In this dissertation, I explore the time-variable rate of star formation, using both numerical and analytic techniques. I discuss the dynamics of collapsing regions, the effect of protostellar jets, and development of software for use in the hydrodynamic code RAMSES. I perform high-resolution adaptive mesh refinement simulations of star formation in self-gravitating turbulently driven gas. I have run simulations including hydrodynamics (HD), and HD with protostellar jet feedback. Accretion begins when the turbulent fluctuations on largescales, near the driving scale, produce a converging flow. I find that the character of the collapse changes at two radii, the disk radius rd, and the radius r* where the enclosed gas mass exceeds the stellar mass. This is the first numerical work to show that the density evolves to a fixed attractor, ρ(r, t) → ρ( r), for rd < r < r*; mass flows through this structure onto a sporadically gravitationally unstable disk, and from thence onto the star. The total stellar mass M*(t) ~ (t – t*)2, where (t – t *)2 is the time elapsed since the formation of the first star. This is in agreement with previous numerical and analytic work that suggests a linear rate of star formation. I show that protostellar jets change the normalization of the stellar mass accretion rate, but do not strongly affect the dynamics of star formation in hydrodynamics runs. In particular, M*(t) ∞ (1 – f jet)2(t – t*) 2 is the fraction of mass accreted onto the protostar, where fjet is the fraction ejected by the jet. For typical values of fjet ~ 0.1 – 0.3 the accretion rate onto the star can be reduced by a factor of two or three. However, I find that jets have only a small effect (of order 25%) on the accretion rate onto the protostellar disk (the "raw" accretion rate). In other words, jets do not affect the dynamics of the infall, but rather simply eject mass before it reaches the star. Finally, I show that the small scale structure—the radial density, velocity, and mass accretion profiles—are very similar in the jet and no-jet cases.
|Commitee:||Creighton, Jolien, Erb, Dawn, Kaplan, David, Wiseman, Alan|
|School:||The University of Wisconsin - Milwaukee|
|School Location:||United States -- Wisconsin|
|Source:||DAI-B 79/09(E), Dissertation Abstracts International|
|Keywords:||Galaxy formation, Star clusters, Star formation, Star turbulence|
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