The Milky Way's signature halo is mostly stellar rubble from a cosmic collision 10 billion years ago with another galaxy a quarter of its size, scientists stunned by their own discovery reported Wednesday. The slow-motion crash with Gaia-Enceladus -- named after the giant of Greek mythology born of Earth and Sky -- not only provided the halo's raw material, equivalent to 600 million Suns, it also filled out our galaxy's distinctive disk, they reported in the journal Nature. "We have basically unravelled the formation of the Milky Way," lead author Amina Helmi, an astronomer at the University of Groningen's Kapteyn Astronomical Institute, told AFP.
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