用光滑粒子流体动力学松弛原恒星吸积激波
Relaxation of protostellar accretion shocks using the smoothed particle hydrodynamics
摘要：
原恒星的吸积盘是由旋转核坍缩过程中的分子物质以近似弹道式的方式进入而形成的。这些下落物质的碰撞导致形成强烈的超音速激波，如果它们迅速冷却，就会导致这些物质在赤道平面上以薄结构的形式积累。本文利用光滑粒子流体力学（SPH）方法研究了原恒星吸积激波后气体的弛豫时间。为此，考虑了一维两分子片正面碰撞，模拟了激波后区域的温度和密度随时间的演化。结果表明，在强超声速激波中，激波后气体温度迅速升高，并随着冷却过程的进行而逐渐降低，与马赫数的平方成正比。适当的冷却函数表明，在适当的时间尺度下，碰撞中心（位于核的赤道面）转变为一个薄而致密的分子盘及其周围的原子和电离气体，这种吸积盘的结构可能为颗粒生长和原行星实体的形成提供了合适的条件。
英文摘要：
It is believed that protostellar accretion disks to be formed from nearly ballistic infall of the molecular matters in rotating core collapse. Collisions of these infalling matters lead to formation of strong supersonic shocks, which if they cool rapidly, result in accumulation of that material in a thin structure in the equatorial plane. Here, we investigate the relaxation time of the protostellar accretion post-shock gas using the smoothed particle hydrodynamics (SPH). For this purpose, a one-dimensional head-on collision of two molecular sheets is considered, and the time evolution of the temperature and density of the post-shock region simulated. The results show that in strong supersonic shocks, the temperature of the post-shock gas quickly increases proportional to square of the Mach number, and then gradually decreases according to the cooling processes. Using a suitable cooling function shows that in appropriate time-scale, the center of the collision, which is at the equatorial plane of the core, is converted to a thin dense molecular disk, together with atomic and ionized gases around it. This structure for accretion disks may justify the suitable conditions for grain growth and formation of proto-planetary entities.
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