Resonant Trapping of Stars by Merging Massive Black Hole Binaries

TL;DR

This study investigates how stars can be resonantly trapped by merging massive black hole binaries, potentially leading to observable electromagnetic signals during the binary coalescence.

Contribution

It provides a numerical analysis of resonant trapping mechanisms in black hole binaries with mass ratio 1/100, highlighting the strength of 2:1 and 4:2 mean motion resonances.

Findings

Resonant trapping can draw objects close to relativistic regimes (~10 Schwarzschild radii).

Inclinations of trapped objects can increase significantly, including retrograde orbits.

Strong 2:1 and 4:2 resonances are identified as key mechanisms.

Abstract

A massive black hole binary might resonantly trap a star (e.g. a white dwarf) and the gas released by its tidal disruption might emit electromagnetic wave signals around the coalescence of the binary. With post-Newtonian equations of motion including gravitational radiation reaction, we numerically studied resonant trappings by black hole binaries with mass ratio 1/100. It is found that 2:1 (and simultaneously 4:2) mean motion resonances of the binaries would be strong and could, in principle, draw small third objects deep into relativistic regimes (e.g. ~10 Schwarzschild radii). The inclinations of the trapped objects could increase significantly and, in some cases, retrograde orbits could be realized eventually.