$N$-body modelling of the ED-2 stream progenitor shows Gaia BH3's formation involved dynamical interactions

TL;DR

This study uses N-body simulations to demonstrate that Gaia BH3 likely formed through complex dynamical interactions in its progenitor cluster, challenging isolated binary evolution scenarios.

Contribution

It provides the first detailed dynamical modeling of Gaia BH3's formation, emphasizing the role of cluster interactions over isolated evolution.

Findings

Gaia BH3 most likely formed as an exchange binary with multiple dynamical interactions.

Cluster dynamics are crucial in assembling Gaia BH3, not isolated evolution.

Disfavors low-density cluster or isolated formation scenarios for Gaia BH3.

Abstract

Context. The Gaia collaboration announced the discovery of a binary of a massive black hole (33 M$_\odot$) with a low-mass giant star (Gaia BH3) in the ED-2 stellar stream. The properties of this binary, as well as its position in the stream, challenge a formation scenario invoking only isolated binary evolution. Aims. We aim to quantify the importance of dynamics in the formation of Gaia BH3 in the progenitor cluster of the ED-2 stream. Methods. We perform detailed N-body simulations of the progenitor cluster of the ED-2 stream, including the effects of single and binary stellar evolution. We compare these simulations to observations of the ED-2 stream and the properties of Gaia BH3. Results. We determine that Gaia BH3 most likely formed as an exchange binary which underwent multiple strong dynamical interactions. We highlight the importance of cluster dynamics in assembling Gaia BH3, and disfavour a formation scenario where it evolved in isolation and/or in a low-density cluster. Conclusions. The role of dynamics should be considered when interpreting properties of star-black hole binaries found in the next Gaia Data Release.