Bondi-Hoyle-Lyttleton Accretion of Cold and Self-Interacting Dark Matter

Abstract

The accretion of a compact object is explored in a Bondi-Hoyle-Lyttleton (BHL) accretion geometry where the sourrounding media consists of dark matter (DM). Theoretical expectations for both cases where the medium is collisionless and collisional are examined to obtain a sense of the properties of the BHL wake that forms in each case, including the size of the Hoyle-Lyttleton radius and magnitude of the accretion rate. N-body simulations of the BHL accretion geometry are performed for the case of cold dark matter (CDM), which is collisionless, and self-interacting dark matter (SIDM), which for large cross sections should approach the collisional case. The results of the simulations are analyzed and show significant differences between the two DM models. The results paint a picture of a denser accretion column (wake) close to the compact object in the case of SIDM and a higher fraction of bounded particles which results in a larger accretion rate than in the case of CDM. The CDM wake is in contrast more disperse whereas for SIDM the velocity dispersion is lower and the velocity dispersion profile flatter. These differences can be explained by collisions of the SIDM particles on their trajectory to form the wake, which results in a net loss of kinetic energy of the wake particles. The larger the cross section, the stronger these differences are.