How did NASA’s Hubble Space Telescope study of the ages and metallicities of 39 globular clusters within the Milky Way’s inner 20,000 light-years provide evidence that the galaxy absorbed the dwarf galaxy Low-energy-Kraken-Heracles (LKH)—which contained about 500 million solar ma

Why this identifies LKH: The inferred time of the intermediate sequence marks when its parent system was absorbed: roughly 11.8 billion years ago. The number and properties of its surviving clusters imply a dwarf galaxy with about 500 million solar masses in stars—large enough to have been a consequential early building block, not a minor stellar stream.

A timing nuance: “About 2 billion years after the Big Bang” is a rounded public description. The paper’s preprint frames the event as roughly 1.5 billion years after the Big Bang; either way, it occurred at an exceptionally early epoch and extends the securely reconstructed merger history of the Milky Way by about 1.8 billion years.

What it says about Milky Way assembly: The result supports a hybrid picture. The early Milky Way formed some of its oldest clusters internally, but it also grew rapidly through external accretion; a major early merger likely added stars, clusters, gas, and dynamical disturbance that helped shape subsequent evolution. It does not mean that all early Milky Way stars were accreted—rather, both in-situ formation and hierarchical merging were important.

Why this is galactic archaeology: Rather than observing the destroyed dwarf directly, researchers reconstruct it from surviving cluster ages, chemical histories, and orbital/dynamical information. The LKH result demonstrates that globular-cluster age–metallicity distributions can preserve evidence of mergers whose ordinary stellar debris has become too mixed to recognize cleanly.

Connection to the 2026 Kavli Prize: Vasily Belokurov, Amina Helmi, and Rodrigo Ibata received the 2026 Kavli Prize in Astrophysics for uncovering fossil evidence of past mergers and demonstrating that the Milky Way was built through hierarchical accretion. LKH is a new, concrete example of the kind of reconstruction that this field—and that recognition—celebrates.

What future Hubble work could find: Observations of previously unstudied, especially obscured inner-Galaxy globular clusters could reveal additional discrete age–metallicity sequences. That could expose other ancient, now fully disrupted progenitor galaxies, refine their masses and merger dates, or test whether apparent cluster groups are truly separate mergers rather than extensions of LKH, GSE, or the native Milky Way sequence. Specific additional mergers cannot yet be identified from the current evidence.