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

银河系中大部分恒星的形成都发生在巨大的分子云中。简单地说，恒星的形成是局部引力坍缩的结果，由此产生的星盘系统的性质取决于气藏的数量和分布，以及它的运动学和角动量。然而，对分子云的观测揭示了一个具有大规模超音速流动、显著剪切和超音速湍流证据的动态环境。云中密度更大的气体，与正在形成的恒星的位置有关，显示出更有序的结构，开始是一个由细丝组成的网络，里面有密集的团块和核心。这些细丝中的一些可能表示激波前界面，另一些可能直接与云内的重力下降有关。事实上，人们预计分子云内部结构的形成是由于重力和大规模超音速（湍流）运动之间的竞争。磁场中介也可能起重要作用。这项发现基金将用于研究质量、能量和动量在分子云和时间中的流动。***为了确定最终状态——一个有行星系统的年轻恒星——有必要了解质量和角动量是如何从致密的出生云核心漏斗下来的。这种致密的云核必须与更大的分子云，特别是与内部丝状结构网络的关系进行研究。最后，云内的形态和运动学，包括丝状结构，与分子云本身的形成和演化有关。更复杂的是，必须考虑几个反馈回路，最关键的是来自形成恒星本身的喷流和风的能量和动量。***我的研究生团队将通过对受激一氧化碳的观察来研究超音速（湍流）激波的重要性，然后进行预期能量耗散率的理论计算。我们将继续积极研究云中的致密气体结构，包括：恒星形成模式的理论研究；前恒星核心引力稳定性的观测测定；并将观测到的岩心稳定范围和演化状态与模拟结果进行了比较。此外，我们将支持通过ALMA观测，通过偶发性爆发来直接研究原恒星质量聚集的可能性。***这项发现基金将使我的团队能够继续在恒星形成领域发挥领导作用，利用最近对分子云的大型调查（JCMT, Herschel, Spitzer），新仪器（ALMA， JWST）前所未有的灵敏度和角度分辨率，以及当前和预期数值模拟中可用的细节水平

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. This Discovery Grant will enable research on the flow of mass, energy, and momentum through molecular clouds and over time.***In order to determine the end-state - a young star with a planetary system - it is necessary to understand how mass and angular momentum funnel down from the dense natal cloud core. This dense cloud core must be investigated in relationship to the larger molecular cloud, and especially to the network of internal filamentary structure. Finally, the morphology and kinematics within the cloud, including the filamentary structure, relate to the formation and evolution of the molecular cloud itself. To complicate matters, several feedback loops must be taken into account, most critically the energy and momentum of jets and winds from the forming stars themselves. ***My graduate student team will investigate the importance of supersonic (turbulent) shocks through observations of excited carbon monoxide, following theoretical calculations of the expected energy dissipation rate. We will continue to actively investigate dense gas structures within clouds through: theoretical work on the modes of star formation; observational determinations of gravitational stability in pre-stellar cores; and comparison of the observed stability range and evolutionary state of cores against simulations. Additionally, we will champion direct investigations into the possibility of proto-star mass assembly via episodic bursts, through ALMA observations. ***This Discovery Grant will enable my team to continue its leadership role in the field of star formation, taking advantage of the recent large surveys of molecular clouds (JCMT, Herschel, Spitzer), the unprecedented sensitivity and angular resolution of new instrumentation (ALMA, JWST), and the level of detail available in current and anticipated numerical simulations.**