THE Milky Way cannibalised a galaxy one quarter of its mass 10 billion years ago, according to new research.

Smaller galaxies merge to create bigger ones, and form and evolve hierarchically.

Published in Nature Astronomy, the research provides an accurate dating of Milky Way stars, scientists say.

While the chemical make-up of the Milky Way’s stars point to a significant merger in its past, when this happened remains under debate.

Carme Gallart, from the Instituto de Astrofisica de Canarias in Spain, and colleagues have built what they say is an accurate

image of the age distribution of stars in the current disk and inner halo of the Milky Way. They found the majority of stars in the halo of the Milky Way closer to the sun have ages ranging up to 10bn years old.

Using simulations, the authors identified this as the point when the precursor of the Milky Way merged with one of its then companions, Gaia-Enceladus.

The authors say accurate distances to individual Milky Way stars now provided by the Gaia spacecraft mission have allowed them to derive the ages, adding: “Because accurate stellar ages were lacking, the time of the merger and its role in our galaxy’s early evolution remained unclear.

“Here we show that the stars in both halo sequences share identical age distributions, and are older than most of the thick-disk stars. The sharp halo age distribution cut-off at 10bn years ago can be identified with the time of accretion of Gaia-Enceladus to the Milky Way.”