On the stability and collisions in triple stellar systems

A significant fraction of main sequence stars are part of a triple system. We study the long-term stability and dynamical outcomes of triple stellar systems using a large number of long-term direct N-body integrations with relativistic precession. We find that the previously proposed stability criteria by Eggleton & Kiseleva 1995 and Mardling & Aarseth 2001 predict the stability against ejections reasonably well for a wide range of parameters. Assuming that the triple stellar systems follow orbital and mass distributions from FGK binary stars in the field, we find that in ~1% and ~0.5% of the triple systems lead to a direct head-on collision (impact velocity ~ escape velocity) between main sequence (MS) stars and between a MS star and a stellar-mass compact object, respectively. We conclude that triple interactions are the dominant channel for direct collisions involving a MS star in the field with a rate of one event every ~100 years in the Milky Way. We estimate that the fraction of triple systems that forms short-period binaries is up to ~23% with only up to ~13% being the result of three-body interactions with tidal dissipation, which is consistent with previous work using a secular code.