Hypervelocity binary stars: smoking gun of massive binary black holes

TL;DR

This paper predicts that binary stars can be ejected from the Galactic center at hypervelocity speeds through interactions with a massive binary black hole, providing a potential observational signature of such black holes.

Contribution

It introduces a new mechanism for hypervelocity binary star ejection via binary black hole interactions, which is distinct from previous single black hole scattering models.

Findings

Binary stars can reach velocities up to 1000 km/s while remaining intact.

Such high velocities are unlikely from single black hole interactions.

Detection of hypervelocity binary stars would confirm the existence of a massive binary black hole.

Abstract

The hypervelocity stars recently found in the Galactic halo are expelled from the Galactic center through interactions between binary stars and the central massive black hole or between single stars and a hypothetical massive binary black hole. In this paper, we demonstrate that binary stars can be ejected out of the Galactic center with velocities up to 10^3 km/s, while preserving their integrity, through interactions with a massive binary black hole. Binary stars are unlikely to attain such high velocities via scattering by a single massive black hole or through any other mechanisms. Based on the above theoretical prediction, we propose a search for binary systems among the hypervelocity stars. Discovery of hypervelocity binary stars, even one, is a definitive evidence of the existence of a massive binary black hole in the Galactic center.