Binary stars and their impact across the Universe

Robert Izzard (Surrey)

In my life over the past decade, it has become increasingly clear that binary systems influence not only the evolution of their component stars but also the bigger structures they inhabit — from star clusters to galaxies and across the Universe at large. In this talk, I will come together with an introduction to binary stars and explain why they matter, before discussing how we model them and their parent populations. I will focus in particular on our binary_c population nucleosynthesis models developed at Surrey. Such binary population synthesis tools are a hard day's computation — a mix of stellar physics and a touch of technical wizardry. I’ll showcase some of the new developments we’ve made to help users get by with a little help from our code, whether they’re running simulations or interpreting the results. Examples include applications to the local stellar population and comparisons with Gaia data, as we follow the sun through our cosmic neighbourhood. I’ll also delve into binary-star nucleosynthesis and the challenges of measuring and modelling the multi-dimensional birth distributions of binaries — essential ingredients for understanding Galactic chemical evolution across galaxies both young and those that were here, there and everywhere. All in all, the outlook for binary-star modelling, and their impact across the Universe, is getting better all the time – not just for today! – though the long and winding road of understanding them still lies ahead.