Scientists Identify 12.3-Billion-Year-Old LKH Merger With 5×10^8-Solar-Mass Galaxy
Updated
Updated · Nature.com · Aug 17
Scientists Identify 12.3-Billion-Year-Old LKH Merger With 5×10^8-Solar-Mass Galaxy
3 articles · Updated · Nature.com · Aug 17
Summary
A new analysis of 39 Milky Way globular clusters found a distinct third age-metallicity sequence, pointing to a major merger about 12.3 billion years ago—roughly 1.8 billion years before Gaia-Sausage-Enceladus.
Hubble Space Telescope data and a Bayesian chrono-dynamical model let researchers date clusters to within a few hundred million years, separating 12 inner-galaxy clusters from both the Milky Way’s own population and GSE.
The newly named Low-energy-Kraken-Heracles progenitor appears to have had a stellar mass near 5×10^8 solar masses, similar to GSE, and deposited most of its material within the Milky Way’s inner 6 kiloparsecs.
The result strengthens the case that earlier disputed 'Kraken' globular clusters and the debated Heracles stellar population trace the same ancient accretion event, helping settle a long-running argument over the inner Galaxy’s origins.
Researchers said the finding pushes the Milky Way’s firmly reconstructed merger history beyond 10 billion years and suggests future stellar-age measurements from Gaia-based work and PLATO could map its first billion years in finer detail.
Could the Milky Way's oldest star clusters actually be internal anomalies rather than the remains of a devoured galaxy?
What other ancient, ghostly galaxies might still be hiding deep within the heart of our Milky Way?
How did a violent galactic collision 11.8 billion years ago secretly pave the way for our solar system's existence?
The LKH Merger: Unveiling the Milky Way’s Earliest Major Collision 12 Billion Years Ago
Overview
In August 2026, scientists discovered that the Milky Way collided with the LKH dwarf galaxy about 12 billion years ago, pushing back the timeline of our galaxy’s major mergers by 1.8 billion years and overturning the old idea that the Milky Way grew only from its own stars. By combining Hubble and Gaia data, researchers identified a unique group of globular clusters from this ancient merger. The collision’s gravitational shock heated and thickened the early disk, while the Milky Way absorbed low-metallicity gas, causing a temporary drop in heavy elements and delaying rocky planet formation. Later, supernovae from a starburst restored and increased the metallicity, enabling widespread planet formation.