The Gravitational Instability of Adiabatic Filaments
The Gravitational Instability of Adiabatic Filaments
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DOI：
10.3847/1538-4365/ab77c2
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发表时间：
2020-02
期刊：
影响因子：
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通讯作者：
E. Coughlin;C. Nixon
中科院分区：
文献类型：
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作者：
E. Coughlin;C. Nixon
丝状结构，或狭长的物质流，出现在天文学的许多领域。在这里，我们调查的稳定性，这样的细丝进行本征模分析的绝热和多变的流体圆柱体，这是圆柱形模拟的球形多面体。我们表明，这些气缸是重力不稳定的扰动沿着轴的圆柱低于临界波数kcrit的几个，其中kcrit是相对于圆柱体的半径测量。在这个临界波数以下，扰动增长为，其中τ是相对于穿过圆柱体直径的声音穿越时间的时间，并且我们导出增长率σu作为波数的函数。我们发现在特定的波数kmax <$1处存在最大的增长率σmax <$1，并且我们导出了在一定绝热指数范围内的增长率σmax和波数kmax和kcrit。在某种程度上，纤维结构可以近似为绝热和流体状，我们的结果意味着这些细丝是不稳定的，而不需要呼吁磁场或外部介质。此外，从这种细丝的不稳定性中凝结出来的物体通过优选的长度尺度分离，在优选的时间尺度上形成，并且具有优选的质量尺度。
Filamentary structures, or long and narrow streams of material, arise in many areas of astronomy. Here we investigate the stability of such filaments by performing an eigenmode analysis of adiabatic and polytropic fluid cylinders, which are the cylindrical analog of spherical polytropes. We show that these cylinders are gravitationally unstable to perturbations along the axis of the cylinder below a critical wavenumber kcrit ≃ few, where kcrit is measured relative to the radius of the cylinder. Below this critical wavenumber, perturbations grow as , where τ is time relative to the sound-crossing time across the diameter of the cylinder, and we derive the growth rate σu as a function of wavenumber. We find that there is a maximum growth rate σmax ∼ 1 that occurs at a specific wavenumber kmax ∼ 1, and we derive the growth rate σmax and the wavenumbers kmax and kcrit for a range of adiabatic indices. To the extent that filamentary structures can be approximated as adiabatic and fluidlike, our results imply that these filaments are unstable without the need to appeal to magnetic fields or external media. Further, the objects that condense out of the instability of such filaments are separated by a preferred length scale, form over a preferred timescale, and possess a preferred mass scale.