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SDSS J001820.5–093939.2 or SDSS J0018-0939 for short is a star system approximately 1000 light-years away near the constellation Cetus. SDSS J0018-0939 is a cool main-sequence star. It is the first star found proposed to be a massive second generation star. ==Background== Theory and computer simulations predicted the formation of massive stars, from gas clouds containing only hydrogen and helium, within a few hundred million years after the Big Bang . The first massive stars died in supernova explosions which ejected heavier elements into the gas, that formed the next generations of stars. The element composition of a star is an indirect indication of the star's generation and its previous star generation. The mass distribution of the first generation stars is key to understanding the formation of the Universe's structure, chemical enrichment, and large stellar structures like galaxies. No evidence of supernovae from the very massive first generation stars has been found in the chemical composition of the Milky Way stars. Stars with mass less than the Sun's mass, have very long lifetimes, long enough to be discovered. The distinctive chemical patterns of these low mass stars can be used to estimate the mass of the first generation stars. In the past thirty years astronomers have conducted large-scale investigations to find low-mass and metal-poor stars formed in the early Universe.〔 〕 The Sloan Digital Sky Survey (SDSS) and Sloan Extension for Galactic Understanding and Exploration (SEGUE) projects are the latest to obtain evidence for the age, chemical composition and distribution of stars in the Milky Way, and provided crucial clues to understand the structure, formation and evolution of the Milky Way Galaxy. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「SDSS J001820.5-093939.2」の詳細全文を読む スポンサード リンク
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