Science Gazette

A new database of tens of millions of stars reveals the Milky Way’s chemical past

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Researchers have released a new sample catalog including over 24 million stars that may be used to deduce the chemical history of elements in the Milky Way galaxy.

Researchers at the University of Notre Dame have released a new sample catalog of more than 24 million stars that may be used to analyze the chemical history of elements in the Milky Way Galaxy with partners from China and Australia.

The study, which was published in The Astrophysical Journal this month, represents approximately one-hundredth of one percent of the Milky Way’s 240 billion stars. It’s a watershed moment for Timothy Beers, Notre Dame’s Grace-Rupley Professor of Physics, who has spent his career organizing and conducting ever-larger surveys of stars to interpret the galaxy’s creation and chemical development, a study known as galactic archaeology. Researchers used a novel method to calculate the abundances of heavy elements like iron by measuring the light from each star. Their distances, movements, and ages were also recorded.

“From when the Milky Way galaxy first started to generate stars soon after the Big Bang until the present,” Beers said, “the elements abundances of individual stars track the chemical enrichment of the Milky Way galaxy.”

“We can restrict the origin of various components in the galaxy, such as the halo and disk populations, by combining this knowledge with star distances and movements,” he said. “Putting an age estimate on the process gives it a ‘clock,’ allowing for a far more comprehensive image of the whole process to be constructed.”

Beers and partners’ previous spectroscopic work gave the data for the tens of thousands of stars necessary to calibrate the new technique, which is based on precision photometric observations. To calibrate estimates of metallicity, researchers utilized extensive photometric samples collected with the Australian SkyMapper Southern Survey and the European Gaia satellite project.

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Until recently, the only way to get precise estimates of the abundance of heavy metals like iron in a large number of stars was to take low- and medium-resolution spectra that could be examined to extract this data. It was a lengthy and arduous procedure.

Beers is primarily interested in stars with the lowest metallicities — extremely metal-poor stars with iron abundances less than 1% that of the sun — since they formed early in the universe’s history and hence show the genesis of elements in the periodic table. When Beers began his study in the early 1980s, there were only approximately 20 highly metal-poor stars known. This latest catalog takes the total number of “night sky fossils” collected by Beers to over 500,000.

The new catalog, which contains more than 19 million dwarf and five million big stars, is anticipated to increase understanding of how the Milky Way was generated in a number of ways, according to Beers. Characterizing the structure of galaxy thin/thick disks — spiral galaxies’ structural components — as well as the population of stars and globular clusters that surround most disk galaxies, known as the stellar halo, are among them. The star catalog will also aid astronomers in locating star trails left by broken dwarf galaxies and globular clusters.

Other collaborators include lead author Yang Huang of Yunnan University in China; Christian Wolf and Christopher A. Onken of Australian National University; Young Sun Lee of Chungnam National University in Korea; Haibo Yuan of Beijing Normal University, China; Huawei Zhang of Peking University, China; Chun Wang of Tianjin Normal University, China; and Jianrong Shi and Zhou Fan of the Chinese Academy of Sciences.

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The work of Beers and Shank on this study was funded by the National Science Foundation’s grant 14-30152, Physics Frontier Center/JINA Center for the Evolution of the Elements (JINA-CEE). Beers was also recognized by the Chinese Academy of Science with a 2019 PIFI Distinguished Scientist award.

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