Milky Way's Disk Grew 'Upside Down': Younger Stars Form in Thinner Layers, New Study Reveals

A new study reveals that the Milky Way's disk grew 'upside down,' with younger stars forming in progressively thinner layers over billions of years. Researchers analyzed data from the European Space Agency's Gaia mission and the LAMOST survey, finding that stars in the thick disk are older and have higher metallicity, while stars in the thin disk are younger and more metal-poor. This pattern suggests that the galaxy's star formation rate declined over time, leading to a thinner disk. The findings, published in Nature Astronomy, provide new insights into the Milky Way's evolutionary history and the processes that shaped its current structure. The study's lead author, Dr. Maosheng Xiang from the Max Planck Institute for Astronomy, notes that this 'upside-down' growth challenges previous models of galaxy formation. Understanding how our galaxy assembled can help astronomers piece together the history of the universe and the formation of other spiral galaxies.