Formation of dense gas cores in supernova remnant-cloud interactions

恒星的形成是在星际云中致密的、受重力约束的气体聚集体中发生的。这种恒星前的“核心”被认为是由重力和强会聚气流之间的非线性相互作用造成的，这些气流出现在一个由超新星爆炸等能量输入维持的湍流环境中。在这个项目中，研究了孤立的超新星遗迹与星际云的碰撞是否能够触发就地核形成这个理想化但基本的问题。为了实现这一目标，利用Nirvana仿真软件进行了基于最新数值计算、自适应网格加密和并行计算的高层数值模拟。我们的模型将磁流体力学与星际介质的自重、辐射冷却和各向异性热传导相结合。尽管缺乏非理想磁流体力学过程和详细的电离/化学等其他物理过程，但该方法意味着对当前激波-云相互作用模型的实质性改进。这方面的主要进展来自于并行泊松求解器的发展和各向异性热传导项的有效Stiff积分器的实现。Stiff传导积分器使得超新星残余膨胀的模型可以通过计算获得，因此允许超越通常采用的小云近似。通过在三维模拟中探索所有上述物理效应之间的复杂相互作用，该项目旨在解决以下关键问题：在什么条件下，在破碎的云被磁流体动力学不稳定性破坏之前，可以形成致密的气体核心。

Star formation takes place in dense, gravity-bound gas aggregations within interstellar clouds. Such pre-stellar 'cores' are believed to be created by the nonlinear interaction between gravity and strongly converging flows emerging in a turbulent environment sustained by energy input from e.g. supernova explosions. In this project, the idealized but fundamental problem is studied whether the collision of an isolated supernova remnant with an interstellar cloud is able to trigger in-situ core formation. In order to achieve this goal, high-level numerical modeling based on state-of-the-art numerics, adaptive mesh refinement and parallel computing is conducted using the NIRVANA simulation software. Our model couples magnetohydrodynamics with self-gravity, radiative cooling of the interstellar medium and anisotropic thermal conduction. Although lacking other physics like non-ideal magnetohydrodynamical processes and detailed ionisation/chemistry, the approach means a substantial improvement over current shock-cloud interaction models. Major progress in this respect stems from the development of a parallel Poisson solver and from the implementation of an efficient stiff integrator for the anisotropic thermal conduction term. The stiff integrator for conduction makes a modeling of the supernova remnant expansion computationally accessible and, hence, allows to go beyond the usually adopted small-cloud approximation.By exploring the complex interplay between all aforesaid physical effects in three-dimensional simulations the project aims to contribute to the key question under which conditions dense gas cores may be formed before the crushed cloud is disrupted by the action of magnetohydrodynamical instabilities.