The black hole low mass X-ray binary V404 Cygni is part of a wide hierarchical triple, and formed without a kick

TL;DR

This study discovers that the black hole low-mass X-ray binary V404 Cygni is part of a wide hierarchical triple system, indicating the black hole formed with minimal natal kick and supporting models of black hole formation without significant momentum transfer.

Contribution

The paper provides the first evidence that some black holes can form with nearly no natal kick, based on the hierarchical triple configuration of V404 Cygni.

Findings

V404 Cygni is part of a wide hierarchical triple system.

The black hole likely received a sub-5 km/s natal kick.

The system formed 3-5 billion years ago, with the black hole removing at least half a solar mass.

Abstract

Evidence suggests that when compact objects such as black holes and neutron stars form, they may receive a ``natal kick,'' where the stellar remnant gains momentum. Observational evidence for neutron star kicks is substantial, yet limited for black hole natal kicks, and some proposed black hole formation scenarios result in very small kicks. Here, we report the discovery that the canonical black hole low-mass X-ray binary V404 Cygni is part of a wide hierarchical triple with a tertiary companion at least 3500 astronomical units away from the inner binary. Given the orbital configuration, the black hole likely received a sub-5 kilometer per second kick to have avoided unbinding the tertiary. This discovery reveals that at least some black holes form with nearly no natal kick. Furthermore, the tertiary in this system lends credence to evolutionary models of low-mass X-ray binaries involving a hierarchical triple structure. Remarkably, the tertiary is evolved, indicating that the system formed 3-5 billion years ago, and that the black hole has removed at least half a solar mass of matter from its evolved secondary companion. During the event in which the black hole formed, it is likely that at least half of the mass of the black hole progenitor collapsed into the black hole; it may even have undergone a complete implosion, enabling the tertiary to remain loosely bound.