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

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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.**