The First Stars: Formation, Properties, and Impact

Abstract

The first generation of stars, often called Population III (or Pop III), form from metal-free primordial gas at redshifts z ∼ 30 and below. They dominate the cosmic star-formation history until z ∼ 15–20, at which point the formation of metal-enriched Population II stars takes over. We review current theoretical models for the formation, properties, and impact of Pop III stars and discuss existing and future observational constraints. Key takeaways from this review include the following: ▪ Primordial gas is highly susceptible to fragmentation and Pop III stars form as members of small clusters with a logarithmically flat mass function. ▪ Feedback from massive Pop III stars plays a central role in regulating subsequent star formation, but major uncertainties remain regarding its immediate impact. ▪ In extreme conditions, supermassive Pop III stars can form, reaching masses of several 105 M⊙. Their remnants may be the seeds of the supermassive black holes observed in high-redshift quasars. ▪ Direct observations of Pop III stars in the early Universe remain extremely challenging. Indirect constraints from the global 21-cm signal or gravitational waves are more promising. ▪ Stellar archeological surveys allow us to constrain both the low-mass and the high-mass ends of the Pop III mass distribution. Observations suggest that most massive Pop III stars end their lives as core-collapse supernovae rather than as pair-instability supernovae. Expected final online publication date for the Annual Review of Astronomy and Astrophysics, Volume 61 is August 2023. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Zero Metallicity with Zero CPU Hours: Masses of the First Stars on the Laptop

“…Actually, recent hydrodynamic simulations of primordial star formation have converged on the picture that Pop III star-forming disks typically undergo fragmentation and produce multiple protostars (Turk et al 2009;Stacy et al 2010;Clark et al 2011;Greif et al 2011;Susa 2019;Haemmerlé et al 2020;Liu et al 2020;Klessen & Glover 2023) unless stabilized by strong magnetic fields (e.g., Sharda et al 2020Sharda et al , 2021Hirano & Machida 2022). The formation and evolution of protostars during disk fragmentation (e.g., growth by competing accretion, mergers, and ejections by gravitational scatters) are still poorly understood due to the limited resolution and/or time coverage of current simulations.…”

Spectacular Nucleosynthesis from Early Massive Stars

“…Since even JWST is unable to directly observe the first massive stars (e.g., Schauer et al 2020), these chemical abundances are one of the few ways to understand how the first stars formed and died. Theoretically, one of the most robust predictions is that the first metal-free stars should have a top-heavy initial mass function with a characteristic mass of 10 M e (e.g., Bromm 2013; Klessen & Glover 2023). This prediction, however, is still not confirmed observationally, nor is there a clear understanding of when or how the initial mass function transitions to its present-day shape (e.g., Offner et al 2014;Sharda & Krumholz 2022).…”

A Global Semianalytic Model of the First Stars and Galaxies Including Dark Matter Halo Merger Histories

“…Theoretical calculations based on the standard model of cosmology predict that the first stars began illuminating the Universe within the first ∼100 Myr that followed the Big Bang. Simulations indicate these stars, categorized as Population III (PopIII) stars, formed from primordial metal-free gas within dark matter (DM) "minihalos" (M vir = 10 5 -10 6 M e ), with much higher masses (M * = 10-1000 M e ) than metal-enriched stars (for a recent review, see Klessen & Glover 2023). Thus, the first PopIII stars likely had stellar lifetimes of only a few megayears (Schaerer 2002).…”