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Supermassive Stars May Have Been Born Amid Globular Clusters

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Astronomers propose a new theory that attempts to explain the existence of peculiar chemical elements in ancient clusters of stars called globular clusters.

What Are Globular Clusters?

Globular clusters are ancient compact clusters of hundreds of thousands stars clumped tightly together via gravity. These clusters formed 11 to 13 billion years ago, just a few cosmic moments after the Big Bang. Around 150 of these clusters have been spotted sitting at the outer regions of the Milky Way.

For decades, scientists studying the beginnings of the Universe have been flummoxed by a long-standing mystery around globular clusters. They wanted to know why the stars found in these clusters have different chemical elements than other stars found in open clusters.

Aside from the significantly higher amounts of helium and hydrogen, stars in globular clusters also have heavier concentration of heavy elements than other stars such as the Sun. This is often seen in older stars such as those found in globular clusters, but scientists have yet to know what caused this particular ratio of elements.

The elements and their particular ratio could not have been produced within the stars themselves. Scientists believe it requires a temperature 10 times hotter than that of the stars while they were forming.

A team of astronomers at the University of Surrey in England believe they may have found the answer to this decades-old question. The answer, they say, could be seen in supermassive stars.

Supermassive Stars At The Borders Of Globular Clusters

In a paper published in the Monthly Notices of the Royal Astronomical Society, the researchers advance the idea that supermassive stars may have come around at the same time as the globular clusters were starting to form. Supermassive stars have a mass that is tens of thousands of times more than the mass of the Sun.

During the early years of the Universe, globular clusters were filled with dense hot gas that would later cool to form the cluster's huge number of stars. As the stars accumulated more material, the researchers believe they became so big and so close to one another that some of them would collide to form a supermassive star.

The supermassive star would then reach temperatures high enough to be able to produce the heavy elements and other chemicals that can now be observed in stars in globular clusters. The fast winds gushing amid the stars would have carried these elements from the supermassive star and deposited them in the other stars in the particular ratio they can be measured in today.

"What is truly novel in our model is that the formation of the supermassive stars and the globular clusters are intimately linked," says lead investigator Mark Gieles, "and this new mechanism is the first model that can form enough material to pollute the cluster, and with the correct abundances of different elements."

Gieles and his team plan to test their idea by using powerful telescopes that can look into the inner regions of globular clusters.

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