A galactic fossil reveals a secret merger in our home galaxy
In short: The Milky Way is a beautiful spiral, but its shape hides a violent history of collisions. By studying a massive stellar system tucked inside our galaxy's bulge, astronomers have uncovered evidence of a prehistoric merger that occurred nearly 12 billion years ago.
Galactic archeology allows scientists to reconstruct the evolution of our home galaxy by examining the debris left behind by ancient events. While the Milky Way is approximately 13.6 billion years old, its current structure is the result of multiple mergers. Previous research identified two major collisions: one that is still ongoing and another that occurred roughly 10 billion years ago. However, new evidence suggests a third significant merger happened even earlier.
The key to this discovery lies in Terzan 5, a massive stellar system located within the Milky Way's central bulge. For a long time, it was classified as a globular cluster—a group of stars typically containing only one ancient population. However, data from NASA’s James Webb and Hubble Space Telescopes revealed that Terzan 5 is actually a self-contained, self-enriching system with up to four distinct star populations.
Due to its significant size, Terzan 5 preserved its distinct character despite merging with lesser systems within the bulge eons ago; it resembles a 'lump in an otherwise well-mixed cake batter.' Scientists discovered that one specific cluster originated roughly 12 billion years ago by examining these isolated populations. This timing aligns with the era when the Milky Way itself was still assembling, providing a clear fossil record of a merger that shaped our galactic neighborhood.
These findings are significant because they challenge our understanding of how galaxies grow. By peering through dense dust using Webb's infrared capabilities, astronomers can catalog fainter stars to map out these complex histories. Terzan 5 serves as a unique laboratory for understanding the mechanics of galaxy formation and the preservation of ancient stellar records in crowded regions.
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Sources
- Summary by Intellect · source: A 12 billion year old fossil found inside the Milky Way
- Also: NASA Webb, Hubble Reveal History of Relic of Milky Way’s Formation - NASA Science
- Also: phys.org — 12 billion years old, this interstellar comet is older than our solar system
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