On the origin of black hole spin in high-mass black hole binaries: Cygnus X-1

TL;DR

This paper investigates the origin of black hole spin in high-mass binaries, specifically Cygnus X-1, and concludes that the spin likely results from collapse processes rather than binary synchronization.

Contribution

It provides evidence against the binary synchronization hypothesis for black hole spin origin, emphasizing collapse-related processes in Cygnus X-1.

Findings

Binary synchronization unlikely as spin origin

Collapse processes likely determine black hole spin

Cygnus X-1's spin not caused by companion's angular momentum

Abstract

To date, there have been several detections of high-mass black hole binaries in both the Milky Way and other galaxies. For some of these, the spin parameter of the black hole has been estimated. As many of these systems are quite tight, a suggested origin of the spin is angular momentum imparted by the synchronous rotation of the black hole progenitor with its binary companion. Using Cygnus X-1, the best studied high-mass black hole binary, we investigate this possibility. We find that such an origin of the spin is not likely, and our results point rather to the spin being the result of processes during the collapse.