The formation of the black hole in the X-ray binary system V404 Cyg

TL;DR

This study measures the motion of the black hole in V404 Cyg, concluding it formed via a supernova with significant mass loss or asymmetries, rather than direct collapse, based on its peculiar velocity.

Contribution

It provides the first precise measurement of V404 Cyg's proper motion and derives its 3D velocity, offering new insights into black hole formation mechanisms in X-ray binaries.

Findings

Black hole's peculiar velocity is approximately 64 km/s.

Formation involved a supernova with mass loss or asymmetries.

Black hole likely formed with about 9 solar masses.

Abstract

Using new and archival radio data, we have measured the proper motion of the black hole X-ray binary V404 Cyg to be 9.2+/-0.3 mas/yr. Combined with the systemic radial velocity from the literature, we derive the full three-dimensional heliocentric space velocity of the system, which we use to calculate a peculiar velocity in the range 47-102 km/s, with a best fitting value of 64 km/s. We consider possible explanations for the observed peculiar velocity, and find that the black hole cannot have formed via direct collapse. A natal supernova is required, in which either significant mass (approximately 11 solar masses) was lost, giving rise to a symmetric Blaauw kick of up to 65 km/s, or, more probably, asymmetries in the supernova led to an additional kick out of the orbital plane of the binary system. In the case of a purely symmetric kick, the black hole must have been formed with a mass of approximately 9 solar masses, since when it has accreted 0.5-1.5 solar masses from its companion.