The oldest thin disk stars in the Milky Way formed about 9.50 billion years ago

　　Science and Technology Daily, Beijing, March 2 (Reporter Lu Chengkuan) The reporter learned from the National Astronomical Observatory of the Chinese Academy of Sciences on the 2nd that based on the observation data of Guo Shoujing Telescope and Kepler Space Telescope, our country astronomers found that the earliest known stars in the Milky Way’s thin disk are about 9.50 billion years old. This provides an important observational basis for a deep understanding of the early formation and evolution history of the Milky Way’s thin disk. The relevant research results were published in the Monthly Journal of the Royal Astronomical Society.

　　Astronomers generally agree that the main characteristic structures of the Milky Way include the central bulge, the Milky Way disk, and the Milky Way halo. Among them, the Milky Way disk includes the thick disk and the thin disk. The thick disk stars formed before the thin disk stars, that is, the thin disk is younger than the thick disk. The formation of the thin disk is a very important event that has occurred in the Milky Way in the past about 8 billion years.

　　So what exactly happened when the thin and thick disks formed? When did the earliest thin disk stars form? "These questions have puzzled astronomers, and the key to solving them lies in obtaining accurate age samples of galactic disk stars," said Wu Yaqian, the lead author of the paper and an associate researcher at the National Astronomical Observatory of the Chinese Academy of Sciences.

　　Starseismology is considered one of the most accurate ways to determine the age of stars. Because red giants are relatively bright, astronomers typically use these red giants, which are scattered across the galactic disk, as probes to track them farther into the galactic disk.

　　In this study, the researchers accurately determined the age of 5,306 red giant stars. On this basis, the researchers used chemical methods to distinguish between thin and thick disk stars, and systematically studied the distribution of the age of the thin disk stars in the galactic disk. The oldest thin disk stars were found to be about 9.50 billion years old.

　　"This result is more consistent with the theoretical expectation of the’double infall ‘model of the Milky Way disk; at the same time, the Milky Way’s thick disk is still forming stars during this time, indicating that there is a common time window for the formation of thin and thick disk stars in the Milky Way," Wu Yaqian explained.

　　In addition, the study also found that the metallicity distribution and spatial distribution of the first thin disk stars were extensive, suggesting that inner and outer disk stars in thin disk stars may have formed simultaneously.