天文学家分析引力波事件GW190412，发现一颗新形成的黑洞以约112,000英里/小时（180,000公里/小时）速度从诞生地点被反冲推出，约等于620英里/秒。研究首次同时恢复了该黑洞的速度和空间方向，形成完整的“反冲”运动图像。该事件来自两个质量明显不等的黑洞合并，全球引力波探测网络记录了其信号。关键物理机制是引力波辐射不对称：当动量更多地向一个方向辐射时，合并后的黑洞会被推向相反方向。
研究团队利用信号中的高阶模式，即比主要四极信号更弱的附加波形结构。这些成分会随观测角度变化，因此可以推断残余黑洞相对于地球的运动方向。研究还结合轨道角动量方向（垂直于轨道平面的轴）来确定反冲与系统几何的对齐关系，从而将原本复杂的“啁啾”信号转化为三维运动轨迹。GW190412的质量不对称增强了这些弱模式，使方向测量成为可能。
测得的反冲速度超过31英里/秒（50公里/秒），这一阈值足以使黑洞逃离致密恒星环境，例如典型逃逸速度低于该值的球状星团。这意味着被“踢出”的黑洞可能离开其诞生环境，从而减少后续重复合并的概率。若反冲路径穿过稀薄气体，电磁辐射信号可能较弱；若穿过致密物质，则可能短暂发光，例如在活动星系核盘中。自2015年首次引力波探测以来，多个黑洞并合事件已被记录；随着探测器灵敏度提高，未来更多具有高阶模式的不对称并合将帮助绘制黑洞残骸在宇宙中的运动分布。
Astronomers analyzed the gravitational-wave event GW190412 and found that a newly formed black hole was recoiled from its birth site at about 112,000 miles per hour (180,000 kilometers per hour), roughly 620 miles per second. The study reconstructed both the speed and spatial direction of the object for the first time, producing a complete recoil motion portrait. The signal came from the merger of two black holes with strongly unequal masses detected by a global gravitational-wave network. The key mechanism is asymmetric gravitational-wave emission: when more momentum is radiated in one direction, the merged remnant is pushed in the opposite direction.
Researchers used higher-order modes in the signal, weaker waveform components beyond the dominant quadrupole emission. These components vary with viewing angle, allowing scientists to infer the remnant’s motion relative to Earth. The analysis also incorporated orbital angular momentum, the axis perpendicular to the orbital plane, to determine how the recoil aligned with the system geometry and to convert the complex chirp signal into a three-dimensional motion track. The strong mass asymmetry of GW190412 amplified these weaker modes and enabled the directional measurement.
The measured recoil exceeds 31 miles per second (50 kilometers per second), a threshold sufficient for a black hole to escape dense stellar environments such as globular clusters, whose escape speeds are typically lower. This implies that kicked remnants may leave their birth environments and cease further mergers there. If the recoil travels through thin gas the electromagnetic signature may be faint, while passage through dense material could produce brief brightening, for example within an active galactic nucleus disk. Since the first gravitational-wave detection in 2015, many black-hole mergers have been recorded, and improved detector sensitivity will allow future asymmetric events with higher-order modes to map the motion of black-hole remnants across the universe.