8 in 10 Stars in the Milky Way Bulge experience stellar encounters within 1000 AU in a gigayear

Abstract

ABSTRACT The Galactic bulge is a tumultuous dense region of space, packed with stars separated by far smaller distances than those in the Solar neighbourhood. A quantification of the frequency and proximity of close stellar encounters in this environment dictates the exchange of material, disruption of planetary orbits, and threat of sterilizing energetic events. We present estimated encounter rates for stars in the Milky Way bulge found using a combination of numerical and analytical methods. By integrating the orbits of bulge stars with varying orbital energy and angular momentum to find their positions over time, we were able to estimate how many close stellar encounters the stars should experience as a function of orbit shape. We determined that ∼80 per cent of bulge stars have encounters within 1000 AU and that half of bulge stars will have >35 such encounters, both over a gigayear. Our work has interesting implications for the long-term survivability of planets in the Galactic bulge.