Star Formation: Following the Evolutionary Sequence from Cloud Assembly through Protostars and Circumstellar Disks

我们银河系中大部分星星的形成都发生在巨大的分子云中。最简单地说，星星的形成是局部引力坍缩的结果，而由此产生的星盘系统的性质取决于气体储存的数量和分布，沿着其运动学和角动量。然而，对分子云的观测揭示了一个动态环境，其中有大尺度的超音速流、显著的切变和超音速湍流的证据。云内密度较大的气体与正在形成的星星的位置有关，它们呈现出更有序的结构，从一个包含密集团块和核心的细丝网络开始。这些细丝中的一些可能表示激波前缘界面，而其他细丝可能直接与云内的重力下降有关。事实上，人们预期分子云内部结构的形成是由于重力和大尺度超音速（湍流）运动之间的竞争。磁场调解也可能发挥重要作用。

The bulk of the star formation in our Galaxy takes place within giant molecular clouds. At its simplest, the formation of a star is the result of localized gravitational collapse and the properties of the resulting star-disk system are dependent on the amount and distribution of the gas reservoir, along with its kinematics and angular momentum. Observations of molecular clouds, however, reveal a dynamic environment with large-scale supersonic flows, significant shear, and evidence for supersonic turbulence. The denser gases within the clouds, which correlate with the locations of on-going star formation, show a more ordered structure, beginning with a network of filaments housing dense clumps and cores. Some of these filaments may denote shock front interfaces and others may relate directly to the gravitational infall within the cloud. Indeed, it is expected that the formation of structure within a molecular cloud is due to the competition between gravity and large-scale supersonic (turbulent) motion. Magnetic field mediation may also play an important role.