The Milky Way, our home galaxy, is a product of continuous collisions and mergers with other galaxies throughout the Universe. Recent research has shed light on a significant aspect of the Milky Way’s history, indicating that its last major merger occurred much more recently than previously believed. The European Space Agency’s Gaia mission, launched in 2013, has played a crucial role in unveiling the secrets of our galactic past.

Gaia’s meticulous mapping of 1 billion astronomical objects, predominantly stars, has allowed scientists to observe the aftermath of galactic collisions. These collisions leave behind distinct patterns, referred to as “wrinkles”, within the Milky Way’s structure. By analyzing the precise positions and velocities of stars, Gaia can detect these wrinkles and trace the timeline of the Milky Way’s last major merger.

Contrary to common assumptions, the Milky Way becomes less “wrinkly” over time, providing a unique insight into its evolution. The discovery of an Fe/H-rich region within our galaxy, known as ‘the Splash’, further supports the theory of a recent major merger. Stars within the Splash exhibit eccentric orbits and share a common chemical fingerprint, indicative of a shared origin due to the merger’s influence.

Two competing scenarios, Gaia Sausage/Enceladus (GSE) and Virgo Radial Merger (VRM), offer explanations for the Milky Way’s unique structures and stellar compositions. Recent data from Gaia has bolstered the case for the VRM hypothesis, suggesting that the wrinkles observed in the Milky Way resulted from a collision less than 3 billion years ago. The complexity of the Milky Way’s merger history poses challenges in distinguishing between stars originating from different merger events.

By running simulations based on observed data, researchers can recreate the merger events that shaped the Milky Way. These simulations offer valuable insights into the timeline and effects of galactic mergers. The latest findings propose that a dwarf galaxy collided with the Milky Way approximately 2.7 billion years ago, marking the occurrence of the Virgo Radial Merger.

As Gaia continues to provide new data and enhance our understanding of the Milky Way’s history, astronomers are continually revising their knowledge of the galaxy’s formation and evolution. The intricate web of mergers and collisions that have shaped the Milky Way underscores the dynamic nature of galaxies and the constant evolution of our cosmic surroundings.

The ongoing research into the Milky Way’s merger history serves as a testament to humanity’s quest for unraveling the mysteries of the cosmos. With each new discovery, our understanding of galactic dynamics and formation processes deepens, paving the way for further revelations about the origin and evolution of galaxies. Gaia’s contributions to this field of study highlight the importance of space exploration in expanding our knowledge of the universe and our place within it.


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