Researchers discover chemical evidence for pair-instability supernova from a very massive first star

Newswise — The initial stars lit up the Cosmos throughout the Cosmic Dawn and concluded the cosmic "black era" succeeding the Big Bang. Yet, unraveling the arrangement of their mass remains an enigma of cosmic proportions.

Simulations predict that the inaugural stars acquired masses of up to a few hundred solar masses. Within this range, stars weighing between 140 and 260 solar masses ultimately experienced pair-instability supernovae (PISNe). These PISNe diverge significantly from typical supernovae types, such as Type II and Type Ia, and were expected to leave behind a distinct chemical imprint in the atmospheres of subsequent generation stars. Nevertheless, this anticipated signature has yet to be discovered.

A recent research, spearheaded by Prof. ZHAO Gang from the National Astronomical Observatories of the Chinese Academy of Sciences (NAOC), has unveiled a chemically distinct star named LAMOST J1010+2358 in the Galactic halo. This discovery provides compelling evidence for the existence of pair-instability supernovae (PISNe) originating from extremely massive initial stars during the early stages of the Universe. The conclusions drawn from the study are based on data gathered through the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) survey, complemented by subsequent high-resolution spectra observations conducted by the Subaru Telescope. The investigations have successfully verified that this particular star was formed within a gas cloud predominantly influenced by the products of a pair-instability supernova, boasting a mass equivalent to 260 solar masses.

The team also includes the researchers from Yunnan Observatories of CAS, National Astronomical Observatory of Japan and Monash University, Australia.

After conducting further high-resolution spectroscopic observations of J1010+2358 using the Subaru telescope, the research team has successfully determined the abundances of over ten elements. The standout characteristic of this star lies in its remarkably depleted levels of sodium and cobalt. In fact, its sodium-to-iron ratio is less than 1/100th of the solar abundance. Additionally, J1010+2358 displays a significant disparity in abundance between elements with odd and even charge numbers. Notably, there is a substantial difference in abundance between sodium and magnesium, as well as cobalt and nickel. These findings highlight the distinct chemical composition of this star.

Dr. XING Qianfan, the study's primary author, affirms that the unusual discrepancy between odd and even elements, coupled with the observed scarcities of sodium and α-elements in this star, aligns with the expectations of primordial pair-instability supernovae (PISNe) originating from initial stars with a mass of 260 solar masses. This confirmation further reinforces the research team's conclusions regarding the star's chemical composition and its connection to the primordial PISN phenomenon.

The identification of J1010+2358 serves as direct evidence supporting the theory of hydrodynamical instability caused by electron-positron pair production in the evolutionary process of extremely massive stars. The formation of electron-positron pairs within the star's core results in a reduction of thermal pressure, subsequently triggering a partial collapse. This discovery provides valuable insights into the mechanisms driving the evolution of very massive stars and sheds light on the complex interplay between fundamental particles and stellar dynamics.

Prof. ZHAO Gang, the corresponding author of the study, emphasizes the significance of the discovery by stating that it offers a crucial clue for understanding the initial mass function during the early stages of the universe. Prior to this research, no evidence of supernovae originating from such exceptionally massive stars had been identified in metal-poor stars. The newfound evidence not only fills this gap but also provides valuable insights for refining our understanding of stellar evolution and the distribution of initial masses in the early universe. This discovery opens up new avenues for exploring the cosmic processes that shaped the formation and evolution of stars.

Furthermore, LAMOST J1010+2358 exhibits a notably higher iron abundance ([Fe/H] = -2.42) compared to the majority of metal-poor stars found in the Galactic halo. This disparity suggests that the second-generation stars formed within the gas influenced by pair-instability supernovae (PISNe) might possess higher metal content than previously anticipated. The finding challenges existing assumptions and indicates that the chemical enrichment resulting from PISNe-dominated environments may have contributed to the increased metallicity observed in these second-generation stars. This insight broadens our understanding of stellar nucleosynthesis and the impact of primordial supernovae on the chemical evolution of the early universe.

Prof. Avi Loeb, former chair of the Astronomy Department at Harvard University, acknowledges the significance of discovering evidence for early pair-instability supernovae while emphasizing its importance in the search for metal-poor stars. Uncovering such evidence is considered a coveted achievement within the field, as it provides crucial insights into the understanding of stellar evolution, the early universe, and the role of pair-instability supernovae in shaping the cosmos. The pursuit of these findings is regarded as a significant milestone in expanding our knowledge of the universe's origins and its ongoing exploration.

Prof. Timothy Beers, the provost's chair of astrophysics at Notre Dame University, has expressed his perspective on the research outcomes. He highlights the significance of the paper, stating that it represents the first definitive correlation between a Galactic halo star and an abundance pattern that can be traced back to a pair-instability supernova (PISN). This achievement marks a significant milestone in our understanding of stellar astrophysics and further solidifies the link between metal-poor stars in the Galactic halo and the unique signatures left by PISNe. The research provides crucial insights into the origins and evolution of stars, enriching our understanding of the intricate processes that have shaped the universe.