Gravitational torque in circumbinary discs: global radial oscillations
Gravitational torque in circumbinary discs: global radial oscillations
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环双星盘中的重力扭矩：全局径向振荡
DOI：
10.1093/mnras/stae134
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发表时间：
2024
影响因子：
4.8
通讯作者：
Cimerman N
中科院分区：
文献类型：
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作者：
Cimerman N
环双星盘（CBD）出现在许多天体物理环境中，包括年轻的恒星双星和超大质量黑洞双星。它们的结构是由中心双星施加在圆盘上的引力力矩调节的。已知CBD中的二进制扭矩密度（所谓的激励扭矩密度）的空间分布具有全局大振幅、准周期振荡的特征，这通常被解释为局部共振Lindblad扭矩。在这里，我们调查这些扭矩振荡的性质，使用2D，无粘流体动力学模拟和理论计算。我们发现，扭矩振荡出现由于重力耦合的二进制潜在的密度波发射附近的内腔和自由传播的光盘。我们提供的扭矩密度振荡的径向周期性的分析预测，并验证它们与模拟，显示盘声速和密度波螺旋臂的多重性是设置的振荡的径向结构的关键因素。共振Lindblad扭矩在确定扭矩振荡的径向结构和周期性方面没有直接作用，并且仅通过驱动圆盘中的密度波来表现自己。我们还观察到在盘的内边缘处的旋涡的形成，这可以提供对CBD中的角动量输运的非平凡贡献，并且可能参与非轴对称中心腔的发展。
Circumbinary discs (CBDs) arise in many astrophysical settings, including young stellar binaries and supermassive black hole binaries. Their structure is mediated by gravitational torques exerted on the disc by the central binary. The spatial distribution of the binary torque density (so-called excitation torque density) in CBDs is known to feature global large-amplitude, quasi-periodic oscillations, which are often interpreted in terms of the local resonant Lindblad torques. Here, we investigate the nature of these torque oscillations using 2D, inviscid hydrodynamic simulations and theoretical calculations. We show that torque oscillations arise due to the gravitational coupling of the binary potential to the density waves launched near the inner cavity and freely propagating out in the disc. We provide analytical predictions for the radial periodicity of the torque density oscillations and verify them with simulations, showing that disc sound speed and the multiplicity of the density wave spiral arms are the key factors setting the radial structure of the oscillations. Resonant Lindblad torques play no direct role in determining the radial structure and periodicity of the torque oscillations and manifest themselves only by driving the density waves in the disc. We also observe the formation of vortices at the inner edge of the disc, which can provide a non-trivial contribution to the angular momentum transport in the CBD and may be involved in the development of a non-axisymmetric central cavity.