Hubble confirms Milky Way swallowed a tiny galaxy in its first two billion years
The Hubble Space Telescope has detected definitive evidence that the Milky Way swallowed a dwarf galaxy named LKH 11.8 billion years ago, revealing a previously unknown merger from the earliest epochs of galactic assembly.
NASA’s Hubble Space Telescope has identified definitive evidence that the Milky Way engulfed a small companion galaxy roughly 11.8 billion years ago, revealing the Low-energy-Kraken-Heracles merger as a major event in the galaxy’s first few billion years the detection relied on analysis of 39 globular clusters to confirm that age-metallicity sequencing proved captured members belonged to a swallowed dwarf system, per findings published in Nature Astronomy on August 17, 2026. The merger occurred about two billion years after the Big Bang, placing the event firmly within the earliest epochs of galactic evolution rather than among the later collisions astronomers have previously cataloged. By examining the chemical signatures preserved in these cluster populations, researchers could distinguish stars that formed inside the Milky Way from those brought in by the LKH galaxy, reconstructing a collision that shaped the core structure of our local cosmic neighborhood.
The age-metallicity sequencing analysis that confirmed the merger relies on treating globular clusters as chemical fossils rather than mere gravitational tracers. When a larger galaxy consumes a dwarf companion, it absorbs not only the dwarf’s stars but also the dense star clusters orbiting within it, preserving the accreted system’s unique elemental composition and formation age across the host’s halo. Researchers focused on specific populations within the 39 confirmed clusters to isolate those that break from the Milky Way’s native formation curve, identifying groups whose chemical signatures betray an origin independent of our current galactic disk. This approach allowed astronomers to verify the merger by finding surviving stellar material from the accreted system still bound to the Milky Way, rather than relying solely on theoretical models.
Placing the LKH event 11.8 billion years ago shifts the understanding of the Milky Way’s assembly window significantly forward into the universe’s youth. The timing indicates that our galaxy was already active in major mergers roughly two billion years after the Big Bang, a period when structure formation across the cosmos was still rapid but distinct from the later buildup of massive galaxies. Hubble’s data verify that the LKH collision happened approximately 1.8 billion years before the widely studied Gaia-Sausage-Enceladus merger, a previously unknown event that extends the timeline of Milky Way assembly back nearly two billion years before the next most significant documented impact. That interval suggests the galaxy underwent its most critical phase of growth during a period that had previously been inferred but never proven, moving astronomers from reconstructing the Milky Way’s second act to documenting its opening pages.
The contrast between the newly confirmed LKH merger and the better-documented Gaia-Sausage-Enceladus collision highlights how much of a galaxy’s infancy can remain obscured by distance and time. While the Sausage merger occurred later in the galaxy’s life cycle, bringing significant material into the solar neighborhood after the halo had largely formed, the LKH event predates that influence by a comparable margin with a much younger host. The discovery confirms that the Milky Way did not simply expand quietly before facing more recent structural upheavals; instead, it was actively consuming smaller systems and integrating them into its forming halo almost immediately after its own genesis. Recognizing this earliest merger forces a revision of the sequence by which the Milky Way grew, positioning the swallowing of LKH as the foundational event upon which all subsequent structural changes would be built.
Identifying the chemical and age markers of a dwarf system swallowed 11.8 billion years ago requires matching those ancient signatures to the oldest surviving globular clusters, which continue to orbit the Milky Way as remnants of that first major intake. The survival of these cluster populations provides a tangible link to the galaxy’s primordial composition, allowing researchers to map the chemical evolution of the earliest epoch directly rather than inferring it from simulations alone. With LKH now confirmed as the earliest merger associated with our galaxy, astronomers can anchor their models of galactic formation to a concrete timeline, ensuring that the narrative of Milky Way assembly begins with an active period of accretion shortly after the Big Bang instead of a gradual buildup during later eras.
The resolution of this mystery demonstrates how much of a galaxy’s earliest history remains hidden even when modern instruments scan the present-day universe for clues. The LKH evidence closes a gap between observation and theory, providing physical confirmation that dwarf galaxy interactions were part of the initial accretion framework rather than secondary disruptions to an already mature structure. Astronomers can now reference a definitive merger within the Milky Way’s opening chapters, using the recovered globular clusters to test predictions about how quickly and violently galaxies grew during the most turbulent periods of cosmic history.