Do high-spin high-mass X-ray binaries contribute to the population of merging binary black holes?

TL;DR

This study investigates whether high-spin, high-mass X-ray binaries significantly contribute to the population of merging binary black holes, finding their contribution is limited due to formation and evolutionary constraints.

Contribution

The paper combines MESA simulations and population synthesis to quantify the role of Case-A mass transfer in forming merging BBHs from high-spin HMXBs, revealing limited contribution.

Findings

Up to 11% of Case-A HMXBs lead to BBH mergers.

Only 20% of BBH mergers originate from Case-A HMXBs.

Most Case-A HMXBs merge or become too wide to merge within a Hubble time.

Abstract

Gravitational-wave observations of binary black hole (BBH) systems point to black hole spin magnitudes being relatively low. These measurements appear in tension with high spin measurements for high-mass X-ray binaries (HMXBs). We use grids of MESA simulations combined with the rapid population-synthesis code COSMIC to examine the origin of these two binary populations. It has been suggested that Case-A mass transfer while both stars are on the main sequence can form high-spin BHs in HMXBs. Assuming this formation channel, we show that depending on critical mass ratios for the stability of mass transfer, 48-100% of these Case-A HMXBs merge during the common-envelope phase and up to 42% result in binaries too wide to merge within a Hubble time. Both MESA and COSMIC show that high-spin HMXBs formed through Case-A mass transfer can only form merging BBHs within a small parameter space where mass transfer can lead to enough orbital shrinkage to merge within a Hubble time. We find that only up to 11% of these Case-A HMXBs result in BBH mergers, and at most 20% of BBH mergers came from Case-A HMXBs. Therefore, it is not surprising that these two spin distributions are observed to be different.