Astronomers trace Milky Way's oldest known galaxy merger to 11.8 billion years ago
Our galaxy appears to have swallowed a smaller neighbour when the universe was still young, researchers say.
In 30 seconds
Written by the desk, checked before publishResearchers say the Milky Way absorbed a smaller galaxy roughly 11.8 billion years ago. It is the earliest galaxy merger yet identified in our galaxy's history, offering a glimpse of how the Milky Way grew in the young universe.
- The merger is dated to roughly 11.8 billion years ago.
- It is the earliest known galaxy merger in the Milky Way's history.
- The Milky Way absorbed a smaller galaxy in the event.
- Large galaxies are thought to grow mainly by absorbing smaller ones.
What we can confirm
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Claim ledger
Every line traces to a named sourceThe Milky Way absorbed a smaller galaxy about 11.8 billion years ago
- reportedThe Straits Times
- reportedSouth China Morning Post
This is the earliest galactic merger identified so far for the Milky Way
- reportedThe Straits Times
How it unfolded
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The Milky Way absorbs a smaller galaxy
How outlets are framing it
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They say the event marks the earliest merger yet identified in the Milky Way's assembly history.
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First publication.
What happened
Big galaxies like ours do not grow alone. They build up over billions of years by pulling in smaller galaxies, and the stars from those swallowed systems stay behind, still carrying clues about where they came from. Astronomers now say they have identified the oldest such event in the Milky Way's past: the absorption of a smaller galaxy about 11.8 billion years ago, not long after the universe itself began. That makes this the earliest galactic merger known for our galaxy, pushing the record for its assembly history further back in time than previous findings. Work of this kind usually relies on measuring the motions, ages and chemical make-up of stars, since stars from a swallowed galaxy tend to move together and share a distinct composition. The name given to the absorbed galaxy, the size difference between the two systems, and the precise uncertainty on the 11.8 billion year figure have not been detailed publicly.
Why it matters
The Milky Way is the one galaxy we can study star by star, so its history doubles as a test of how galaxies in general form. Pinning down its earliest merger helps set a timeline for when large galaxies started assembling after the Big Bang.
What happens next
Astronomers are likely to look for more stars belonging to the same swallowed galaxy and to check the age estimate with independent measurements. Further surveys of stellar motions and chemistry could reveal whether even older mergers are hidden in the Milky Way.