Spectacular nucleosynthesis from early massive stars (2401.02484v1)

Abstract: Stars formed with initial mass over 50 Msun are very rare today, but they are thought to be more common in the early universe. The fates of those early, metal-poor, massive stars are highly uncertain. Most are expected to directly collapse to black holes, while some may explode as a result of rotationally powered engines or the pair-creation instability. We present the chemical abundances of J0931+0038, a nearby low-mass star identified in early followup of SDSS-V Milky Way Mapper, which preserves the signature of unusual nucleosynthesis from a massive star in the early universe. J0931+0038 has relatively high metallicity ([Fe/H] = -1.76 +/- 0.13) but an extreme odd-even abundance pattern, with some of the lowest known abundance ratios of [N/Fe], [Na/Fe], [K/Fe], [Sc/Fe], and [Ba/Fe]. The implication is that a majority of its metals originated in a single extremely metal-poor nucleosynthetic source. An extensive search through nucleosynthesis predictions finds a clear preference for progenitors with initial mass > 50 Msun, making J0931+0038 one of the first observational constraints on nucleosynthesis in this mass range. However the full abundance pattern is not matched by any models in the literature. J0931+0038 thus presents a challenge for the next generation of nucleosynthesis models and motivates study of high-mass progenitor stars impacted by convection, rotation, jets, and/or binary companions. Though rare, more examples of unusual early nucleosynthesis in metal-poor stars should be found in upcoming large spectroscopic surveys.

• The paper identifies unique nucleosynthesis signatures in metal-poor star J0931+0038, indicating a progenitor mass exceeding 50 solar masses.
• It challenges current theoretical models by presenting an unusual odd-even abundance pattern not reproduced by standard core-collapse scenarios.
• The findings prompt further spectroscopic surveys to uncover similar stars, which could refine understandings of early massive star evolution.

Insights into Early Universe Nucleosynthesis from Massive Stars

The investigation conducted by Alexander P. Ji et al. focuses on the nucleosynthetic signatures preserved in the chemical composition of a nearby metal-poor star, J0931+0038. This research identifies unprecedented nucleosynthesis patterns associated with a massive progenitor star from the early universe, shedding light on the stellar processes that have shaped the chemical evolution of galaxies.

Summary of Findings

J0931+0038, observed through the SDSS-V Milky Way Mapper, presents an intriguing chemical abundance profile. While exhibiting relatively high metallicity ([Fe/H] = -1.76 ± 0.13), it portrays a stark odd-even abundance pattern with dramatically low abundance ratios such as [N/Fe], [Na/Fe], [K/Fe], [Sc/Fe], and [Ba/Fe]. Such ratios suggest that its metals predominantly arose from a single, extremely metal-poor solar mass nucleosynthetic source, hinting at the initial mass of its progenitor being greater than 50 M_⊙.

Interpretations and Implications

The properties of J0931+0038 cannot be matched with current theoretical models, as its extreme abundance features demand reconsideration of progenitor masses and explosion mechanisms. The high metallicity combined with the peculiar abundance pattern points towards the remnants of a massive star ($M > 50 M_\odot$) that may have exploded under unconventional conditions such as those involving significant rotational elements or perhaps using a mechanism linked to pair-creation instability.

1. Astrophysical Context: The chemical paper of metal-poor stars including J0931+0038 provides a vital 'archaeological' insight into the early universe's massive stars. These observations can inform the theorized top-heavy initial mass function (IMF) prevalent when these early stars formed. However, direct observations of such massive progenitor stars are challenging — even for observatories like JWST — making the interpretations of stars like J0931+0038 crucial benchmarks.
2. Nucleosynthesis Challenges: J0931+0038 challenges existing nucleosynthesis models and encourages advancements in understanding stellar phenomena affected by convection, rotation, and potential binary interactions. Traditional core-collapse supernovae models, which typically involve star masses below 50 M_⊙, fail to replicate the observed abundance pattern.
3. Future Directions: The rarity yet significance of stars such as J0931+0038 in understanding early star populations prompts the need for extensive searches via large spectroscopic surveys. Upcoming datasets might uncover similar stars that could become the basis of a refined theoretical framework encompassing early massive star nucleosynthesis.

Concluding Remarks

In conclusion, J0931+0038 invites a critical reassessment of high-mass stellar progenitors and the nucleosynthetic pathways in the early universe. The paper underscores the intersection of observational prowess and theoretical astrophyics. It acts as a call to develop models that integrate complex phenomena such as stellar rotation-induced mixing and binary coalescence, combining these with the astronomical insights that such stars provide. Future research could focus on iterative models that test the bounds of known astrophysical phenomena, thereby expanding our understanding of galactic chemical evolution.