A grand challenge for modern astrophysics is to understand star and galaxy formation in the first billion years of cosmic history. In particular, the first generation of stars born in extremely metal-poor/free primordial gas, the so-called population III (Pop III), are believed to have distinct features compared with present-day stars: They are more likely to become massive black holes due their massive and compact nature. Recent hydrodynamic simulations of first star formation converge on a 'standard’ picture that Pop III stars form in small clusters by disk instability where binaries and multiples are common, implying that they are promising progenitors of compact object mergers whose gravitational wave signals can be a powerful probe of early star formation. In this talk, I will share my views on the theoretical efforts and challenges in modeling the Pop III binaries and the resulting compact object mergers. I will introduce a physically motivated model for Pop III star clusters from which we conduct N-body simulations to predict the binary statistics, showing that close binaries are likely rare for Pop III stars. I will discuss the implications of our results on the evolution pathways of Pop III compact object mergers, including the classical isolated binary stellar evolution channel and a dynamical channel via nuclear star clusters. Combining the two channels, we find that although Pop III stars only make up a tiny (~10^-5) fraction of all stars ever formed in the Universe, a much higher fraction of massive black hole mergers, up to a few percent, can originate from Pop III stars. If time allows, I can also talk about our recent progress in two related topics, high-redshift X-ray binaries and the effects of primordial black holes on early star formation.
Host: Yi Mao
