Stellar Encounters at the Galactic Centre

Abstract: Using methods of smoothed particle hydrodynamics (SPH) an N -body simulation was set-up to investigate stellar encounters between a 1 solar-mass main sequence (MS) star, modeled after the Sun, and a 0.6 solar-mass white dwarf (WD). This was done primarily to investigate the assumptions made by Mastrobuono-Battisti et al. (2021) in search of the impact of stellar encounters on stellar population in nuclear stellar clusters (NSCs). Four different possible outcomes of the encounter were identified and described in detail. The boundary between a merger taking place between the stars and no merger was located in velocity-periastron space. Properties, such as, change in specific orbital energy and mass of the WD were investigated for a set of select encounters sharing the same velocity of the WD to look for relations between different input parameters of the encounter. It was found that the assumptions about no mass loss and the location of the boundary of the merger and no-merger encounters between WDs and MS stars made by Mastrobuono-Battisti et al. (2021) were false. I show that in encounters, where either a physical collision or a merger between the two stars takes place, a substantial amount of unbound mass is produced, and that encounters with periastron values larger than 1.0 solar-radii can result in a merger, given that the kinetic energy of the WD is sufficiently small. The possible effects of these findings on the evolution of stellar population in NSCs were discussed. Less significant relations between the mass accreted by the WD, WDs final velocity, orbital period of the WD in lengthy merger encounters and periastron value of the encounter were also analysed and summarized.