Researchers from the Massachusetts Institute of Technology discovered three of the oldest stars in the universe that are located in the neighborhood of the Milky Way, the magazine reported Monthly Notices of the Royal Astronomical Society (MNRAS).
The oldest stars are found in the Milky Way's halo, a thin cloud of stars and gas that surrounds the galactic disk. According to the team's analysis, the three stars formed 12-13 billion years ago. They are grouped together in a group called SASS (small accreted star system), indicating that each star once belonged to a small, primitive galaxy swallowed up by the growing Milky Way.
SASS originated shortly after the Big Bang 13.8 billion years ago, when the universe consisted mostly of hydrogen and helium and very small amounts of other chemical elements such as strontium and barium. These ancient stars have roughly the same composition.
Thus, studying SASS could be key to understanding the evolution of ancient ultra-faint dwarf galaxies. All three stars are located in different places in the halo, but their distance from Earth is about 30 thousand light years (about a third of the diameter of the disk of the Milky Way).
Their motion occurs in the opposite direction to the rest of the galactic disk, which, together with their unusual chemical composition, indicates that they did not originally belong to the Milky Way.