Astronomers propose that the Milky Way galaxy's stellar disc tilted by more than 90 degrees [1] following a collision with a dwarf galaxy.
This discovery provides a critical window into the turbulent formation of the galaxy. Understanding these early movements helps researchers explain the current orientation of the Milky Way and the environment that existed before the Solar System formed.
The event involved a violent encounter with a dwarf galaxy known as the Gaia Sausage [1]. According to the research team, this collision occurred approximately 10 billion years ago [2]. The impact was severe enough to reorient the entire stellar disc, effectively flipping the galaxy's alignment in a process of cosmic gymnastics [2].
Such a dramatic shift suggests that the early Milky Way was far more volatile than previously understood. The interaction with the Gaia Sausage dwarf galaxy did not just add new stars to the system, it fundamentally altered the structural geometry of the galaxy's disc [4]. This reorientation happened long before the sun and its orbiting planets took shape, meaning the galaxy's current layout is the result of a cataclysmic prehistoric event.
Researchers used data from the study of ancient mergers to reconstruct the path of the Gaia Sausage. The evidence indicates that the collision forced the stellar disc to rotate significantly [4]. By analyzing the motion of stars and the remnants of the merged galaxy, the team determined the scale of the tilt [1].
The findings rewrite the known history of the galaxy's evolution. The scale of the rotation — exceeding 90 degrees [1] — points to a level of instability that is rare in mature spiral galaxies. This suggests that the growth of the Milky Way was driven by violent acquisitions rather than steady accumulation.
“The Milky Way's stellar disc tilted by more than 90 degrees”
This research indicates that the Milky Way's current structure is not a result of gradual evolution, but rather the outcome of a violent, transformative event. By identifying the Gaia Sausage collision as the catalyst for a 90-degree shift, astronomers can better model how galactic mergers influence the distribution of matter and the eventual stability of planetary systems.
