Old stars discovered within our Milky Way galaxy might be among the universe's oldest ever to exist

Smaller star systems may have originated from their own mini galaxies that got engulfed by the Milky Way in the past.

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2025 September 16 . 5:52 AM

2 min read

Old Stars Discovered Within Our Galaxy May Possess Ancient Cosmic Origins

Old stars discovered within our Milky Way galaxy might be among the universe's oldest ever to exist

In a groundbreaking discovery, a new way to find ancient stars has been uncovered, offering valuable insights into the early stages of galaxy formation and evolution. These stars, collectively known as the SASS (Small Accreted Stellar System) stars, have been found to be part of the cosmic family tree, having once belonged to their own small galaxies that were later absorbed by the Milky Way.

Each star within the SASS group exhibits rapid motion, suggesting they started life outside the Milky Way, likely in primitive dwarf galaxies that later fell into our own. The dwarf galaxies themselves, however, are too faint to be studied in detail.

The SASS stars are significant as they are moving very quickly and in the opposite direction to most other stars in the Milky Way. This rapid motion, combined with their ancient origins, makes them likely remnants of primitive dwarf galaxies.

Anna Frebel from MIT led the study and stated that brighter SASS analogues in the Milky Way can now be studied for their chemical evolution. The heavy elements within these stars suggest they formed very early in the Universe, soon after the Big Bang, and the amount of heavy elements indicates they formed around 12-13 billion years ago.

The discovery of SASS stars provides a new opportunity to study the chemical evolution of stars in the Milky Way. As these ancient stars produced heavier elements, which were incorporated into subsequent generations of stars, they offer a unique window into the early Universe.

Though part of the Milky Way, the SASS stars were likely part of different galaxies before being absorbed. The team behind the study has named the stars 'SASS', meaning Small Accreted Stellar System stars. These ancient stars, moving quickly in the opposite direction of most Milky Way stars, are considered part of the cosmic family tree, offering valuable insights into the history and evolution of the Milky Way and the Universe as a whole.