Discovery of ancient stars near the Sun could rewrite the history of the Milky Way

A new study has revealed that the Milky Way’s thin disk could be much older than previously thought, thanks to the discovery of ancient stars surprisingly close to our sun. Researchers using data from the European Space Agency’s Gaia space telescope have found that some of these stars formed less than a billion years after the Big Bang, making them more than 13 billion years old.

This discovery challenges the long-held belief that the Milky Way’s thin disk, where most stars including the Sun are located, formed about 8 to 10 billion years ago. Instead, the new findings suggest that the formation of this region of the Milky Way began 4 to 5 billion years earlier than previously thought. This significant revision of the timeline could dramatically change our understanding of the history and evolution of the Milky Way.

The researchers, led by Samir Nepal, a PhD candidate at the Leibniz Institute for Astrophysics Potsdam (AIP) in Germany, dated these ancient stars using advanced machine learning techniques. By analyzing data collected by the Gaia spacecraft, the team was able to estimate the ages and metal content of more than 800,000 stars in the solar neighborhood, a region stretching about 3,200 light-years around the sun. The results, posted to the pre-print arXiv server and announced by AIP on July 31, show that many of these stars are more than 10 billion years old, with some even older than 13 billion years.

The presence of such old stars in the thin disk of the Milky Way is a surprising and intriguing find. Given that the universe itself is about 13.8 billion years old, the existence of these stars suggests that this part of our galaxy must have formed very early in the history of the universe, within the first billion years after the Big Bang.

The study highlights an unexpected aspect of these old stars: their metal content. Stars that formed in the early universe are metal-poor because they were created when the universe was mostly hydrogen and helium.