Bridging the scales: towards a universal analytical model for Population III star formation
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Online
Tsung-Dao Lee Institute
Host: Dong Lai
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Abstract:
The first stars, also called Population III (Pop III) stars, formed in extremely metal-poor primordial gas with inefficient cooling, are expected to have distinct features compared with present-day metal-enriched stars (more massive, compact, and less mass loss) and play important roles in the first billion years of cosmic history through their radiation, metal enrichment, and by seeding massive black holes (BHs). Although their detailed properties are largely unknown, direct and indirect probes (e.g., deep surveys by JWST, stellar archaeology, binary BH mergers, the 21-cm signal, and reionization) are providing us with increasingly more clues. Self-consistent theoretical predictions of the formation rates, sites, and masses of Pop III stars are crucial for interpreting observations, but are challenging due to complex physical processes operating over an enormous range of physical scales (from sub-au to cosmic). One solution is to combine analytical models for small-scale star formation processes with cosmological simulations that capture large-scale physics regulating the conditions of Pop III star formation (structure formation, radiation backgrounds, and baryon-dark matter streaming motion). To bridge the scales, we build an analytical model to predict the final masses of Pop III stars/clusters from the properties of star-forming clouds, based on the key results of small-scale star formation simulations and stellar evolution models. Our model for the first time considers the interplay between feedback and fragmentation and covers different modes of Pop III star formation ranging from ordinary small (∼ 10 − 1000 M⊙) clusters in molecular-cooling clouds to massive (≳ 10^4 M⊙) clusters containing supermassive (∼ 10^4 − 3 × 10^5 M⊙) stars under violent collapse of atomic-cooling clouds with large gas accretion rates of ≳ 0.1 M⊙/yr. As an example, the model is applied to the Pop III star-forming clouds in the progenitors of typical haloes hosting high-𝑧 luminous quasars (𝑀_h ∼ 10^12 M⊙ at 𝑧 ∼ 6), which shows that formation of Pop III massive clusters is common (∼ 20 − 70%) in such biased (∼ 4𝜎) regions, and the resulting heavy black hole seeds from supermassive stars can account for a significant fraction of observed luminous (≳ 10^46 erg/s) quasars at 𝑧 ∼ 6. I will also discuss the implications of the small-scale modeling of Pop III star formation on direct observations of Pop III star clusters, their long-term evolution, and relevant gravitational-wave signals of binary BH mergers.
Biography:
Boyuan Liu is a postdoctoral research fellow at the Center for Astronomy, University of Heidelberg, working in the group of Prof. Michela Mapelli. His research centers on the formation and evolution of the first stars, black holes, and galaxies at Cosmic Dawn. He employs a combination of semi-analytical calculations and numerical simulations to investigate how these ancient objects shape early cosmic evolution and produce unique signatures in multi-messenger observations, such as star formation history and metal scaling relations of high-redshift galaxies, the 21-cm signal and reionization, gravitational waves from compact object mergers, abundance patterns of metal-poor stars, and seeding and growth of supermassive black holes. He is also interested in constraining fundamental physics, such as the nature of dark matter and primordial black holes, with observable signals from Cosmic Dawn. Before joining Heidelberg, he was a postdoctoral fellow at the Institute of Astronomy, University of Cambridge, working with Prof. Anastasia Fialkov. He earned his PhD from the University of Texas at Austin with the mentorship of Prof. Volker Bromm. He completed his undergraduate studies in physics at Tsinghua University._01.jpg)
