Magnetohydrodynamic turbulence is a ubiquitous and fundamental ingredient underlying many astrophysical phenomena. The multiphase nature of the interstellar medium and the diversity of driving mechanisms give rise to spatial variation of turbulence properties, particularly plasma properties. There has been no observational diagnosis of the plasma modes beyond the solar system so far. Here we report the identification of different plasma modes in various Galactic environments, including active star-forming zones and supernova remnants, on the basis of our synchrotron polarization analysis. The observed high degree of consistency between the γ-ray excess in the Cygnus cocoon and the location of magnetosonic modes provides strong observational evidence for the long-advocated theory that magnetosonic modes dominate the cosmic ray (CR) scattering and acceleration. Our results open up a new avenue for the study of interstellar turbulence and demonstrate the indispensability of accounting for their plasma properties in all the relevant processes, including CR transport and star formation.

磁流体动力湍流是许多天体物理现象背后普遍存在的基本成分。星际介质的多相性质和驱动机制的多样性导致湍流特性，尤其是等离子体特性的空间变化。到目前为止，还没有对太阳系以外的等离子体模式进行观察诊断。在此，我们根据同步加速器极化分析报告了在各种银河环境中，包括活跃的恒星形成区和超新星残余物，对不同等离子体模式的识别。天鹅座茧中的γ射线过量与磁声模式位置之间观察到的高度一致性为长期主张的理论提供了有力的观察证据，即磁声模式主导宇宙射线（CR）的散射和加速。我们的研究结果为星际湍流的研究开辟了一条新途径，并证明了在所有相关过程（包括CR传输和恒星形成）中考虑其等离子体性质所必不可少的。