Triples as Links between Binary Black Hole Mergers, their Electromagnetic Counterparts, and Galactic Black Holes

TL;DR

This paper proposes a new formation pathway linking gravitational-wave black hole mergers, Gaia-observed wide black hole systems, and X-ray binaries, predicting observable electromagnetic counterparts and explaining the origins of some galactic black holes.

Contribution

It introduces a novel three-body dynamical model that connects GW mergers with electromagnetic signals, Gaia BHs, and X-ray binaries, providing a unified formation scenario.

Findings

Approximately 0.02% of LVK mergers may have detectable EM counterparts.

The scenario can account for 1-10% of Gaia BH systems in the Milky Way.

Predicted EM flares are brightest in optical-UV, lasting days to weeks.

Abstract

We propose a formation pathway linking black holes (BHs) observed in gravitational-wave (GW) mergers, wide BH-stellar systems uncovered by Gaia, and accreting low-mass X-ray binaries (LMXBs). In this scenario, a stellar-mass BH binary undergoes isolated binary evolution and merges while hosting a distant, dynamically unimportant tertiary stellar companion. The tertiary becomes relevant only after the merger, when the remnant BH receives a GW recoil kick. Depending on the kick velocity and system configuration, the outcome can be: (i) a bright electromagnetic (EM) counterpart to the GW merger; (ii) an LMXB; (iii) a wide BH-stellar companion resembling the Gaia BH population; or (iv) an unbound, isolated BH. Modeling the three-body dynamics, we find that $\sim 0.02\%$ of LIGO-Virgo-KAGRA (LVK) mergers may be followed by an EM counterpart within $\sim$10 days, produced by tidal disruption of the star by the BH. The flare is likely brightest in the optical-UV and lasts days to weeks; in some cases, partial disruption causes recurring flares with a period of $\sim$2 months. We further estimate that this channel can produce $\sim 1-10\%$ of Gaia BH systems in the Milky Way. This scenario provides the first physically motivated link between GW sources, Gaia BHs, and some X-ray binaries, and predicts a rare but robust pathway for EM counterparts to binary BH mergers, potentially detectable in LVK's O5 run.