Recent observations have suggested that circumstellar disks may commonly form around young stellar objects. Although the formation of circumstellar disks can be a natural result of the conservation of angular momentum in the parent cloud, theoretical studies instead show disk formation to be difficult from dense molecular cores magnetized to a realistic level, owing to efficient magnetic braking that transports a large fraction of the angular momentum away from the circumstellar region. We review recent progress in the formation and early evolution of disks around young stellar objects of both low-mass and high-mass, with an emphasis on mechanisms that may bridge the gap between observation and theory, including non-ideal MHD effects and asymmetric perturbations in the collapsing core (e.g., magnetic field misalignment and turbulence). We also address the associated processes of outflow launching and the formation of multiple systems, and discuss possible implications in properties of protoplanetary disks.

中文翻译：

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年轻恒星周围盘的形成和演化

最近的观察表明，星周盘可能通常形成在年轻的恒星物体周围。虽然星周盘的形成可能是母云中角动量守恒的自然结果，但理论研究表明，从磁化到现实水平的致密分子核，盘形成是困难的，因为有效的磁制动可以传输大量远离星周区域的角动量的一部分。我们回顾了低质量和高质量年轻恒星物体周围盘的形成和早期演化的最新进展，重点是可能弥合观察和理论之间差距的机制，包括非理想的 MHD 效应和不对称扰动在坍塌的核心中（例如，磁场未对准和湍流）。