Effects of primordial black holes on early star formation
Tsung-Dao Lee Institute
Host: Dong Lai
Location: TDLI, Open Area (4F-SW)
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Abstract:
Primordial black holes (PBHs) have long been considered a promising candidate for or an important component of dark matter (DM). Recent gravitational wave (GW) observations of binary black hole (BH) mergers and discoveries at the high-redshift Universe made by JWST have triggered renewed interest in PBHs in the stellar-mass (∼ 10 − 100 Msun) and supermassive regimes (∼ 10^6 − 10^11 Msun). We use cosmological simulations and semi-analytical models to explore the effects of PBHs on early star formation, focusing on two mechanisms: acceleration of structure formation from isocurvature perturbations and (thermal) feedback from BH accretion. Although stellar-mass PBHs do affect the properties of first star-forming halos, the standard picture of first star formation is not changed (for PBH abundances allowed by existing observational constraints), and their global impact on cosmic star formation history is likely minor, as the thermal feedback from PBHs increases the halo mass threshold for star formation, compensating for the enhanced halo abundance. On the other hand, supermassive PBHs may play more important roles as seeds of massive structures, which can explain the apparent overabundance of massive galaxies and overmassive BHs in recent JWST observations. In particular, the special source Abell 2744-QSO1, with an extremely high BH-to-stellar mass ratio and no metal detections, is difficult to reproduce with standard galaxy evolution models in LCDM, but can be naturally explained as a PBH-seeded halo in the early phase dominated by BH feedback. We also find that the UV radiation from PBHs can potentially trigger the formation of direct-collapse BHs, leading to supermassive BH binaries.
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.
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