Following Accretion Processes in Simulations of Star-Formation using Sink Particles

Abstract

<p>Resolving the wide range of spatial scales simultaneously present in the formation of stars and star clusters is a challenge for numerical simulations. Methods such as adaptive hydrodynamics codes must be used in many gasdynamical simulations where gravity is also present, and constructs known as "sinks" are commonly used to avoid the computational expense of directly simulating the dense regions within protostars. Despite being essential to investigations of star formation over long timescales, numerics can often play an undesired role in the behaviour of these point-mass accretors, causing artificial accretion. In this thesis, the use of sink particles as models of protostars is investigated using the Gasoline <em>N</em>-body + smoothed particle hydrodynamics code. Motivated by observations of disks and accretion rates onto protostars, physical viscosity using the a-parametrization was implemented. Tests of both spherical and rotating protostellar accretion were performed. In spite of their importance to star formation) previously presented rotating tests are subject to several numerical problems; efforts were made in this work to simulate a three-dimensional viscous accretion disk where such issues were identified and minimized. Simulations were performed for varying strengths of viscosity and sink radius, as well as with inner boundary conditions known as "sinking" particles. Angular momentum transport was present and behaved physically in all cases with α > 0, and the average radial velocities and mass-accretion rates in the disks matched finite-difference estimates of corresponding analytic expressions.</p>