多尘埃粒子的流动不稳定性：I。线性增长的有利条件
Streaming Instability with Multiple Dust Species: I. Favourable Conditions for the Linear Growth
摘要：
最近的研究表明，流动不稳定性，驱动星子形成的主要机制之一，可能并不像以前认为的那样有效。在某些条件下，不稳定性的增长时间尺度可以比光盘寿命时，考虑多个尘埃物种。为了进一步探索这一发现，我们使用线性分析和直接数值模拟与气体流体和尘埃粒子相互验证和研究的不稳定模式的不稳定性更详细。我们将先前研究的参数空间扩展了一个数量级的范围内的粉尘粒度分布$[T_{s,min}, T_{s,max}]$和总的固体-气体质量比$\varepsilon$，并引入了第三维的大小分布的斜率$q$。我们发现，在$\varepsilon$ - $T_{s,max}$空间中，快速生长区和缓慢生长区明显分离，而这个边界对$q$或$T_{s,min}$并不敏感.随着广泛的尘埃尺寸存在于光盘（如$T_{s,min}\lesssim10^{-3}$），在缓慢增长制度的增长率下降，因为更多的尘埃物种被认为是。另一方面，对于窄范围的尘埃尺寸（例如$T_{s,max}/T_{s,min}=5$），在大多数$\varepsilon$ - $T_{s,max}$空间中的生长速率随着尘埃种类的增加而收敛，但是快速和缓慢生长状态保持明显分离。此外，它是不必要的，最大的尘埃物种主导的不稳定模式的增长，和较小的尘埃物种可以影响增长率在一个复杂的方式。在任何情况下，我们发现，快速增长的制度是由$\varepsilon\gtrsim 1$或$T_{s,max}\gtrsim 1$，这可能代表了星子形成的有利条件。
英文摘要：
Recent study suggests that the streaming instability, one of the leading mechanisms for driving the formation of planetesimals, may not be as efficient as previously thought. Under some disc conditions, the growth timescale of the instability can be longer than the disc lifetime when multiple dust species are considered. To further explore this finding, we use both linear analysis and direct numerical simulations with gas fluid and dust particles to mutually validate and study the unstable modes of the instability in more detail. We extend the previously studied parameter space by one order of magnitude in both the range of the dust-size distribution $[T_{s,min}, T_{s,max}]$ and the total solid-to-gas mass ratio $\varepsilon$ and introduce a third dimension with the slope $q$ of the size distribution. We find that the fast-growth regime and the slow-growth regime are distinctly separated in the $\varepsilon$-$T_{s,max}$ space, while this boundary is not appreciably sensitive to $q$ or $T_{s,min}$. With a wide range of dust sizes present in the disc (e.g. $T_{s,min}\lesssim10^{-3}$), the growth rate in the slow-growth regime decreases as more dust species are considered. With a narrow range of dust sizes (e.g. $T_{s,max}/T_{s,min}=5$), on the other hand, the growth rate in most of the $\varepsilon$-$T_{s,max}$ space is converged with increasing dust species, but the fast and the slow growth regimes remain clearly separated. Moreover, it is not necessary that the largest dust species dominate the growth of the unstable modes, and the smaller dust species can affect the growth rate in a complicated way. In any case, we find that the fast-growth regime is bounded by $\varepsilon\gtrsim 1$ or $T_{s,max}\gtrsim 1$, which may represent the favourable conditions for planetesimal formation.
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