By means of simple dynamical experiments we study the combined effect of gravitational and gas dynamics in the evolution of an initially out-of-equilibrium, uniform, and rotating massive overdensity thought of as in isolation. The rapid variation of the system mean-field potential makes the pointlike particles (PPs), which interact only via Newtonian gravity, form a quasistationary thick disk dominated by rotational motions surrounded by far out-of-equilibrium spiral arms. On the other side, the gas component is subjected to compression shocks and radiative cooling so as to develop a much flatter disk, where rotational motions are coherent and the velocity dispersion is smaller than that of PPs. Around such gaseous disk long-lived, but nonstationary, spiral arms form: these are made of gaseous particles that move coherently because have acquired a specific phase-space correlation during the gravitational collapse phase. Such a phase-space correlation represents a signature of the violent origin of the arms and implies both the motion of matter and the transfer of energy. On larger scales, where the radial velocity component is significantly larger than the rotational one, the gas follows the same out-of-equilibrium spiral arms traced by PPs. We finally outline the astrophysical and cosmological implications of our results.

中文翻译：

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剧烈重力作用下形成具有长寿命螺旋臂的圆盘

通过简单的动力学实验，我们研究了重力和气体动力学在最初不平衡，均匀和旋转的大量过密度（被认为是孤立的）的演化过程中的综合作用。系统平均场电势的快速变化使仅通过牛顿重力相互作用的点状粒子（PPs）形成了准静态厚盘，该盘由旋转运动所包围，并被远不平衡的螺旋臂包围。另一方面，气体成分受到压缩冲击和辐射冷却，从而形成一个更加平坦的盘，在该盘上旋转运动是连贯的，并且速度分散度小于PPs。在这种气态磁盘周围，长寿但不稳定的螺旋臂形成了：它们是由气态粒子组成的，它们由于在重力塌陷阶段获得了特定的相空间相关性而相干运动。这种相空间相关性代表了手臂暴力起源的特征，并暗示了物质的运动和能量的传递。在更大的尺度上，径向速度分量明显大于旋转速度分量，气体遵循由PP追踪的相同的失衡螺旋臂。最后，我们概述了我们研究结果的天体物理学和宇宙学意义。在径向速度分量明显大于旋转速度分量的情况下，气体遵循由PP追踪的相同的失衡螺旋臂。最后，我们概述了我们研究结果的天体物理学和宇宙学意义。在径向速度分量明显大于旋转速度分量的情况下，气体遵循由PP追踪的相同的失衡螺旋臂。最后，我们概述了我们研究结果的天体物理学和宇宙学意义。