We present the numerical study of the formation of spiral structure in the context of violent relaxation. Initial conditions are the out-of-equilibrium disks of self-gravitating particles in rigid rotation. By that mechanism, robust and non-stationary spiral arms can be formed within a few free-fall times by the shearing of the mass ejection following the collapse. With a closer look, we find different properties of the arms in connection with the initial configuration. The winding degree tends to increase with initial angular speed provided that a disk is thin. If disk surface is circular, both number and position of arms are governed by the Poissonian density fluctuations that produce more arms as more particles are introduced. On the contrary, if the surface ellipticity is imposed, the number of arms and their placement are effectively controlled. Otherwise, the increase of thickness leads to a complicated outcome since the number of arms and winding degree are less effectively controlled. We speculate that this complexity is caused by a strong non-axisymmetric field during the violent relaxation that disorganizes the pre-collapse motion and the concentration of particles.

中文翻译：

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自引力盘剧烈弛豫形成螺旋结构

我们提出了在剧烈松弛的背景下螺旋结构形成的数值研究。初始条件是刚性旋转的自引力粒子的不平衡圆盘。通过这种机制，通过坍缩后的物质抛射的剪切，可以在几个自由落体时间内形成坚固且非静止的螺旋臂。仔细观察，我们发现与初始配置相关的臂的不同属性。如果圆盘较薄，则缠绕程度会随着初始角速度增加而增加。如果磁盘表面是圆形，则臂的数量和位置都受泊松密度波动的控制，随着更多粒子的引入，会产生更多的臂。相反，如果施加表面椭圆度，则 武器的数量和放置得到有效控制。否则，增加厚度会导致复杂的结果，因为臂的数量和缠绕度的控制效果较差。我们推测，这种复杂性是由剧烈弛豫过程中强烈的非轴对称场引起的，这种场扰乱了预坍缩运动和粒子的浓度。