Astronomy and Astrophysics – Astrophysics
Scientific paper
Jun 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008phdt........21h&link_type=abstract
Proquest Dissertations And Theses 2008. Section 0188, Part 0606 131 pages; [Ph.D. dissertation].United States -- New York: Univ
Astronomy and Astrophysics
Astrophysics
Hydrodynamics, Accretion Disks, Stellar Winds, Planet Formation, Proto-Planetary Disks
Scientific paper
We present a collection of results in theoretical astrophysical hydrodynamics. In order (1), we discuss the role of turbulence in the early stages of planet formation, showing how turbulence in the gas component of proto-planetary disks can hydrodynamically and gravitationally stir the dust from which rocky planets form. We show that turbulence can prevent gravitational collapse of the dust into planetesimals, primarily through gravitational stirring. However, we constrain the strength of the turbulence below which dust collisions are non- destructive and find that, even in the absence of gravitational collapse, planetesimal collisional growth times are not prohibitive. (2) We present results on the truncation of active galactic nuclei (AGN) jets (extremely energetic, highly collimated outflows launched by accretion disks surrounding super-massive black holes). We show that the integrated inertia from stellar winds of the stars contained within the jet can slow and even stop lower luminosity AGN jets, which provides jet composition diagnostics. (3) We examine the shape of stellar wind/interstellar material bow shocks for slow moving stars. We show that in some star/wind systems, the bow shock cannot be in a steady state: the piled up material cannot flow away before gravity overwhelms the wind ram pressure and the material falls back onto the star. (4) We analyze the role of turbulent viscosity as a driver of accretion flows. We show that turbulent viscosity is an incomplete model for turbulence in accretion disks and develop a new mean field framework. This framework shows that the turbulence in a steady state accretion flow maintained only by turbulent viscosity requires an unrealistic efficiency of energy conversion. Further we also find unexpected global instabilities that could lead to disk fragmentation and direct massive planet formation. (5) In the case that Earth-like planets have formed, we present results on the gravitational interaction between the gas disk and imbedded planets. We show that the planet's feedback on the disk cannot be treated as a perturbation even for low planet/star mass ratios. Although the effects are expected to take a long time to appear, this result calls into question the canonical planet migration picture.
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