We explore a newly proposed channel to create binary black holes of stellar origin .
This scenario applies to massive , tight binaries where mixing induced by rotation and tides transports the products of hydrogen burning throughout the stellar envelopes .
This slowly enriches the entire star with helium , preventing the build-up of an internal chemical gradient .
The stars remain compact as they evolve nearly chemically homogeneously , eventually forming two black holes , which , we estimate , typically merge 4–11 Gyr after formation .
Like other proposed channels , this evolutionary pathway suffers from significant theoretical uncertainties , but could be constrained in the near future by data from advanced ground-based gravitational-wave detectors .
We perform Monte Carlo simulations of the expected merger rate over cosmic time to explore the implications and uncertainties .
Our default model for this channel yields a local binary black hole merger rate of about 10 Gpc ^ { -3 } yr ^ { -1 } at redshift z = 0 , peaking at twice this rate at z = 0.5 .
This means that this channel is competitive , in terms of expected rates , with the conventional formation scenarios that involve a common-envelope phase during isolated binary evolution or dynamical interaction in a dense cluster .
The events from this channel may be distinguished by the preference for nearly equal-mass components and high masses , with typical total masses between 50 and 110 { M } _ { \odot } .
Unlike the conventional isolated binary evolution scenario that involves shrinkage of the orbit during a common-envelope phase , short time delays are unlikely for this channel , implying that we do not expect mergers at high redshift .