Properties of OB star−black hole systems derived from detailed binary evolution models

Abstract

Context. The recent gravitational wave measurements have demonstrated the existence of stellar mass black hole binaries. It is essential for our understanding of massive star evolution to identify the contribution of binary evolution to the formation of double black holes. Aims. A promising way to progress is investigating the progenitors of double black hole systems and comparing predictions with local massive star samples such as the population in 30 Doradus in the Large Magellanic Cloud (LMC). Methods. To this purpose, we analyse a large grid of detailed binary evolution models at LMC metallicity with initial primary masses between 10 and 40 M , and identify which model systems potentially evolve into a binary consisting of a black hole and a massive main sequence star. We then derive the observable properties of such systems, as well as peculiarities of the OB star component. Results. We find that ∼3% of the LMC late O and early B stars in binaries are expected to possess a black hole companion, when assuming stars with a final helium core mass above 6.6 M to form black holes. While the vast majority of them may be X-ray quiet, our models suggest that these may be identified in spectroscopic binaries, either by large amplitude radial velocity variations ( ∼ > 50 km s −1 ) and simultaneous nitrogen surface enrichment, or through a moderate radial velocity ( ∼ > 10 km s −1 ) and simultaneously rapid rotation of the OB star. The predicted mass ratios are such that main sequence companions could be excluded in most cases. A comparison to the observed OB+WR binaries in the LMC, Be/X-ray binaries, and known massive BH binaries supports our conclusion. Conclusions. We expect spectroscopic observations to be able to test key assumptions in our models, with important implications for massive star evolution in general, and for the formation of double-black hole mergers in particular.

A naked-eye triple system with a nonaccreting black hole in the inner binary

“…However, the two luminous components of HR 6819 have masses of only ∼6 M and are very far apart, therefore the current BH will remain the only BH in HR 6819, and neither will an NS form. It appears noteworthy that the pure binary models of Langer et al (2020b) predict a steep decrease in the fraction of BH companions toward the masses of the inner B stars in HR 6819 and LB-1. It may be useful to extend the models to triple systems.…”

The impact of mass-transfer physics on the observable properties of field binary black hole populations

“…The accretor then quickly reaches critical rotation and halts further accretion, leading to a highly inefficient mass transfer (a few to a few tens percent; e.g. de Mink et al 2013;Langer et al 2020). On the other hand, if one assumes that the AM is dissipated efficiently before it reached the accretor's surface, and that that the material that is added onto the star has similar specific AM to that of its own surface layers, then MT can be significantly more efficient.…”

The role of mass transfer and common envelope evolution in the formation of merging binary black holes

“…The majority of predicted binary BHs that formed through CE evolution or stable MT in an isolated binary involve an initial phase of stable MT. This removes the hydrogen envelope of the more massive star and leads to the formation of a wide single degenerate binary (Dominik et al 2012;Langer et al 2020). When the secondary evolves and thus fills its Roche lobe, depending on its response to mass loss and the mass ratio of the system, it can undergo a CE phase which ejects the envelope of the secondary at the cost of hardening the binary (cf.…”