A single low-energy, iron-poor supernova as the source of metals in the star SMSS J 031300.36-670839.3 (1402.1517v1)

Abstract: The element abundance ratios of four low-mass stars with extremely low metallicities indicate that the gas out of which the stars formed was enriched in each case by at most a few, and potentially only one low-energy, supernova. Such supernovae yield large quantities of light elements such as carbon but very little iron. The dominance of low-energy supernovae is surprising, because it has been expected that the first stars were extremely massive, and that they disintegrated in pair-instability explosions that would rapidly enrich galaxies in iron. What has remained unclear is the yield of iron from the first supernovae, because hitherto no star is unambiguously interpreted as encapsulating the yield of a single supernova. Here we report the optical spectrum of SMSS J031300.36- 670839.3, which shows no evidence of iron (with an upper limit of 10^-7.1 times solar abundance). Based on a comparison of its abundance pattern with those of models, we conclude that the star was seeded with material from a single supernova with an original mass of ~60 Mo (and that the supernova left behind a black hole). Taken together with the previously mentioned low-metallicity stars, we conclude that low-energy supernovae were common in the early Universe, and that such supernovae yield light element enrichment with insignificant iron. Reduced stellar feedback both chemically and mechanically from low-energy supernovae would have enabled first-generation stars to form over an extended period. We speculate that such stars may perhaps have had an important role in the epoch of cosmic reionization and the chemical evolution of early galaxies.

• The paper finds that the extremely metal-poor star SMSS J031300.36-670839.3 was likely enriched by a single, low-energy, iron-poor supernova, challenging the prevailing model of massive pair-instability supernovae.
• High-resolution spectroscopy established a stringent upper limit for the star's iron content ([Fe/H] < -7.1) and revealed a decoupled calcium abundance, providing key evidence for enrichment by a single, low-energy event.
• This finding challenges existing models of early universe chemical evolution, suggesting low-energy supernovae played a significant role in the formation of metal-poor stars and the epoch of cosmic reionization.

Analysis of Metal Enrichment in Low-Metallicity Stars: A Case Study of SMSS 031300.36-670839.3

This paper provides a comprehensive analysis of the element abundance ratios in the star SMSS J031300.36-670839.3 (hereafter SMSS 0313-6708), a low-mass star exhibiting extremely low metal content. The paper challenges the prevailing assumption that the enrichment of early-universe materials was dominated by massive stars experiencing pair-instability supernovae, which are expected to produce significant iron. Instead, the observed abundance pattern in SMSS 0313-6708 suggests enrichment by a single low-energy supernova event, pointing to a previously underappreciated mechanism involving low-mass supernovae that yield light elements like carbon, but minimal iron.

Key Findings

The core finding of the paper is the extremely low iron abundance in SMSS 0313-6708, characterized by an upper limit of [Fe/H] < -7.1. Such a severe iron deficiency underscores the star's formation from gas enriched by potentially a single supernova with low explosion energy and a progenitor mass of approximately 60 M☉. This paradigm contrasts with the expected pair-instability events for the first stars, which would canonically result in higher iron yields.

The paper's methodology includes high-resolution spectroscopy, placing stringent upper limits on the star's iron content. Remarkably, SMSS 0313-6708's spectrum demonstrates a scarcity of detectable iron lines, with the observed highest-confidence upper limits further supporting the hypothesis of a single-enrichment event. The apparent abundance of calcium ([Ca/H] = -7.0) decoupled from iron reflects specific nucleosynthetic processes during the star's hydrogen-burning phase, contrasting with solar abundances.

Theoretical and Practical Implications

The conclusions drawn from SMSS 0313-6708 formation challenge existing models of chemical evolution in the early universe. The implications are twofold: (1) low-energy supernovae may have been more prevalent than previously thought, impacting our understanding of metal-poor star formation; and (2) their role in the extended formation period of Population III stars might have contributed significantly to the epoch of cosmic reionization.

Furthermore, the observed abundance pattern argues against supernova progenitors outside the 10-70 M☉ range due to their respective iron content and carbon enhancements or deficits. Notably, pair-instability supernovae, while massive, are ruled out by the lack of predicted elemental signatures in SMSS 0313-6708.

Future Considerations

This paper opens pathways for further exploration into the implications of supernova diversity and their consequent effects on galactic chemical evolution. Future work could focus on refining nucleosynthetic yield models for supernovae with varying energy levels to better match observed abundances in other ultra-metal-poor stars. Additionally, simulations that incorporate the suggested slower mixing of supernova ejecta could provide insight into the continuity of Population III star formation, potentially reconciling current gaps in understanding cosmic reionization.

In summary, the findings regarding SMSS 0313-6708 challenge prevailing theories and underscore the need for a nuanced understanding of early stellar contributions to the cosmic chemical inventory. дальнейшие исследования в этой области могут пролить свет на более широкие аспекты астрономии, включая формирование галактик и эволюцию структуры Вселенной.