Our Milky Way galaxy contains some 150 billion-year-old globular clusters, each with approximately one million stars, orbiting the thin stellar halo of our galaxy. Image Credit: Denis Belitsky via Shutterstock / HDR tune by Universal-Sci

An international team of astronomers has uncovered the remains of an ancient collection of stars pulled apart by the Milky Way more than two billion years ago. The archaeological find of the fragmented globular cluster is unusual because the stars contain much less heavy elements than other globular clusters. The result suggests that the original structure of the collection of stars was very different from that of today's star clusters.

The research, led by PhD student Zhen Wan from the University of Sydney, Australia, also included the Groningen astronomer Eduardo Balbinot, who discovered the so-called Phoenix-stream four years ago. The results will be published in the science journal Nature tomorrow.

Our Milky Way contains some 150 billion-year-old globular clusters, each with approximately one million stars, orbiting the thin stellar halo of our galaxy.

Out of the mentioned 150 globular clusters the gorgeous Messier 80  stellar swarm is perhaps one of the most well known globular clusters - Image Credit: NASA, The Hubble Heritage Team, STScI, AURA via Wikimedia Commons — Out of the mentioned 150 globular clusters the gorgeous Messier 80 stellar swarm is perhaps one of the most well known globular clusters - Image Credit: NASA, The Hubble Heritage Team, STScI, AURA via Wikimedia Commons

For their research, the scientists used the Anglo-Australian Telescope in New South Wales, Australia. It measured the velocities of star flow in the southern constellation Phoenix. One of the discoveries made revealed that the stars are the remains of a globular cluster that was pulled apart by the Milky Way's gravity about two billion years ago.

In a Nova press release, first author Wan stated that, although the globular cluster was destroyed billions of years ago, he and his team can deduce from the composition of the stars that it originated in the early universe.

Until now, astronomers have assumed that stars in star clusters always have a certain percentage of heavier elements formed in earlier generations of stars. But that hypothesis does not hold for the star cluster in the Phoenix Current. The levels of heavy elements are actually far below the minimum level that is actually necessary to even form a cluster.

A possible explanation is that the Phoenix Current is the last of its kind, the remnant of a population of globular clusters that was born in completely different circumstances from today's star clusters.

Groningen astronomer and co-author Eduardo Balbinot stated that when he discovered the Phoenix current in the data from the Dark Energy Survey (DES), it was already a mysterious object. He is, therefore, delighted that there has been follow-up research that solved some of the mystery. However, there is still a lot of theoretical work to do because the research has also raised numerous new questions.

Currently, the scientists are looking for other ancient remains of this extraordinary category of globular clusters.

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