Group of ancient stars spotted near the sun could rewrite the history of the Milky Way

Ancient stars located surprisingly close to our sun formed less than a billion years after the big Bang — suggesting that part of the Milky Way is much older than previously thought, a study has found.

Most of the stars, including the sunThey are located in a thin disk rotating around the center of the galaxy. Researchers thought this disk formed about 8 to 10 billion years ago, but with the help of machine learning, they discovered that some of its stars are more than 13 billion years old.

Researchers dated these ancient stars by studying data collected by the European Space Agency Gaia spacecraft and published their findings in preprint arXiv server earlier this year. The Leibniz Institute for Astrophysics Potsdam (AIP) in Germany announced the discovery on Wednesday, July 31.

The universe is about 13.8 billion years old, so the presence of 13-billion-year-old stars in our galaxy’s thin disk means the disk must have formed within the first billion years after the universe’s birth — greatly delaying our galaxy’s star formation schedule.

“These ancient stars in the disk suggest that the formation of the Milky Way’s thin disk began much earlier than previously believed, about 4 to 5 billion years ago,” said the study’s lead author. Samir Nepala doctoral candidate studying the Milky Way at AIP, said in a declaration.

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This map highlights the different ages of the stars surrounding our sun, marked in orange. Blue stars are young and red stars are old. (Image credit: Background image by NASA/JPL-Caltech/R. Hurt (SSC/Caltech))

Scientists are piecing together the history of the Milky Way with data from Gaia to create maps that document the age, chemical composition and motion of its stars, according to the statement. The Milky Way contains over 100 billion stars, so there’s a lot to map.

For the new study, the researchers looked at more than 800,000 stars in the solar neighborhood, which runs about 3,200 light-years around the sun; for comparison, the entire Milky Way galaxy is about 100,000 light-years wide. The team used machine learning to combine different data, giving measurements for variables like the stars’ age and metal content. This data revealed that most of these stars were more than 10 billion years old, and some were more than 13 billion years old.

The metal content of the stars is also surprising. Old stars are typically very poor in metals because they formed when the universe was mostly hydrogen and helium. However, some of the ancient stars in the study were metal-rich, with twice the amount of metals compared to our youngest, 4.6-billion-year-old sun. These results indicate that there was a rapid enrichment of metals in the early stages of our galaxy, according to the statement.

“This study also highlights that our galaxy had intense star formation at early times, which led to very rapid metal enrichment in the inner regions and the formation of the disk,” said Nepal.

Gaia has uncovered many secrets about the history of our galaxy, including previously unknown mergers with other galaxies and remnants of the first building blocks of the Milky Way. The spacecraft briefly stopped returning usable data after a small meteoroid impact earlier this year, but is now back in working order and is expected to continue its mission until the end of 2025.

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