An X-ray quiet black hole born with a negligible kick in a massive binary within the Large Magellanic Cloud

TL;DR

This paper reports the discovery of a unique X-ray faint black hole binary in the Large Magellanic Cloud, providing insights into black hole formation with negligible natal kicks and implications for gravitational wave predictions.

Contribution

It presents the first unambiguous identification of an X-ray quiet black hole binary outside our Galaxy, with orbital and spectral analysis indicating a black hole formed with little or no kick.

Findings

Black hole in VFTS 243 is X-ray faint and in a near-circular orbit.

Spectral analysis confirms the companion is a black hole, not a neutron star or non-degenerate star.

Black hole formation involved minimal ejected material or kick.

Abstract

Stellar-mass black holes are the final remnants of stars born with more than 15 solar masses. Billions are expected to reside in the Local Group, yet only few are known, mostly detected through X-rays emitted as they accrete material from a companion star. Here, we report on VFTS 243: a massive X-ray faint binary in the Large Magellanic Cloud. With an orbital period of 10.4-d, it comprises an O-type star of 25 solar masses and an unseen companion of at least nine solar masses. Our spectral analysis excludes a non-degenerate companion at a 5-sigma confidence level. The minimum companion mass implies that it is a black hole. No other X-ray quiet black hole is unambiguously known outside our Galaxy. The (near-)circular orbit and kinematics of VFTS 243 imply that the collapse of the progenitor into a black hole was associated with little or no ejected material or black-hole kick. Identifying such unique binaries substantially impacts the predicted rates of gravitational-wave detections and properties of core-collapse supernovae across the Cosmos.