Astronomers Revise Timeline of Milky Way's Last Major Merger

New data from the European Space Agency's Gaia mission suggests the Milky Way's last major galactic collision happened less than three billion years ago, far more recently than the previously accepted estimate of eight to eleven billion years.

Astronomers reached the conclusion by mapping ripples, or wrinkles, in the orbits of more than 100,000 stars, features that form as stars swing back and forth through the galaxy's center.

Researcher Thomas Donlon explained that studying how these wrinkles fade over time reveals when the galaxy last experienced a big crash.

Heidi Jo Newberg of Rensselaer Polytechnic Institute noted that if the stars had arrived eight billion years ago, overlapping wrinkles would have blurred together and become indistinguishable.

The team argues the ripples came not from the ancient Gaia Sausage Enceladus merger but from a more recent event they call the Virgo Radial Merger, which pulled in a family of smaller dwarf galaxies and star clusters.

Published in Monthly Notices of the Royal Astronomical Society, the finding could rewrite the timeline of how our galaxy assembled its present shape.