论文标题
由于流宇宙射线，银河系簇中的新浮力不稳定
A new buoyancy instability in galaxy clusters due to streaming cosmic rays
论文作者
论文摘要
据信活动的银河核（AGN）提供了防止星系簇核心中气体冷却的能量。但是，如何在整个群内培养基（ICM）中运输和热效应该能量尚不清楚。在最近的工作中，我们表明流媒体宇宙射线（CRS）在稀释的ICM等离子体中破坏了声波。在这里，我们表明在存在重力的情况下，CR流也破坏了压力平衡的波。我们称这种新的不稳定浮力不稳定（CRBI）。与没有CRS的标准结果形成鲜明对比的是，由于CR流的短波长，压力平衡模式高度可压缩。最大增长率是$（p_c/p_g）β{1/2}ω_ {\ rm ff} $，其中$ p_c/p_g $是CR压力与热气压的比例，$β$是热力与磁压力和$ω__{\ rm ff ff fff的比率。 CRBI与背景热通量驱动的浮力不稳定性（即热频率驱动的浮力不稳定性（HBI）和磁性热不稳定性（MTI）一起运行。当热均值自由路径$ l _ {\ rm Mfp} $是$ \ ll $ The Gas Scale Height $ H $时，HBI/MTI设定了大尺度的增长率，而CRBI则在小规模上设定了增长率。相反，当$ l _ {\ rm Mfp} \ sim H $和$（p_c/p_g）β^{1/2} \ gtrsim 1 $ 1 $时，CRBI增长率超过HBI/MTI增长率，即使在大尺度上也是如此。我们的结果表明，CR驱动的不稳定性可能部分负责星系簇中观察到的声波/弱冲击和湍流。在无线电泡沫附近产生的CR驱动不稳定性也可能在整个集群中重新分布AGN能量。
Active Galactic Nuclei (AGN) are believed to provide the energy that prevents runaway cooling of gas in the cores of galaxy clusters. However, how this energy is transported and thermalized throughout the Intracluster Medium (ICM) remains unclear. In recent work we showed that streaming cosmic rays (CRs) destabilise sound waves in dilute ICM plasmas. Here we show that CR streaming in the presence of gravity also destabilises a pressure-balanced wave. We term this new instability the CR buoyancy instability (CRBI). In stark contrast to standard results without CRs, the pressure-balanced mode is highly compressible at short wavelengths due to CR streaming. Maximal growth rates are of order $(p_c / p_g) β^{1/2} ω_{\rm ff}$, where $p_c/p_g$ is the ratio of CR pressure to thermal gas pressure, $β$ is the ratio of thermal to magnetic pressure and $ω_{\rm ff}$ is the free-fall frequency. The CRBI operates alongside buoyancy instabilities driven by background heat fluxes, i.e. the heat-flux-driven buoyancy instability (HBI) and the magneto-thermal instability (MTI). When the thermal mean free path $l_{\rm mfp}$ is $\ll$ the gas scale height $H$, the HBI/MTI set the growth rate on large scales, while the CRBI sets the growth rate on small scales. Conversely, when $l_{\rm mfp} \sim H$ and $(p_c/p_g) β^{1/2} \gtrsim 1$, CRBI growth rates exceed HBI/MTI growth rates even on large scales. Our results suggest that CR-driven instabilities may be partially responsible for the sound waves/weak shocks and turbulence observed in galaxy clusters. CR-driven instabilities generated near radio bubbles may also play an important role redistributing AGN energy throughout clusters.
