关于银河系条状体屈曲不稳定性的性质

IF 5.8 2区 物理与天体物理 Q1 ASTRONOMY & ASTROPHYSICS
Ewa L. Łokas
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引用次数: 0

摘要

许多强大的模拟银条经历了屈曲不稳定性,表现为盘面垂直扭曲,随后消散。通过对一个孤立的类似银河系的星系的模拟,我证明了这种现象可以分为两个不同的阶段。在第一种情况下,畸变增大,其模速度保持与棒的模速度相等,因此畸变在棒的参考系中保持静止。这种增长可以用具有时相关力的驱动谐振子的机制来描述,它降低了恒星的垂直频率。在这一阶段结束时,大多数支撑条形轨道具有香蕉状形状,其共振垂直与水平频率比接近2。垂直振动幅值的增大导致水平振动幅值的减小和杆的收缩。质量重分布使谐振子产生绝热响应,提高了水平频率。在接下来的屈曲第二阶段,变形的模式速度增加,达到圆频率的三分之一,但随着半径的减小而减小。这种扭曲以一种运动弯曲波的形式传播并缠绕起来,留下一个明显的方形/花生形状。水平频率的增加导致棒材的减弱,香蕉状轨道转变为椒盐卷饼状轨道,但在棒材的外部,香蕉状轨道和扭曲仍然存在。结果强烈地表明,银河棒的屈曲与消防水带的不稳定性无关,但它可以用垂直共振的机制来充分解释,这种机制造成了后来的扭曲。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
On the nature of buckling instability in galactic bars
Many strong simulated galactic bars experience buckling instability, which manifests itself as a vertical distortion out of the disk plane, and later dissipates. Using a simulation of an isolated Milky Way-like galaxy, I demonstrate that the phenomenon can be divided into two distinct phases. In the first one, the distortion grows and its pattern speed remains equal to the pattern speed of the bar, so that the distortion remains stationary in the reference frame of the bar. The growth can be described with the mechanism of a driven harmonic oscillator with time-dependent force, which decreases the vertical frequencies of the stars. At the end of this phase, most bar-supporting orbits have banana-like shapes with a resonant vertical-to-horizontal frequency ratio close to two. The increase of amplitudes of vertical oscillations leads to the decrease of the amplitudes of horizontal oscillations and the shrinking of the bar. The mass redistribution causes the harmonic oscillators to respond adiabatically and increase the horizontal frequencies. In the following second phase of buckling, the pattern speed of the distortion increases – reaching one third of the circular frequency – but it decreases with radius. The distortion propagates as a kinematic bending wave and winds up, leaving behind a pronounced boxy/peanut shape. The increased horizontal frequencies cause the weakening of the bar and the transformation of banana-like orbits into pretzel-like ones, except in the outer part of the bar, where the banana-like orbits and the distortion survive. The results strongly suggest that the buckling of galactic bars is not related to the fire-hose instability, but it can be fully explained by the mechanism of vertical resonance creating the distortion that later winds up.
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来源期刊
Astronomy & Astrophysics
Astronomy & Astrophysics 地学天文-天文与天体物理
CiteScore
10.20
自引率
27.70%
发文量
2105
审稿时长
1-2 weeks
期刊介绍: Astronomy & Astrophysics is an international Journal that publishes papers on all aspects of astronomy and astrophysics (theoretical, observational, and instrumental) independently of the techniques used to obtain the results.
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