Overview
- The peer-reviewed paper, which was published Monday, combines deep Hubble imaging with Gaia astrometry to measure ages, chemical abundances and orbits of 39 globular clusters in the inner 20,000 light-years and finds a distinct cluster family.
- The team calls the accreted dwarf Low-energy–Kraken–Heracles (LKH) and estimates it had about 500 million solar masses in stars when it merged with the Milky Way roughly 11.8 billion years ago, about 1.8–2 billion years before the Gaia–Sausage–Enceladus event.
- Researchers used globular clusters as long-lived fossil records because their stars retain precise ages and metallicities, which allowed the authors to separate native Milky Way clusters, GSE clusters, and a third population tied to LKH.
- The authors argue LKH likely delivered stars, gas plus dark matter that could have driven bursts of star formation in the infant Galaxy, but they stress the result applies strongest to the sampled inner region and needs wider spatial coverage for full validation.
- Next steps include expanded Hubble cluster surveys, deeper infrared observations to peer through dust, and simulations to test how broadly LKH influenced the Milky Way's early structure and chemical evolution.