Hubble data reveal one of the Milky Way's earliest mergers

Astronomers using the Hubble Space Telescope have identified one of the Milky Way's earliest known galactic mergers, a collision with a dwarf galaxy that occurred roughly 11.8 billion years ago, just 2 billion years after the Big Bang Source: elnacionalve. The findings, published in Nature Astronomy and led by Davide Massari of the Observatory of Astrophysics and Space Science in Bologna, shed new light on the galaxy's formative years Source: infobae.

The discovery

The team analyzed 39 globular clusters—dense stellar groups that act as cosmic archaeological sites—using Hubble observations and advanced statistical models to determine their ages and chemical compositions Source: diariolibree. They identified a distinct population of clusters that originated in a dwarf galaxy they named LKH ('Low-energy-Kraken-Heracles') Source: elnacionalve. This galaxy, with a stellar mass similar to that of Gaia-Sausage-Enceladus, merged with the young Milky Way and deposited most of its material in the galaxy's inner regions Source: infobae.

Context and significance

The Milky Way grew by absorbing smaller galaxies, a process known as galactic cannibalism Source: abces. The most recent major merger, with the Sagittarius dwarf galaxy, began over 6 billion years ago and continues today Source: diariolibree. The newly identified merger predates the well-known Gaia-Sausage-Enceladus collision, which occurred about 10 billion years ago Source: elnacionalve. While sources agree on the existence of this early merger, they differ on its exact timing: some report 11.8 billion years ago Source: infobae, while others suggest 12.3 billion years ago Source: abces. This discrepancy highlights the ongoing debate about the galaxy's early history.

Key points

• The merger involved a dwarf galaxy named LKH, identified through globular cluster analysis Source: elnacionalve.
• The event occurred roughly 11.8–12.3 billion years ago, depending on the source Source: infobae, abces.
• The findings provide a clearer timeline of the Milky Way's initial growth Source: diariolibree.