Relativistic tidal separation of binary stars by supermassive black holes

Abstract

A binary stellar system that ventures too close to a supermassive black hole can become tidally separated. In this article, we investigate the role of relativistic effects in these encounters through 3-body simulations. We use the Hybrid Relativistic-Newtonian Approximation (HRNA), which combines the exact relativistic acceleration from a Schwarzschild black hole with a Newtonian description of the binary's self-gravity. This method is compared against Newtonian and Post-Newtonian (1PN) simulations. Our findings show good agreement between HRNA and 1PN results, both of which exhibit substantial differences from Newtonian simulations. This discrepancy is particularly pronounced in retrograde encounters, where relativistic simulations predict up to $30\%$ more separation events and an earlier onset of binary separation ($\beta=2$ compared to $2.5$ in Newtonian simulations, with $\beta$ the impact parameter). Additionally, the HRNA model predicts about 15$\%$ more potential extreme mass ratio inspirals and generate a higher number of hypervelocity star candidates, with velocities up to 2,000 km/s faster than those predicted from Newtonian simulations. Furthermore, compared to Newtonian cases, relativistic encounters are more likely to result in direct stellar collisions and binary mergers.