Radio observations of tidal disruption events (TDEs)—when a star is tidally disrupted by a supermassive black hole (SMBH)—provide a unique laboratory for studying outflows in the vicinity of SMBHs and their connection to accretion onto the supermassive black hole. Radio emission has been detected in only a handful of TDEs so far. Here we report the detection of delayed radio flares from an optically discovered TDE. Our prompt radio observations of the TDE ASASSN-15oi showed no radio emission until the detection of a flare six months later, followed by a second and brighter flare years later. We find that the standard scenario, in which an outflow is launched briefly after the stellar disruption, is unable to explain the combined temporal and spectral properties of the delayed flare. We suggest that the flare is due to the delayed ejection of an outflow, perhaps following a transition in accretion states. Our discovery motivates observations of TDEs at various timescales and highlights a need for new models.

潮汐干扰事件 (TDE) 的无线电观测——当一颗恒星被超大质量黑洞 (SMBH) 潮汐干扰时——提供了一个独特的实验室来研究 SMBH 附近的流出物及其与吸积到超大质量黑洞上的联系。到目前为止，仅在少数 TDE 中检测到了无线电发射。在这里，我们报告了从光学发现的 TDE 中检测到延迟射电耀斑。我们对 TDE ASASSN-15oi 的快速射电观测显示，直到六个月后检测到耀斑，并在几年后第二次更亮的耀斑出现之前，没有无线电发射。我们发现标准场景，即恒星中断后短暂启动外流，无法解释延迟耀斑的组合时间和光谱特性。我们认为耀斑是由于流出物的延迟喷射，可能是在吸积状态的转变之后。我们的发现激发了在不同时间尺度上对 TDE 的观察，并强调了对新模型的需求。