Master's Thesis Defense by Philip Jon Østergaard Kirkeberg

Title: Numerical study of gaseous dynamical friction

Abstract: By use of the hydrodynamical code Athena++, we perform numerical experiments to investigate the influence of a gravitating mass moving through a uniform gaseous medium on a rectilinear, circular and elliptical trajectory, and employ concepts from linear perturbation and Bondi-Hoyle-Lyttleton accretion theory to analyse our results. In the limit of $GM_{\rm p}/(c_{\rm s}^2r_{\rm s})<<1$ we find both the density perturbations and gaseous dynamical friction force to agree with the results of linear perturbation theory, granted $r_{\rm min}/r_{\rm s}=2.25$.  For supersonic perturbers with $GM_{\rm p}/(c_{\rm s}^2r_{\rm s})>1$ in rectilinear motion, the linear approximation is found to significantly overestimate the force due to the formation of a nearly front-back symmetric hydrostatic envelope around the perturber. The central envelope is found to cause the formation of a bow-shock which replaces the Mach-cone of linear theory.

Advisors: Daniel D’Orazio, Martin Pessah, Johan Samsing

Censor:  Jérôme Chenevez (DTU)