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4w ago

Astronomers Find 20 Very‑Metal‑Poor Stars Near Milky Way Disk and Propose a Lost Dwarf Galaxy

The team says shared chemical fingerprints and mixed orbits point to an early merger that could add a missing piece to the galaxy’s formation story.

This image visualizes the Milky Way and its surrounding halo of stars, some of which originated from past mergers.
An artist's impression depicts the Milky Way based on data from the Gaia telescope.
Gaia's mapping shows how 40,000 stars, all located within 326 light-years of the solar system, will move in the next 400,000 years.
Data from more than 1.8 billion stars have been used to create this map of the Milky Way as captured by Gaia.

Overview

  • A study published in Monthly Notices of the Royal Astronomical Society reports 20 very‑metal‑poor stars about 7,000 light‑years from the Sun that lie unusually close to the Milky Way’s disk.
  • Researchers used Gaia astrometry to select candidates and high‑resolution spectroscopy from the Canada‑France‑Hawaii Telescope to show the stars share nearly identical chemical abundances, suggesting a common origin.
  • The stars split between prograde and retrograde orbits, a pattern the authors say fits debris from a single dwarf galaxy they nickname 'Loki' that was accreted early in the Milky Way’s history.
  • Other astronomers call the chemical‑fingerprint method powerful but caution the claim is tentative because the group could be part of a known structure and larger samples and independent tests are needed.
  • If confirmed, the finding would reveal a previously hidden merger event that could change models of how the Milky Way grew and highlights the value of combining Gaia maps with follow‑up spectroscopy to find ancient stellar fossils.