In binary star systems, mass transfer can spin up the accretor, possibly leading to efficient chemical mixing and chemically quasi-homogeneous evolution (CHE). Here, we explore the effects of accretion-induced CHE on both stellar populations and their compact binary remnants with the state-of-the-art population synthesis code SEVN. We find that CHE efficiently enhances the formation of Wolf-Rayet stars (WRs) from secondary stars, which are spun-up by accretion, while simultaneously preventing their evolution into red supergiant stars (RSGs). Including CHE in our models increases the fraction of WRs in our stellar sample by nearly a factor of $\approx3$ at low metallicity ($Z=0.001$). WRs formed through CHE are, on average, more massive and luminous than those formed without CHE. Most WRs formed via CHE end their life as black holes. As a direct consequence, the CHE mechanism enhances the formation of binary black holes (BBHs) and black hole-neutron star (BHNS) systems, while simultaneously quenching the production of binary neutron stars (BNSs). However, CHE significantly quenches the merger rate of BBHs, BHNSs and BNSs at low metallicity ($Z\leq{}0.004$), because most binary compact objects formed via CHE have large orbital periods. For instance, the number of BBH and BHNS mergers decreases by one order of magnitude at $Z=0.004$ in the CHE model compared to the standard scenario. Finally, we find that secondary stars experiencing CHE frequently produce the most massive compact object in the binary system. In BHNSs, this implies that the black hole progenitor is the secondary star. Conversely, BBHs formed through accretion-induced CHE likely have asymmetric black hole components, but only a negligible fraction of these asymmetric systems ultimately merge within an Hubble time.
The chemically homogeneous evolutionary channel for binary black hole mergers: rates and properties of gravitational-wave events detectable by advanced LIGO
A grid of fast-rotating, chemically-homogeneous, supernova and/or long-GRB progenitors
University of Arizona（亚利桑那大学）；Flatiron Institute（平顿研究所）；Massachusetts Institute of Technology（麻省理工学院）；University of Colorado（科罗拉多大学）；National Institute of Standards and Technology（美国国家标准与技术研究院）；Michigan State University（密歇根州立大学）
Investigating the Chemically Homogeneous Evolution Channel and its Role in the Formation of the Enigmatic Binary Black Hole Progenitor Candidate HD 5980
本研究通过 MESA 模拟和贝叶斯方法验证大质量双星 HD 5980 A&B 起源于化学均一演化通道，发现其初始质量极高且伴随增强的质量损失，并预测该系统最终将产生双黑洞，或在层级多重系统伴星作用下成为引力波源。
The effect of triples on the Chemically Homogeneous Evolution Channel for producing Gravitational Wave Sources
Max Planck Institute for Astrophysics（马克斯·普朗克天体物理学研究所）；Niels Bohr International Academy, Niels Bohr Institute（尼尔斯·玻尔国际学院，尼尔斯·玻尔研究所）；Radboud University Nijmegen（拉德堡德大学奈梅亨）
