Finding Close Encounters: Toward a Consensus on the Influence of Stellar Flybys on the Solar System over 10 Million Years

This thesis is a study of possible stellar encounters of the Sun, both in the past and in the future within ± 10 Myr of the current epoch. This study is based on data gleaned from the first Gaia data release (Gaia DR1). One of the components of the Gaia DR1 is the TGAS catalogue. TGAS contained five astrometric parameters for more than two million stars. Four separate catalogues were used to provide radial velocities for these stars. A linear motion approximation was used to make a cut within an initial catalogue keeping only the stars that would have perihelia within 10 pc. 1003 stars were found to have a perihelion distance less than 10 pc. Each of these stars was then cloned 1000 times from their covariance matrix from Gaia DR1. The stars’ orbits were numerically integrated through a model galactic potential. After the integration, a particularly interesting set of candidates was selected for deeper study. In particular stars with a mean perihelion distance less than 2 pc were chosen for a deeper study since they will have significant influence on the Oort cloud. 46 stars were found to have a mean perihelion distance less than 2 pc. Among them HIP 89825 (GL 710) still remains the closest encounter with a Solar System with a perihelion of 0.4-0.8 pc, 1.35 Myr in the future. A principal component analysis was performed in order to show the distribution of the clones around the Oort cloud. The thesis also looks into the influence of the solar apex motion on the distribution of encounter perihelia directions. Some new close encounters have been identified and refinements have been made on encounters reported in previous studies