星际壳层和超壳层包括eROSITA泡中的时间相关瑞利-泰勒不稳定性
The time-dependent Rayleigh-Taylor instability in interstellar shells and supershells, including the eROSITA bubbles
摘要：
瑞利-泰勒（RT）不稳定性在受到有效重力加速度的逆密度分层流体物理中是普遍存在的。在天体物理学中，由于强烈的时间依赖RT不稳定性，环境介质的陡峭分层可以更快地破碎气泡壳，导致经典的恒重力模型失效。我们推导出的时间相关的不稳定性标准分析的情况下，常数，指数，幂律加速度，通过高分辨率的数值模拟验证它们。结果表明：（1）即使在线性阶段，也存在一个与指数增长相反的项;（2）非线性增长渐近地接近Fermi和von Neumann的解;（3）相互贯穿的尖峰和气泡促进了显著的混合，界面的分形维数接近1.6，仅受数值扩散的限制，（4）在幂律加速和指数加速情况下，研究混合的被动标量的概率密度函数（PDF）变得越来越尖锐。应用我们的解决方案，恒星风气泡，年轻的超新星遗迹（SNRs），和超级气泡（SB），我们发现，RT不稳定性的增长率一般是较高的风吹气泡的外壳中的幂律分层介质比那些幂律上升的恒星机械光度，Tycho比Cas A-类SNRs，和单侧比对称SB。最近观察到的eROSITA气泡表明光滑的边缘表面，这意味着外壳没有受到RT不稳定性的影响。因此，气泡的动力学演化表明，最大的最终年龄明显高于其当前的年龄，我们估计约为2000万年。
英文摘要：
The Rayleigh-Taylor (RT) instability is omnipresent in the physics of inversely density-stratified fluids subject to effective gravitational acceleration. In astrophysics, a steep stratification of the ambient medium can fragment a bubble shell faster due to a strongly time-dependent RT instability, causing the classical constant gravity models to fail. We derive the time-dependent instability criteria analytically for the cases of constant, exponential, and power-law accelerations, verifying them through high-resolution numerical simulations. Our results show that (1) even in the linear phase there is a term opposing exponential growth, (2) non-linear growth approaches asymptotically the solution found by Fermi and von Neumann, (3) the interpenetrating spikes and bubbles promote a significant mixing, with the fractal dimension of the interface approaching 1.6, only limited by numerical diffusion, and (4) the probability density function (PDF) for the passive scalar to study mixing becomes increasingly sharper peaked for power-law and exponential acceleration. Applying our solutions to stellar wind bubbles, young supernova remnants (SNRs), and superbubbles (SBs), we find that the growth rate of the RT instability is generally higher in the shells of wind-blown bubbles in a power-law stratified medium than in those with power-law rising stellar mechanical luminosities, Tycho-like than Cas A-like SNRs, and one-sided than symmetric SBs. The recently observed eROSITA bubbles indicate smooth rim surfaces, implying that the outer shell has not been affected by RT instabilities. Therefore the dynamical evolution of the bubbles suggests maximum final ages that are significantly above their current age, which we estimate to be about 20 Myr.
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