UC Berkeley

I investigate the role of gravitation, turbulence, and radiation in forming low-mass stars.

Molecular clouds are observed to be turbulent, but the origin of this turbulence is not

well understood. Using a gravito-hydrodynamics adaptive mesh refinement (AMR) code, I study the properties of cores and protostars in simulations in which the turbulence is driven to maintain virial balance and where it is allowed to decay. I demonstrate that cores forming in a decaying turbulence environment produce high-multiplicity protostellar systems with Toomre-Q unstable disks that exhibit characteristics of competitive accretion. In contrast, cores forming in a virialized cloud produce smaller protostellar systems with fewer low-mass members.

Observations of molecular clouds are limited by projection, resolution, and the coupling between density and velocity information that is inherent in the molecular tracers commonly used to map molecular clouds. To compare with observations of core kinematics and shapes, I post-processs the simulations to obtain dust emission maps and molecular line information. I demonstrate that some simulated observations are significantly different in the driven and decaying turbulence simulations, making them potential diagnostics for characterizing turbulence in observed star-forming clouds.

Although forming stars emit a substantial amount of radiation into their natal environment, the effects of radiative feedback on the star formation process have not been well studied.

I perform simulations of protostars forming in a turbulent molecular cloud including grey flux-limited diffusion radiative transfer.

I compare the distributions of stellar masses, accretion rates, and temperatures in simulations with and without radiative transfer, and I demonstrate that radiative feedback has a profound effect on accretion, multiplicity, and mass by reducing the number of stars formed and the total rate at which gas turns into stars. I also show that protostellar radiation is the dominant source of energy in the simulation, exceeding viscous dissipation and compressional heating by at least an order of magnitude.

Although heating from protostars is mainly confined within the core envelope, I find that it is sufficient to suppress disk fragmentation that would otherwise result in very low-mass companions or brown dwarfs. I compare the simulation results with recent observations of local low-mass star forming regions and discuss the "luminosity problem."

For future radiative transfer studies of star formation, I add multigroup radiative diffusion capability to the ORION AMR code.