Close encounters between young stellar objects in star-forming clusters are expected to markedly perturb circumstellar disks. Such events are witnessed in numerical simulations of star formation^1,2,3, but few direct observations of ongoing encounters have been made. Here we report sub-0.1″-resolution Atacama Large Millimeter/Submillimeter Array and Jansky Very Large Array observations towards the million-year-old binary protostar Z Canis Majoris in dust continuum and molecular line emission. A point source ~4,700 au from the binary has been discovered at both millimetre and centimetre wavelengths. It is located along the extension of a ~2,000 au streamer structure previously found in scattered light imaging, whose counterpart in dust and gas emission is also newly identified. Comparison with simulations shows signposts of a rare flyby event in action. Z CMa is a ‘double burster’, as both binary components undergo accretion outbursts⁴, which may be facilitated by perturbations to the host disk by flybys^5,6,7,8.

恒星形成星团中年轻恒星物体之间的近距离接触预计会显着扰乱星周盘。在恒星形成的数值模拟中见证了此类事件^1,2,3，但很少对正在进行的遭遇进行直接观察。在这里，我们报告了亚 0.1 英寸分辨率的 Atacama 大毫米/亚毫米阵列和 Jansky 甚大阵列对具有百万年历史的双原星 Z Canis Majoris 在尘埃连续体和分子线发射中的观测。在毫米和厘米波长处都发现了二进制文件中约 4,700 au 的点源。它位于先前在散射光成像中发现的约 2,000 au 流光结构的延伸部分，其在尘埃和气体排放中的对应物也被新发现。与模拟的比较显示了正在发生的罕见飞越事件的路标。Z CMa 是一个“双爆发”，因为两个双星分量都经历吸积爆发⁴，这可能是由飞掠对主磁盘的扰动促进的^5,6,7,8。