Stellar triples with chemically homogeneously evolving inner binaries
Speaker: Andris Dorozsmai
Abstract:
Observations suggest that massive stellar triples are common. However, their evolution is not yet fully understood. In this talk, I discuss the evolution of hierarchical triples in which the stars of the inner binary experience chemically homogeneous evolution (CHE), particularly with the aim to explore the role of the tertiary star in the formation of gravitational-wave (GW) sources. To investigate these systems, I use the the triple-star population synthesis code TRES. I found that about 40 per cent of the all triples harboring a CHE inner binary (CHE triples) experience tertiary mass transfer episodes, an event which is rare for classically evolving stars (i.e. non-CHE stars). In the majority of tertiary mass transfer episodes, the accreting inner binary consists of two main sequence stars (58-60 per cent) or two black holes (24-40 per cent). I will also show that von Zeipel-Lidov-Kozai (ZLK) oscillations play an important role in the evolution of these systems. In particular, I find that for triples with initial outers pericentre smaller than 2000 solar radii, ZLK oscillations can result in eccentric (stellar or double compact object) mergers. Approximately 24 per cent of CHE triples become GW sources. Moreover, in a significant fraction of these sources, the tertiary star plays an important role and leads to configurations that are not predicted for isolated binaries. To conclude, the evolution of CHE binaries can be affected by a close tertiary companion, resulting in astronomical transients such as tertiary-driven massive stellar mergers and equal-mass BH-BH binaries that merge via gravitational-wave emission within Myrs.