In a groundbreaking study, scientists have found direct evidence of the primordial pair-instability supernovae in a star’s unique chemical composition. This finding reveals fascinating aspects of very massive star evolution, offering valuable clues to the cosmic landscape during the universe’s infancy.
During the Cosmic Dawn, the Universe witnessed the emergence of its first stars, bringing an end to the cosmic “dark ages” that followed the Big Bang. However, the distribution of their mass remains a profound enigma within the realm of cosmology.
According to numerical simulations depicting the formation of these primordial stars, their mass is estimated to have reached several hundred times that of our Sun. Among these stellar entities, those with masses ranging from 140 to 260 times that of the Sun culminated in pair-instability supernovae (PISNe). These unique events differ significantly from regular supernovae, such as Type II and Type Ia, and would have left a distinctive chemical signature in the atmosphere of subsequent generations of stars. Curiously, no such signature had been discovered until now.
In a groundbreaking study led by Professor ZHAO Gang from the National Astronomical Observatories of the Chinese Academy of Sciences (NAOC), a chemically distinct star known as LAMOST J1010+2358, found in the Galactic halo, has been identified as compelling evidence for the existence of PISNe originating from exceptionally massive first stars in the early Universe. This remarkable revelation is based on data obtained from the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) survey, supplemented by high-resolution spectroscopic observations from the Subaru Telescope.
The research team behind this remarkable achievement includes scientists from the Yunnan Observatories of the Chinese Academy of Sciences, the National Astronomical Observatory of Japan, and Monash University in Australia.
The findings of this study were just published online in the esteemed journal Nature, cementing its significance in the field of astrophysics.
The research team has diligently conducted follow-up observations of J1010+2358 using the advanced Subaru telescope, employing high-resolution spectroscopy to derive abundances for more than ten different elements. The star’s most notable characteristic lies in its remarkably low levels of sodium and cobalt. In fact, its sodium-to-iron ratio is less than 1/100th of the solar value. Furthermore, this star exhibits a significant disparity in abundance between elements with odd and even charge numbers, such as sodium/magnesium and cobalt/nickel.
Dr. XING Qianfan, the study’s first author, remarked, “The peculiar odd-even variance, along with deficiencies of sodium and α-elements in this star, are consistent with the prediction of primordial PISN from first-generation stars with 260 solar masses.”
The discovery of J1010+2358 serves as direct evidence for the hydrodynamical instability resulting from electron-positron pair production during the evolution of immensely massive stars. The creation of electron-positron pairs diminishes thermal pressure within the core of these stars, triggering a partial collapse.
“It provides an essential clue to constraining the initial mass function in the early universe,” added Prof. ZHAO Gang, corresponding author. “Before this study, no evidence of supernovae from such massive stars has been found in the metal-poor stars.”
Additionally, the iron abundance of LAMOST J1010+2358 ([Fe/H] = -2.42) surpasses that of most metal-poor stars found in the Galactic halo. This discrepancy suggests that second-generation stars formed in gas dominated by PISNe may possess greater metallic content than previously anticipated.
“One of the holy grails of searching for metal-poor stars is to find evidence for these early pair-instability supernovae,” commented Prof. Avi Loeb, former chair of the Astronomy Department at Harvard University.
“This paper presents what is, to my knowledge, the first definitive association of a Galactic halo star with an abundance pattern originating from a PISN,” commented Prof. Timothy Beers, the provost’s chair of astrophysics at Notre Dame University.
Source: 10.1038/s41586-023-06028-1
Image Credit: NAOC