盘破裂与参数不稳定性在扭曲吸积盘中的表现
Disc breaking and parametric instability in warped accretion discs
AI总结：
研究通过高分辨率模拟揭示了扭曲吸积盘破裂的机制，发现大扭曲幅度下盘破裂形成环，而小幅度下则表现出参数不稳定性。
摘要：
我们首次进行了盘破裂/撕裂的局部模拟。扭曲可能由于盘与中心天体自转轴的不平行，或与二元系统（或行星）轨道平面的不平行而产生。扭曲的盘可以破裂成环，如观察到的环绕二元原行星盘和倾斜盘的全局模拟所示。在本工作中，我们通过高分辨率、近二维、局部（剪切箱）的水动力学模拟，隔离了盘破裂的机制。我们考虑了自由（非强迫）扭曲在波状（α < H/r）区域的演变。在较大的扭曲幅度（ψ_max ≳ 1）下，盘在约20个轨道时间尺度内破裂成四个环，环之间间隔约10H₀。扭曲表现出丰富的微小尺度动态，包括水平摇晃运动、垂直振荡或跳跃，扭曲变陡，以及冲击波。冲击波作为增强耗散的来源，促进间隙打开从而导致盘破裂。在较小的扭曲幅度（ψ_max ≲ 1）下，我们还发展了准线性理论，盘不破裂，而是表现出水动力学参数不稳定性。我们还研究了粘性的影响：在较小的扭曲幅度下，参数不稳定性被阻尼，扭曲以纯弯曲波传播，而在较大的扭曲幅度下，出现的间隙部分被粘性扩散填充。
英文摘要：
We present the first local simulations of disc breaking/tearing in a warped accretion disc. Warps can arise due to a misalignment between the disc and the rotation axis of the central object, or a misalignment with the orbital plane of a binary (or planetary) companion. Warped discs can break into rings, as found in observations of circumbinary protoplanetary discs and global simulations of tilted discs around spinning black holes. In this work we isolate the mechanism of disc breaking in high-resolution, quasi-2D, local (shearing box), hydrodynamic simulations of a Keplerian disc. We consider the evolution of a free (unforced) warp in the wavelike ($α< H/r$) regime. At large warp amplitudes ($ψ_{\text{max}} \gtrsim 1$) the disc breaks into four rings on timescales of around 20 orbits which are separated by gaps of around $\sim 10H_0$. The warp exhibits a rich tapestry of small-scale dynamics, including horizontal sloshing motions, vertical oscillations or bouncing, warp steepening, and shocks. The shocks act as a source of enhanced dissipation which facilitates gap opening and thus disc breaking. At smaller warp amplitudes $ψ_{\text{max}} \lesssim 1$, for which we also develop a quasi-linear theory, the disc does not break, but instead exhibits hydrodynamic parametric instability. We also investigate the effect of viscosity: at small warp amplitudes the parametric instability is damped and the warp propagates as a pure bending wave, while at large warp amplitudes the emerging gaps are partially filled by viscous diffusion.
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