Beijing, June 6 (Reporter Sun Zifa) An international team led by researcher Zhao Gang of the National Astronomical Observatory of the Chinese Academy of Sciences (CAS) was the first to find chemical evidence for the existence of "unstable supernova" (PISN) formed by the evolution of the first generation of supermassive stars in the silver halo star. Their research confirmed that the particular supernova originated from a first-generation star with a mass of up to 8 times the mass of the sun, refreshing the understanding of the mass distribution of the first generation of stars.
This important astronomical discovery and research result paper was published online in the internationally renowned academic journal Nature on June 6, and Chinese and foreign astronomers paid great attention to it, and commented that the achievement was of great significance and far-reaching impact on the study of star origin and the evolution of the Milky Way.
Proof of the existence of stars in the early universe with more than 100 solar masses
Academician Han Zhanwen of the Yunnan Astronomical Observatory of the Chinese Academy of Sciences pointed out that after the Big Bang, the first generation of stars formed, and they were composed only of hydrogen and helium. Through nuclear fusion and supernova explosions, the first generation of stars created new elements, the first step in making up colorful worlds. Understanding the nature of first-generation stars is critical to understanding the formation of stars, galaxies, and the large-scale structure of the universe.
Han Zhanwen said that in the past few decades, scientists around the world have been searching for the first generation of stars. After unremitting efforts, the astronomical abundance and galaxy evolution team of the National Astronomical Observatory of the Chinese Academy of Sciences discovered early stars from the survey data of the Guo Shoujing Telescope (Large Sky Area Multi-target Fiber Spectroscopic Astronomical Telescope, abbreviated as LAMOST), and accurately measured its elemental abundance using the Japanese Pleiades telescope (Subaru). They found the abundance of characteristic elements produced by the first generation of stars "for unstable supernovae" explosions. This is the clearest evidence of such supernovae ever discovered, proving that in the early universe, stars more than 100 times the mass of the sun did indeed exist.
One of the most important achievements of the last decade in the study of the first generation of stars
Tim Beers, a professor at the University of Notre Dame, believes that the astronomy paper published in Nature is one of the most important results in the field of first-generation stellar research in the past decade, and "we have also been searching for stars that retain the characteristics of first-generation stars." Astronomers generally agree that stars are difficult to form in environments containing only hydrogen and helium because gases take a long time to cool in environments lacking metals (astronomically called metals other than hydrogen and helium). Supermassive stars forming in the universe must be very massive to form when the gas cools down enough. These supermassive stars are so rare that no observational evidence has ever been found before this paper.
Such supermassive stars are short-lived, ending as supernovae in about a few million years, leaving a special chemical imprint. Theorists, including some of the paper's authors, predicted that stars with masses higher than 150 times the mass of the sun might leave such unique imprints, but these imprints had never been definitively discovered before the paper.
The first generation of supermassive stars evolved into an artistic display of "unstable supernovae". Photo courtesy of the National Astronomical Observatory of the Chinese Academy of Sciences
It will reveal unknown mechanisms for the formation of supermassive black holes
Professor Kazumitsu Aoki of the National Astronomical Observatory of Japan has been using the massive spectral data of the Guo Shoujing telescope for the past ten years to search for very old stars born in the early Milky Way, and using the Pleiades telescope to confirm the chemical composition of these stars, and finding evidence of the existence of the first generation of supermassive stars is a major goal of their research project. He said that the star found in this study has a very unique elemental abundance, providing the clearest evidence of the supernova explosion of the first generation of supermassive stars.
Toshiki Kajino, a Japanese professor at Beihang University and an expert in cosmology and theoretical nuclear astrophysics, worked with Chinese astronomers for more than a decade based on Guo Shoujing's telescope survey data when he worked at the University of Tokyo and the National Astronomical Observatory of Japan. He believes that this discovery, and many future discoveries, will reveal unknown mechanisms for the formation of supermassive black holes in the early universe.
Having witnessed the successful cooperation between the Guo Shoujing telescope in China and the telescope in the Pleiades in Japan for many years, "I would like to say that today's achievement is the result of the cooperation of this international team." The Japan-China Telescope Collaboration is now at the forefront of spectroscopic observations in the international astronomical community, "and we look forward to more major discoveries by Asian astronomers." Toshiki Kajino said.
For the first time, key evidence of an explosion "against an unstable supernova" was given
Wang Xiaofeng, a professor in the Department of Physics at Tsinghua University, said that the elements synthesized during the evolution of the star and the heavier elements formed during the explosion are ejected into interstellar space during the supernova explosion, thereby greatly changing the material composition of the interstellar gas around the explosion star. These gases are polluted by the heavy elements ejected by supernova explosions and become much higher than the previous metal content, and the gas re-condenses under the action of gravity to form a new generation of stars and therefore has a higher metal content, they carry the elemental imprint formed by the evolution and explosion of the parent star. These elemental imprints can help trace the nature of their parents' stars and the physical mechanisms by which they erupted and died. "It's like we can trace the characteristics of a child's parents by looking up their DNA."
Wang Xiaofeng pointed out that the extremely metal-poor star numbered LAMOST J1010+2358 discovered by Zhao Gang's research team is very different from the metal element distribution characteristics of other known metal-poor stars, and these differences cannot be explained by the model of the collapse explosion of the father's star, and the analysis shows that its previous generation of stars belongs to the first generation of stars that have undergone "unstable supernova" explosions.
He said that this study gives the first key evidence that massive stars in the early universe have experienced "unstable supernova" explosions, and is of great significance for validating supernova explosion models and limiting the theory of star formation in the early universe.
Astronomical observations often bring unexpected surprises
Researcher Zhao Gang emphasized that the discovery of the chemical remains of the first generation of supermassive stars, although it is not very closely related to astronomers' original idea of studying the formation of the Milky Way, but it is crucial to the chemical evolution of the Milky Way. The chemical evolution of the Milky Way is one of the important research directions of his research team, which can reproduce the chemical evolution of the Milky Way by observing and analyzing the elemental abundance of stars of different ages.
If the mass distribution of stars is now observable, the results of current observations cannot be given by calculations from the chemical evolution model of galaxies. To solve this problem, theoretical astrophysicists have proposed the hypothesis that the first generation of stars formed after the Big Bang were mainly supermassive stars, which could be quickly synthesized into abundances consistent with the various elements observed today. Their detailed calculations of the evolution and nucleosynthetic yields of various massive and supermassive stars have led many observational astronomers to search for evidence of the existence of such supermassive stars, which has not been found until now.
"The crowd looked for him a thousand degrees, and looked back, but the man was in the lamplight." Zhao Gang quoted the classic phrase of ancient Chinese poetry as saying that astronomical observations often bring people unexpected surprises and are exciting. As for whether this important astronomical discovery was an unexpected surprise or the achievement of a goal that had been predetermined for many years, he believed that there were both expected and unexpected surprises, which is also the enduring charm of astronomy. (End)