致密天体吸积过程中相对论喷流的形成机制，是天体物理学的基础问题之一。理论上虽然很难回答这个问题，但对于 微类星体相对论喷流的观测，在现象上给出了规律：对于辐射出超软Ｘ射线的天体，相对论喷流是无法产生的。对于河外 星系M81中超软极亮X射线源(M81 ULS1)的光谱观测表明，蓝移的宽Hα发射线，是重子物质相对论喷流的证据。喷流的进 动导致发射线随时间变化，其投影速度约为光速的17%，这与微类星体的原型SS433极为相似。这种相对论喷流不可能起 源于白矮星，而是起源于中子星或黑洞，这与M81 ULS1的超软X射线光谱相矛盾。X射线超软源中相对论喷流的发现，打 破以往对喷流形成的理论认知。处在超爱丁顿吸积状态，并拥有光厚吸积盘外流的黑洞，可以用来解释这种超软谱态与相 对论喷流的共存现象。

The formation of relativistic jets by an accreting compact object is one of the fundamental mysteries of astrophysics. While the theory is poorly understood, the observations of relativistic jets from systems known as microquasars have led to a well-established phenomenology. Relativistic jets are not expected from sources with soft or supersoft X-ray spectra, although two such systems are known to produce relatively low-velocity bipolar out?ows. Here we report the optical spectra of an ultraluminous supersoft X-ray source (ULS) in the nearby galaxy M81 (M81 ULS-1) showing blueshifted broad Ha emission lines, the characteristics of baryonic jets with relativistic speeds. The time variable jets have projected velocities ~17 percent of the speed of light, which seems similar to those in the prototype microquasar SS433. Such relativistic jets are not expected to be launched from white dwarfs, but an origin from a black hole or neutron star in M81 ULS-1 is hard to reconcile with its constant soft X-rays. The completely unexpected presence of relativistic jets in a ULS challenges the canonical theories for jet formation, which is possibly explained by a long speculated supercritically accreting black hole with optically thick out?ows.