  In my thesis I present a study of the dynamics and observational
characteristics of massive circumstellar disks in two dimensions ($r$, $\phi$)
using two complimentary hydrodynamic codes: a `Smoothed Particle Hydrodynamic'
(SPH) code and a `Piecewise Parabolic Method' (PPM) code. I also study the
detection limits available to radial velocity searches for low mass companions
to main sequence stars. The thesis is organized as a series of published or
submitted papers, connected by introductory and concluding material and is
archived `for posterity'. I recommend that readers of this abstract obtain the
published versions of each of these papers. I first outline the progress which
has been made in the modeling of the structure and origins of the solar system,
then in chapter 2 (ApJ 502,p342) I proceed with numerical simulations of
circumstellar disks using both hydrodynamic codes assuming a `locally
isothermal' equation of state. In chapter 4 (ApJ submitted) I relax the locally
isothermal evolution assumption and instead include simple heating and cooling
prescriptions for the system. In chapter 6 (ApJ 500,p940) I examine the limits
which may be placed upon the detection of planets, brown dwarfs and low mass
stellar companions using radial velocity measurements. In chapter 7, I outline
several problems which may be profitably addressed by building on this work.
