Merging Binaries in the Galactic Center: The eccentric Kozai-Lidov mechanism with stellar evolution

TL;DR

This study investigates how the eccentric Kozai-Lidov mechanism, combined with stellar evolution, causes binary stars near the Galactic Center to merge, potentially explaining some observed objects and populations.

Contribution

It introduces a comprehensive Monte Carlo simulation approach to model binary mergers in the Galactic Center considering multiple physical effects.

Findings

13% of binaries merge within a few million years

29% of binaries merge within a few billion years

Merged systems may relate to G2-like objects and young stellar populations

Abstract

Most, if not all, stars in the field are born in binary configurations or higher multiplicity systems. In dense stellar environment such as the Galactic Center (GC), many stars are expected to be in binary configurations as well. These binaries form hierarchical triple body systems, with the massive black hole (MBH) as the third, distant object. The stellar binaries are expected to undergo large amplitude eccentricity and inclination oscillations via the so-called "eccentric Kozai-Lidov" (EKL) mechanism. These eccentricity excitations, combined with post main sequence stellar evolution, can drive the inner stellar binaries to merge. We study the mergers of stellar binaries in the inner 0.1 pc of the GC caused by gravitational perturbations due to the MBH. We run a large set of Monte Carlo simulations that include the secular evolution of the orbits, general relativistic precession, tides, and post-main-sequence stellar evolution. We find that about 13 % of the initial binary population will have merged after a few million years and about 29 % after a few billion years. These expected merged systems represent a new class of objects at the GC and we speculate that they are connected to G2-like objects and the young stellar population.