Black Hole-Wolf-Rayet X-ray Binaries with Orbital Periods under 1.5 Days Diagnosed As Potential Gravitational Wave Sources

Black hole and Wolf-Rayet X-ray binaries represent a fascinating class of systems poised to become detectable sources of gravitational waves for observatories like LIGO-Virgo-KAGRA. Zi-Yuan Wang, Ying Qin, and Georges Meynet, alongside colleagues Qing-Zhong Liu, Xin-Wen Shu, and Ya-Wen Xue, present detailed binary evolution models that diagnose the properties and predict the ultimate fates of these intriguing systems. The team incorporates a refined understanding of accretion efficiency and dynamical tides, allowing them to model the evolution of these binaries with unprecedented accuracy. Their work reveals significantly lower upper limits for the black hole masses in IC 10X-1 and NGC 300X-1 than previously thought, suggesting both systems will likely produce merging binary black holes within the next few billion years, while also constraining the spin of the black hole in Cyg X-3 and indicating it may form a lower-mass gap black hole. This research provides crucial insights into the population of merging black holes and enhances the potential for future gravitational wave detections.

These systems are particularly important because their short orbital periods suggest they will eventually merge, creating gravitational waves detectable by instruments like LIGO. Scientists are investigating the dynamics and evolution of these rare binaries to predict the characteristics of the gravitational waves they produce, requiring detailed modelling of the accretion process and the complex interactions between the stars.

High-Mass Binaries and Compact Object Origins

Research focuses on high-mass X-ray binaries, systems where a compact object, either a black hole or neutron star, pulls matter from a massive star. Understanding how these compact objects form and evolve is central to this work, alongside investigations into the life cycle of massive stars, including how they lose mass through stellar winds. A key area of study involves the processes by which matter transfers from the massive star to the compact object, considering both direct overflow and capture from stellar winds. The interplay between the two stars in a binary system is also critical, influencing their evolution through tidal interactions and mass transfer.

Black Hole Masses and Binary Merger Predictions

Detailed computer models of IC 10X-1, NGC 300X-1, and Cyg X-3 have allowed scientists to refine our understanding of these unique systems. A new method for calculating how efficiently material accretes onto the black hole, combined with improved modelling of tidal forces, has provided a more accurate diagnosis of their evolution and potential as gravitational wave sources. The team determined that the black holes in IC 10X-1 and NGC 300X-1 are likely less massive than previously thought, with upper limits of 20 and 15times the mass of our Sun, respectively. Both systems are predicted to form merging binary black holes within a Hubble time, unless the black hole in NGC 300X-1 reaches a mass of 15 solar masses. For Cyg X-3, the research indicates a limited spin for the black hole, and suggests it will likely form a black hole within the lower mass gap, also leading to a merger within a Hubble time.

Black Hole Binaries Evolve Towards Mergers

Computer simulations have revealed that these black hole binaries are evolving towards mergers within a Hubble time. By refining calculations of accretion efficiency and tidal forces, scientists have been able to assess their potential as sources of gravitational waves and determine that the black holes in IC 10X-1 and NGC 300X-1 are less massive than previously estimated. Furthermore, the study suggests the black hole in Cyg X-3 has a limited spin and will likely form a black hole within the lower mass gap, contributing to a better understanding of these unique binary systems and refining predictions for the detection of gravitational waves from similar sources.