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arXiv 2603.08296astro-ph.HEphysics.plasm-ph
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压缩驱动的磁性束缚盘中的动力学不稳定性

Compression-Driven Kinetic Instabilities in Magnetically Arrested Disks

University of Illinois(伊利诺伊大学);Illinois Center for Advanced Study of the Universe(伊利诺伊大学宇宙高级研究中心);Columbia University(哥伦比亚大学);Center for Computational Astrophysics, Flatiron Institute(平顿研究所计算天体物理中心);Princeton University(普林斯顿大学);University of Wisconsin–Madison(威斯康星大学麦迪逊分校)

Vedant Dhruv, Lorenzo Sironi, Jordy Davelaar, Aaron Tran

AI总结:

研究通过二维粒子-细胞模拟,探讨压缩驱动磁性束缚盘中电子-离子等离子体的各向异性不稳定性,揭示其与热能、温度比及压缩率的关系,为黑洞吸积模型提供依据。

摘要:

事件视界尺度的低亮度黑洞吸积流观测倾向于磁性束缚盘,其特征是动态重要的磁场(β≈1,其中β是等离子体热压与磁压的比值)和双温度的跨相对论等离子体。受同步辐射发射区域的等离子体条件启发,我们进行了电子-离子等离子体的二维粒子-细胞模拟,该模拟考虑了现实的质子质量比,并受到持续垂直于平均磁场B₀的压缩作用。粒子磁矩的守恒驱动压力各向异性P⊥>P∥,触发各向异性驱动的不稳定性。对于离子等离子体βi0=0.5和离子温度kBTi0/mi c²=0.05,离子压力各向异性由离子旋磁不稳定性调节,而镜模影响晚期电子各向异性。两种物种在高能级发展出非热成分,与旋磁尺度波动引起的随机加速一致。我们描述了等离子体不稳定性出现和时间演化的特征,以及由此产生的离子和电子各向异性及能量谱如何随βi0、kBTi0/mi c²、电子-离子温度比Te0/Ti0以及压缩率变化。增加热能向相对论值发展提高了所有观察到的不稳定性各向异性阈值,允许更大的各向异性发展。对于Te0/Ti0<1,如预期的无碰撞双温度吸积流,镜模和哨音不稳定性的发展被延迟或抑制,导致电子逐渐趋于绝热演化。我们的发现可用于指导黑洞吸积的全局流体模型。

英文摘要:

Event horizon-scale observations of low-luminosity black hole accretion flows favor magnetically arrested disks, characterized by dynamically important magnetic fields ($β\lesssim1$, where $β$ is the ratio of plasma thermal pressure to magnetic pressure) and a two-temperature transrelativistic plasma. Motivated by plasma conditions in the synchrotron-emitting regions of these models, we perform 2D particle-in-cell simulations of electron-ion plasmas with a realistic mass ratio, subject to continuous compression perpendicular to the mean magnetic field $\boldsymbol{B}_0$. Conservation of particle magnetic moments drives pressure anisotropy $P_{\perp}>P_{\parallel}$, triggering anisotropy-driven instabilities. For ion plasma beta $β_{i0}=0.5$ and ion temperature $k_{\text{B}}T_{i0}/m_i c^2=0.05$, the ion pressure anisotropy is regulated by the ion cyclotron instability, while the mirror mode influences the late-time electron anisotropy. Both species develop nonthermal components at high energies, consistent with stochastic acceleration by cyclotron-scale fluctuations. We characterize how the onset and time evolution of the plasma instabilities, as well as the resulting ion and electron anisotropies and energy spectra, vary with $β_{i0}$, $k_{\text{B}}T_{i0}/m_i c^2$, electron-to-ion temperature ratio $T_{e0}/T_{i0}$, and the compression rate. Increasing the thermal energy toward relativistic values raises the anisotropy thresholds for all instabilities observed in our simulations, allowing larger anisotropies to develop. For $T_{e0}/T_{i0}<1$, as expected in collisionless two-temperature accretion flows, the growth of mirror and whistler instabilities is delayed or suppressed, leading to increasingly adiabatic evolution of the electrons. Our findings can be used to inform global fluid models of black hole accretion.

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