Ubiquitous instabilities of dust moving in magnetized gas
Ubiquitous instabilities of dust moving in magnetized gas
复制标题
磁化气体中灰尘运动普遍存在的不稳定性
DOI：
10.1093/mnras/sty1604
复制
发表时间：
2018
影响因子：
4.8
通讯作者：
J. Squire
中科院分区：
文献类型：
--
作者：
P. Hopkins;J. Squire
斯奎尔和霍普金斯的研究表明，耦合的尘埃-气体混合物通常会受到“共振阻力不稳定性”(RDI)的影响，这会导致两者之间的剧烈波动。但磁场和带电尘埃的作用尚未得到研究。因此，我们探索了气体中的RDI，它服从理想的MHD，并通过洛伦兹力和阻力与尘埃耦合，外部加速度(如重力、辐射)驱动尘埃在气体中漂移。我们表明，在所有波长和尘气比、漂移速度、尘埃电荷、‘停止时间’或阻力系数(对于任何阻力定律)或场强的非零值下，这总是不稳定的；而且，增长率仅弱地(次线性地)依赖于这些参数。尘埃电荷和磁场不会抑制不稳定性，但会产生大量新的不稳定“家族”，每个家族都有不同的行为。‘MHD波’(磁声或Alfven)RDI显示出沿‘共振’角的最大增长，其中模式的相速度与相应的MHD波相匹配，并且增长率随着波数的增加而无限制地增加。“陀螺”RDI是由漂移频率和Larmor频率之间的共振驱动的，使增长率在特定波长急剧达到峰值。其他不稳定性包括“声学”和“无压力”模式(以前研究过)，以及一个类似于宇宙射线不稳定性的家族，当洛伦兹力很强，尘埃沿着场线以超阿尔法速度流动时，就会出现宇宙射线不稳定性。我们讨论了在温暖的ISM、银河系周围介质/星系间介质(CGM/IGM)、H II区、SNE喷射物/残留物、日冕、冷星风、GMCS和活动星系核中的天体物理应用。
Squire & Hopkins showed that coupled dust–gas mixtures are generically subject to ‘resonant drag instabilities’ (RDIs), which drive violently growing fluctuations in both. But the role of magnetic fields and charged dust has not yet been studied. We therefore explore the RDI in gas that obeys ideal MHD and is coupled to dust via both Lorentz forces and drag, with an external acceleration (e.g. gravity, radiation) driving dust drift through gas. We show this is always unstable, at all wavelengths and non-zero values of dust-to-gas ratio, drift velocity, dust charge, ‘stopping time’ or drag coefficient (for any drag law), or field strength; moreover, growth rates depend only weakly (sub-linearly) on these parameters. Dust charge and magnetic fields do not suppress instabilities, but give rise to a large number of new instability ‘families,’ each with distinct behavior. The ‘MHD-wave’ (magnetosonic or Alfven) RDIs exhibit maximal growth along ‘resonant’ angles where the modes have a phase velocity matching the corresponding MHD wave, and growth rates increase without limit with wavenumber. The ‘gyro’ RDIs are driven by resonances between drift and Larmor frequencies, giving growth rates sharply peaked at specific wavelengths. Other instabilities include ‘acoustic’ and ‘pressure-free’ modes (previously studied), and a family akin to cosmic ray instabilities that appear when Lorentz forces are strong and dust streams super-Alfvenically along field lines. We discuss astrophysical applications in the warm ISM, circum-galactic medium/inter-galactic medium (CGM/IGM), H II regions, SNe ejecta/remnants, Solar corona, cool-star winds, GMCs, and AGN.
影响因子：
4.8
作者：
S. Walch;T. Naab
通讯作者：
S. Walch;T. Naab