Protostellar jets have a fundamental role at the earliest evolution of protostars of all masses. In the case of low-mass (≲8 M _⊙) protostars, strong observational evidence exists that the launching and collimation is due to the X- and/or disk-wind mechanisms. In these models, it is the protostar/disk system that creates all the necessary conditions to launch and collimate the jets near the protostar via strong magnetic fields. The origin of jets from more massive protostars has been investigated much less, in part because of the difficulty of resolving the collimation zone in these more distant objects. Here we present the highest angular resolution observations of a jet powered by a massive protostar, the Cep A HW2 radio jet. We imaged the radio emission at projected distances of only ∼20 au from the protostar, resolving the innermost 100 au of a massive protostellar jet for the first time. The morphology of the radio jet emission in this massive object is very different than what is usually observed in jets from low-mass protostars. We found that the outflowing material in HW2 has two components: a wide-angle wind launched from the protostar/disk system, and a highly collimated jet starting at 20–30 au from the protostar. We discuss two possible scenarios: an extension of the classical disk-wind to a massive protostar, or external collimation of a wide-angle wind. These results have important consequences for our understanding of how stars of different masses are formed.

原恒星喷流在所有质量的原恒星的最早演化过程中发挥着重要作用。在低质量的情况下（≲8 M _⊙) 原恒星，存在强有力的观测证据表明发射和准直是由于 X 和/或盘风机制。在这些模型中，原恒星/圆盘系统创造了所有必要条件，通过强磁场在原恒星附近发射和准直喷流。对更大质量的原恒星喷流起源的研究要少得多，部分原因是难以解析这些更远物体的准直区。在这里，我们展示了由大质量原恒星 Cep A HW2 射电喷气机提供动力的喷气机的最高角分辨率观测。我们在距原恒星仅约 20 天文单位的投影距离处对射电发射进行了成像，首次解析了大型原恒星喷流的最内部 100 天文单位。这个大质量天体的射电射流发射的形态与通常在低质量原恒星的射流中观察到的有很大不同。我们发现 HW2 中的流出物质有两个组成部分：从原恒星/圆盘系统发射的广角风，以及从原恒星 20-30 天文单位开始的高度准直射流。我们讨论了两种可能的情况：经典盘风向大质量原恒星的延伸，或广角风的外部准直。这些结果对于我们理解不同质量的恒星是如何形成的具有重要意义。我们讨论了两种可能的情况：经典盘风向大质量原恒星的延伸，或广角风的外部准直。这些结果对于我们理解不同质量的恒星是如何形成的具有重要意义。我们讨论了两种可能的情况：经典盘风向大质量原恒星的延伸，或广角风的外部准直。这些结果对于我们理解不同质量的恒星是如何形成的具有重要意义。