During the Cosmic Dawn, the first stars emerged and brought an end to the cosmic “dark ages” that followed the Big Bang. However, understanding the distribution of their mass remains a perplexing puzzle in the realm of astrophysics.
Scientific simulations aimed at comprehending the formation of these early stars suggest that their mass could reach several hundred times that of our Sun. Among this population, stars with masses ranging from 140 to 260 solar masses were believed to undergo pair-instability supernovae (PISNe). These unique events differ significantly from regular supernovae, such as Type II and Type Ia, and would have left behind distinctive chemical imprints in the subsequent generation of stars. Surprisingly, no such signature had been detected until now.
A groundbreaking study, led by Professor Zhao Gang from the National Astronomical Observatories of the Chinese Academy of Sciences (NAOC), has identified a chemically unusual star named LAMOST J1010+2358 in the Galactic halo. This finding provides clear evidence for the existence of PISNe originating from the incredibly massive first stars in the early universe. The discovery was made possible through the utilization of the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) survey, combined with subsequent high-resolution spectroscopic observations using the Subaru Telescope. Collaborating researchers from the Yunnan Observatories of CAS, the National Astronomical Observatory of Japan, and Monash University in Australia contributed to this significant breakthrough.
To further investigate LAMOST J1010+2358, the research team conducted follow-up observations using the Subaru telescope, obtaining detailed spectra for over ten elements. The most remarkable characteristic of this star lies in its remarkably low sodium and cobalt abundances. In fact, its sodium-to-iron ratio is less than 1/100 of the solar value. Additionally, the star displays a substantial disparity in abundance between elements with odd and even charge numbers, such as sodium/magnesium and cobalt/nickel.
This groundbreaking study, published in the esteemed journal Nature, sheds light on the chemical anomalies associated with PISNe, confirming that LAMOST J1010+2358 was indeed formed within a gas cloud enriched by the yields of a 260 solar mass PISN.
Dr. Xing Qianfan, the primary author of the study, emphasized, “The distinctive variations between odd and even elements, coupled with the sodium and α-element deficiencies in this star, align perfectly with the anticipated outcomes of primordial PISNe arising from first-generation stars with masses of 260 solar masses.”
The identification of J1010+2358 serves as concrete proof of the hydrodynamical instability resulting from electron-positron pair production during the evolution of extremely massive stars. The formation of electron-positron pairs diminishes thermal pressure within the core, triggering a partial collapse.
“This discovery provides a crucial clue in the effort to determine the initial mass function in the early universe,” stated Prof. Zhao Gang, the corresponding author of the study. “Until now, no evidence of supernovae originating from such massive stars had been detected in metal-poor stars.”
Furthermore, the iron abundance of LAMOST J1010+2358 ([Fe/H] = -2.42) surpasses that of the most metal-poor stars within the Galactic halo. This suggests that second-generation stars formed in gas predominantly influenced by PISNe might possess higher metallicity than initially presumed.
Prof. Avi Loeb, the former chair of the Astronomy Department at Harvard University, hailed the discovery as “one of the long sought-after achievements in the search for metal-poor stars: finding tangible evidence of these early pair-instability supernovae.”
Commenting on the results, Prof. Timothy Beers, the provost’s chair of astrophysics at Notre Dame University, stated, “To the best of my knowledge, this paper presents the first definitive association between a Galactic halo star and an abundance pattern originating from a PISN.”
Source: Chinese Academy of Sciences