The Milky Way’s formative years
Nature Astronomy
July 23, 2019

The Milky Way cannibalized a galaxy one-quarter of its mass ten billion years ago, according to a paper published online this week in Nature Astronomy. The research provides an accurate dating of Milky Way stars.
Galaxies form and evolve hierarchically, with smaller galaxies merging to form bigger ones. The chemical makeup and kinematics of the Milky Way’s stars point to a significant merger in the galaxy’s past, but when this event happened remains under debate.
Carme Gallart and colleagues built an accurate image of the age distribution of stars in the current disk and inner halo of the Milky Way. They find that the majority of stars in the halo of the Milky Way closer to the Sun have ages ranging up to ten billion years old. With the help of cosmological simulations, the authors identified this age limit as the point when the progenitor of the Milky Way merged with one of its then companions, named Gaia - Enceladus.
Knowing the exact ages of stars has also enabled the authors to pinpoint the stars that were present before the merger and those that originated in the assimilated galaxy. Stars that appear redder, due to their higher metal content, trace the original stars formed in the Galaxy pre-merger. The merger not only heated (or puffed up) some of the stars formed in the Galactic disk to be part of its halo but also provided the Milky Way with material to create new stars and give it its current appearance.
doi: 10.1038/s41550-019-0829-5
Research highlights
-
Jan 15
Environment: Seagrass meadows may facilitate marine plastic removal from the seaScientific Reports
-
Jan 15
Planetary Science: Mercury may have shrunk less than previously thoughtCommunications Earth&Environment
-
Jan 13
Environment: Polyester fibres found to be widespread in the ArcticNature Communications
-
Dec 23
Planetary science: Over 100,000 new craters identified on the MoonNature Communications
-
Dec 22
Conservation: Agricultural expansion could cause widespread biodiversity declines by 2050Nature Sustainability
-
Dec 18
Geology: Alpine summits may have been ice-free during life of Tyrolean IcemanScientific Reports