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Astronomers say odd globular cluster is a fossil remnant of the early Milky Way

"Terzan 5 could represent an intriguing link between the local and the distant universe, a surviving witness of the galactic bulge assembly process," said astronomer Francesco Ferraro.

By
Brooks Hays
Astronomers say Terzan 5 is like no other globular cluster they've observed. Photo by ESO/VLT
Astronomers say Terzan 5 is like no other globular cluster they've observed. Photo by ESO/VLT

BOLOGNA, Italy, Sept. 7 (UPI) -- Astronomers believe a unique cluster of stars known as Terzan 5 is a Milky Way building block frozen in time. The fossilized relic is offering scientists insights into how the Milky Way first formed.

Astronomers have known about Terzan 5 for some time, but until recently they didn't have the full picture. New observations have rendered the cluster -- positioned 19 000 light-years away in the constellation of Sagittarius -- in unprecedented detail. The new data confirms the cluster's originality.

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As revealed by data collected using the European Southern Observatory's Very Large Telescope, Terzan 5 features two unique sets of stars, each comprising distinct ages and chemical compositions.

The evidence suggests the globular cluster hosted two periods of stellar activity, the second divided from the first by approximately 7 billion years.

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The most sophisticated models of galactic formation suggest the Milky Way was formed by the slow but steady amalgamation of small halo-like collections of stars and gas. These mini-halos merged over time, with older stars becoming concentrated within the Milk Way's central bulge and later additions -- featured younger stars -- aligning themselves around the outside.

Terzan's stellar contents resemble those found within the Milky Way's central disc, suggesting it may be one of the galaxy's earliest buildings blocks -- a block that failed to fully fuse with its peers and instead became fossilized.

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"We think that some remnants of these gaseous clumps could remain relatively undisrupted and keep existing embedded within the galaxy," astronomer Francesco Ferraro from the University of Bologna said in a news release. "Such galactic fossils allow astronomers to reconstruct an important piece of the history of our Milky Way."

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Ferraro is the lead author of a new paper on Terzan 5, published this week in the Astrophysical Journal.

Astronomers hope further study of the globular cluster could offer insights into the nature of galaxy formation.

"Terzan 5 could represent an intriguing link between the local and the distant universe, a surviving witness of the galactic bulge assembly process," concluded Ferraro.

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