NASA's Hubble Captures Unusual Mix of Stars Believed to Be Rare Fossil Relic of Ancient Milky Way

An international team of astronomers has discovered that the unusual mix of stars in the stellar cluster known as Terzan 5 could be a rare fossil relic of the early Milky Way.

The discovery, described in a paper published in the Astrophysical Journal, could pave way for a better and more understanding of galaxy assembly, unraveling the mysteries of galaxy formation and complicated history of the Milky Way Galaxy.

"Some characteristics of Terzan 5 resemble those detected in the giant clumps we see in star-forming galaxies at high-redshift, suggesting that similar assembling processes occurred in the local and in the distant Universe at the epoch of galaxy formation," explained lead author Francesco Ferraro from the University of Bologna, Italy, in a statement.

The unusual mix of stars in the Terzan 5, some 19,000 light-years away from Earth, was detected using the data from the Advanced Camera for Surveys and Wide Field Camera 3 on board NASA and ESA's Hubble Space Telescope. There were also data gathered by ground satellites including the Very Large Telescope in Chile.

The astronomers reveal that there are two distinct kinds of stars in Terzan 5 that have an age gap of roughly seven billion years. This suggests that the star formation process in Terzan 5 is not continuous, but was dominated by two distinct outbursts. For the second burst of star formation to be possible, Terzan 5 needs to have large amounts of gas and to be quite massive, about 100 million times the mass of Sun.

Due to its unusual properties, Terzan 5 could be the ideal candidate for a living fossil from the early days of the Milky Way. Furthermore, the astronomers noted that the properties of Terzan 5 have many similarities to the stellar population found in the tightly packed central region of the Milky Way called galactic bulge, making Terzan 5 a fossilized relic of galaxy formation, representing one of the earliest building blocks of the Milky Way.

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