛分裂驱动的重联过程中的非理想电场注入，获得的能量与尺度分离无关。随后，它们在新形成并分离的磁岛之间的汇聚流中经历快速的一阶费米类加速。在此阶段，能量增长率与瞬时非相对论回旋频率成正比，与 $\omega_{c,0}/\Omega_0$ 无关。这种快速加速率意味着最大能量与 $\omega_{c,0}/\Omega_0$ 成正比。随后，粒子继续与磁岛反复相互作用，经历较慢的、主要属于二阶费米的加速，并有剪切加速的次要贡献。此阶段在几个轨道周期内仅将粒子能量增加几倍，与 $\omega_{c,0}/\Omega_0$ 无关。这三个阶段的组合意味着最大能量与 $\omega_{c,0}/\Omega_0$ 成正比，这解释了S24发现的标度关系，并表明MRI可能在低光度吸积盘中将粒子加速到超相对论能量。在三维空间中检验这些结果仍是重要的下一步。
英文摘要
Low-luminosity accretion disks around black holes are weakly collisional, potentially enabling nonthermal particle acceleration. Local two-dimensional particle-in-cell simulations of the stratified magnetorotational instability (MRI) in pair plasmas by Sandoval et al. (2024; hereafter S24) revealed nonthermal populations with maximum energies proportional to the scale-separation ratio $ω_{c,0}/Ω_0$, where $ω_{c,0}$ and $Ω_0$ are the initial particle cyclotron and Keplerian frequencies, respectively. We identify the acceleration mechanisms involved and quantify their scale-separation dependence. Acceleration occurs primarily within large-scale current sheets associated with an MRI dynamo. Particles are initially injected by non-ideal electric fields during reconnection driven by plasmoid splitting, attaining energies independently of scale separation. They subsequently undergo rapid first-order Fermi-like acceleration occurring within converging flows between newly formed, separating plasmoids. During this stage, energies grow at a rate proportional to the instantaneous non-relativistic cyclotron frequency, independently of $ω_{c,0}/Ω_0$. This fast acceleration rate implies a maximum energy proportional to $ω_{c,0}/Ω_0$. Particles then continue interacting repeatedly with plasmoids, undergoing slower, predominantly second-order Fermi acceleration, with a subdominant contribution from shear acceleration. This stage increases particle energies by only a factor of {\it a few} over several orbits, regardless of $ω_{c,0}/Ω_0$. The combination of these three stages implies a maximum energy proportional to $ω_{c,0}/Ω_0$, explaining the scaling found by S24 and suggesting that the MRI may accelerate particles to ultrarelativistic energies in low-luminosity disks. Testing these results in three dimensions remains an important next step.
