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BinCosmos Report Summary

Project ID: 661502
Funded under: H2020-EU.1.3.2.

Periodic Reporting for period 1 - BinCosmos (The impact of Massive Binary Stars through Cosmic Times)

Reporting period: 2015-04-01 to 2017-03-31

Summary of the context and overall objectives of the project

Massive stars, i.e. stars that are up to million times brighter than ordinary stars such as our Sun, play many important roles in astrophysics. They can be considered as (I) Cosmic Engines as they transformed the pristine and dark Universe left after the Big Bang into the modern Universe in which we live today. We use them as (II) Cosmic Probes to study the most distant galaxies and we monitor their eruptions and explosions as (III) Cosmic Transients. As a result, various fields in astrophysics heavily rely on the input of stellar models.

The widely-used models are outdated: they consider all massive stars to be single. In recent years, large observing campaigns with world-class telescopes provided quantitative evidence showing that the large majority of massive stars will interact with a close binary companion (e.g. Sana & de Mink et. al. Science 2012). This project investigates and quantifies how binarity affects several of the crucial roles that massive stars played throughout cosmic time. Although pioneering studies have been conducted, the exploration of these effects is still in its infancy. So far progress has been hampered by (I) the challenging nature of the computations, (II) the many uncertainties in the models and until recently (III) the lack of observational constraints. This project overcomes these challenges by combining the strengths of highly complementary state-of-the art computational tools and by making use of the recently available observational data sets.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

For this project extensive simulations and estimates have been made for the impact of binaries interaction, leading to about two dozen refereed publications. As highlight worth mentioning is the response to the unanticipated discovery of gravitational waves which were announced during the duration of the fellowship. The PI responded swiftly with two papers on a new formation channel for the formation of binary black holes (Mandel & de Mink 2017, De Mink & Mandel 2017), completely in line with the original scope of the project.

In addition, results have been obtained on the core science of the project related to the impact of binary interaction, which are published in papers that are lead by PhD students that were directly supervised by the PI. Most notably are a study on how massive stars die as core collapse supernovae (Zapartas, de Mink et al. 2017) and the implications of binary interaction for the ionizing radiation (Gotberg, de Mink et al. 2017).

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

Computations performed and published explore novel ideas for the progenitor evolution of stellar transients and the radiation field of binary products. Direct Socio-economic impact is not expected as direct result of this project which concerns fundamental research. However, indirect impact has been achieved through public outreach.

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