The researchers found chemical evidence for a pair-instability supernova from the first very massive star

June 07, 2023

(Nanowerk News) The first stars illuminated the Universe during the Cosmic Dawn and ended the cosmic “dark ages” after the Big Bang. However, their mass distribution is one of the great unsolved mysteries of the cosmos.

Numerical simulations of the formation of the first stars estimate that the masses of the first stars were several hundred solar masses. Among them, the first stars with masses between 140 and 260 solar masses end up as instability-coupled supernovae (PISNe). PISNe is very different from ordinary supernovae (namely, Type II and Type Ia supernovae) and will imprint a unique chemical signature in the atmospheres of the next generation of stars. However, the signature was not found.

A new study led by Prof. ZHAO Gang of the National Astronomical Observatories of the Chinese Academy of Sciences (NAOC) has identified a chemically strange star (LAMOST J1010+2358) in the Galactic halo as clear evidence of the existence of a very massive PISNe. the first star in the early Universe, based on the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) survey and follow-up high-resolution spectral observations by the Subaru Telescope. This star is confirmed to have formed in a gas cloud dominated by the result of a 260 solar mass PISN.

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

This study was published online at Natural (“A metal-poor star with an abundance of a pair of instability supernovae”). Stellar fossils: traces of a pair of unstable supernovas from the first very massive stars. (Image: NAOC)

The research team made follow-up high-resolution spectroscopic observations of J1010+2358 with the Subaru telescope and obtained an abundance of more than ten elements. The most significant feature of this star is its extremely low abundance of sodium and cobalt. Its sodium-to-iron ratio is lower than 1/100 of the sun’s value. The star also shows great variation in abundance between elements with odd and even numbers of charges, such as sodium/magnesium and cobalt/nickel.

“The odd odd-even variation, together with the shortage of sodium and α elements in this star, is consistent with the primordial PISN prediction of a first generation star with a mass of 260 suns,” said Dr. XING Qianfan, the first author of learning.

The discovery of J1010+2358 is direct evidence of hydrodynamic instability due to the production of electron-positron pairs in the theory of the evolution of very massive stars. The creation of an electron-positron pair reduces thermal stress in the core of a very massive star and causes its partial collapse.

“This provides important clues for limiting the initial mass function in the early universe,” said Prof. ZHAO Gang, corresponding author of the study. “Prior to this study, no supernova evidence from such large stars was found in metal-poor stars.”

In addition, the iron abundance of LAMOST J1010+2358 ((Fe/H) = -2.42) is much higher than that of the most metal-poor stars in the Galactic halo, suggesting that second-generation stars that form in PISN-dominated gas may become even richer. metal than expected.

“One of the holy grails of the search for metal-poor stars is finding evidence of supernovas of these initial unstable pairs,” said Prof. Avi Loeb, former chair of the Department of Astronomy at Harvard University.

Prof. Timothy Beers, chair of astrophysics at the University of Notre Dame, commented on the results: “This paper presents what is, to my knowledge, the first definitive relationship of the Galactic halo stars to abundance patterns originating from the PISN.”

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