Accelerating AGN jets to parsec scales using general relativistic MHD simulations
Accelerating AGN jets to parsec scales using general relativistic MHD simulations
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DOI：
10.1093/mnras/stz2626
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发表时间：
2019-04
影响因子：
4.8
通讯作者：
K. Chatterjee;M. Liska;A. Tchekhovskoy;S. Markoff
中科院分区：
文献类型：
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作者：
K. Chatterjee;M. Liska;A. Tchekhovskoy;S. Markoff
吸积的黑洞会产生准直的流出物或喷流，它们在距离上跨越许多数量级，加速到相对论速度，并准直到狭窄的开口角度。其中，可能最不为人所知的是由于与周围介质相互作用而产生的射流准直。为了研究这种相互作用，我们以前所未有的分辨率对一个大吸积盘产生的射流进行了轴对称广义相对论磁流体动力学模拟，在时间和距离上跨越了5个数量级。在这种圆盘的支持下，喷流呈抛物线状，类似于M87星系喷流，洛伦兹系数与喷流半开口角γθ≪1的结果类似于对活动星系核（agn）喷流的甚长基线干涉测量法（VLBI）观测所得的值；这提示agn的椎间盘延长。我们发现射流与周围介质之间的相互作用导致了夹点不稳定性的发展，这通过将磁场和动能转化为热量而在整个射流中产生显著的径向和横向变化。因此，射流中的压缩区域可以作为辐射热点被探测到，并可能为粒子加速提供理想的场所。挤压还会导致来自周围介质的气体在射流的磁场线之间受到挤压，导致质量负荷增加，并使射流减速至非相对论速度，这可能会导致AGN流出物中观察到的脊鞘结构。
Accreting black holes produce collimated outflows, or jets, that traverse many orders of magnitude in distance, accelerate to relativistic velocities, and collimate into tight opening angles. Of these, perhaps the least understood is jet collimation due to the interaction with the ambient medium. In order to investigate this interaction, we carried out axisymmetric general relativistic magnetohydrodynamic simulations of jets produced by a large accretion disc, spanning over 5 orders of magnitude in time and distance, at an unprecedented resolution. Supported by such a disc, the jet attains a parabolic shape, similar to the M87 galaxy jet, and the product of the Lorentz factor and the jet half-opening angle, γθ ≪ 1, similar to values found from very long baseline interferometry (VLBI) observations of active galactic nuclei (AGNs) jets; this suggests extended discs in AGNs. We find that the interaction between the jet and the ambient medium leads to the development of pinch instabilities, which produce significant radial and lateral variability across the jet by converting magnetic and kinetic energy into heat. Thus pinched regions in the jet can be detectable as radiating hotspots and may provide an ideal site for particle acceleration. Pinching also causes gas from the ambient medium to become squeezed between magnetic field lines in the jet, leading to enhanced mass loading and deceleration of the jet to non-relativistic speeds, potentially contributing to the spine-sheath structure observed in AGN outflows.