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Milky Way merger 11.8 billion years ago identified in star clusters
Researchers used Hubble and Gaia to study stellar clusters in the inner 20,000 light-years and estimate the dwarf galaxy contained stars totaling about 500 million solar masses at the time.
A study cited by Reuters says astronomers have found evidence that the Milky Way absorbed a smaller dwarf galaxy roughly 11.8 billion years ago, when the universe was less than 15 percent of its current age.
Scientists examined stellar clusters near the Milky Way’s center, using the orbiting Hubble and Gaia telescopes to measure their ages, chemical makeup and trajectories across the galaxy’s innermost 20,000 light-years.
The researchers estimate the absorbed dwarf galaxy, named Low-energy-Kraken-Heracles or LKH, included stars with a total mass equivalent to about 500 million times the sun at the time of the merger, roughly a quarter of the Milky Way’s stellar mass then.
According to the study, the event represents the Milky Way’s earliest-known galactic merger and helped supply stars and interstellar gas that could feed later star formation, along with dark matter.