Gravitational interactions between the Large Magellanic Cloud (LMC) and the stellar and dark matter halo of the Milky Way are expected to give rise to disequilibrium phenomena in the outer Milky Way^{1,2,3,4,5,6,7}. A local wake is predicted to trail the orbit of the LMC, and a large-scale overdensity is predicted to exist across a large area of the northern Galactic hemisphere. Here we report the detection of both the local wake and northern overdensity (hereafter the ‘collective response’) in a map of the Galaxy based on 1,301 stars at Galactocentric distances between 60 and 100 kiloparsecs. The location of the wake is in good agreement with an N-body simulation that includes the dynamical effect of the LMC on the Milky Way halo. The density contrast of the wake and collective response are stronger in the data than in the simulation. The detection of a strong local wake is independent evidence that the Magellanic clouds are on their first orbit around the Milky Way. The wake traces the path of the LMC, which will provide insight into the orbit of the LMC, which in turn is a sensitive probe of the mass of the LMC and the Milky Way. These data demonstrate that the outer halo is not in dynamical equilibrium, as is often assumed. The morphology and strength of the wake could be used to test the nature of dark matter and gravity.

大麦哲伦星云 (LMC) 与银河系的恒星和暗物质晕之间的引力相互作用预计会在外银河^{1,2,3,4,5,6,7}中引起不平衡现象。预计局部尾流将跟随 LMC 的轨道，预计银河系北半球的大片区域将存在大规模的超密度。在这里，我们报告了基于 1,301 颗恒星在 60 到 100 千秒差距之间的银河中心距离的银河地图中检测到的局部尾流和北部超密度（以下称为“集体响应”）。尾迹的位置与N非常吻合- 天体模拟，包括 LMC 对银河系晕的动态影响。数据中尾流和集体响应的密度对比比模拟中的要强。检测到强烈的局部尾流是麦哲伦星云处于其围绕银河系的第一个轨道的独立证据。尾流追踪 LMC 的路径，这将提供对 LMC 轨道的洞察，这反过来又是 LMC 和银河系质量的敏感探测器。这些数据表明，外晕并不像通常假设的那样处于动态平衡。尾流的形态和强度可用于测试暗物质和重力的性质。