The first accurate parallax distance to a black hole

TL;DR

This paper reports the most accurate parallax measurement of a Galactic stellar-mass black hole using VLBI, refining its distance, confirming its non-super-Eddington outburst, and providing insights into its formation and jet size.

Contribution

It provides the first precise, model-independent distance to a black hole binary, improving understanding of black hole properties and formation mechanisms.

Findings

Distance to V404 Cyg is 2.39 +/- 0.14 kpc.

Black hole likely formed in a supernova with a recoil kick.

Jet size in quiescence is less than 1.4 AU at 22 GHz.

Abstract

Using astrometric VLBI observations, we have determined the parallax of the black hole X-ray binary V404 Cyg to be 0.418 +/- 0.024 milliarcseconds, corresponding to a distance of 2.39 +/- 0.14 kpc, significantly lower than the previously accepted value. This model-independent estimate is the most accurate distance to a Galactic stellar-mass black hole measured to date. With this new distance, we confirm that the source was not super-Eddington during its 1989 outburst. The fitted distance and proper motion imply that the black hole in this system likely formed in a supernova, with the peculiar velocity being consistent with a recoil (Blaauw) kick. The size of the quiescent jets inferred to exist in this system is less than 1.4 AU at 22 GHz. Astrometric observations of a larger sample of such systems would provide useful insights into the formation and properties of accreting stellar-mass black holes.