Supermassive Star May Have Shaped Chemistry of Milky Way Clusters

(CN) — A supermassive star thousands of times larger than the sun may have been what caused Milky Way stars in globular clusters to have such unique chemistry, new research shows.

Scientists at the University of Surrey in England say in a study published Thursday in the journal Monthly Notices of the Royal Astronomical Society that the supermassive star was big enough and close enough to the other stars in the Milky Way to “pollute” them with the chemistry that makes them so different from other stars in the galaxy.

There are over 150 old globular clusters in the Milky Way. Gravity holds together these dense globular clusters, which contain hundreds of thousands of stars that are almost as old as the universe itself, according to the study.

But something has puzzled scientists for the last 50 years: why these globular clusters have different chemistry than the other stars in the Milky Way.

Scientists had thought that this different chemical makeup could not have been produced in the stars, since the temperatures required to form them are about 10 times higher than the temperatures of the stars themselves.

Now scientists at the University of Surrey assert that a supermassive star formed at the same time as the globular clusters, and the temperature of the supermassive star was hot enough to form the chemical elements absent from other stars. This supermassive star was able to “pollute” the other stars in the cluster with the different chemical makeup, the study says.

Professor Mark Gieles of the University of Surrey, lead author of the study, said the discovery was made through a modeling process.

“What is truly novel in our model is that the formation of the supermassive stars and the globular clusters are intimately linked,” he said. “This new mechanism is the first model that can form enough material to pollute the cluster, and with the correct abundances of different elements, which has been a long-standing challenge.”

The team of scientists says it now proposes to test their new model of globular clusters and supermassive star formation with existing and yet-to-be created telescopes that can peer deep into the regions where the globular clusters formed — looking back into the galaxy when the universe was very young.

“There have been many attempts to solve this problem that has puzzled astronomers for decades,” said professor Henny Lamers of the University of Amsterdam, a co-author of the study. “I believe that this is the most promising explanation that has been proposed so far.”

Lamers said he was “especially proud” that the study was the result of a collaboration between a group of his colleagues and former students who are experts in different branches of astronomy.

Globular clusters were thought to have formed during the earliest days of the universe nearly 14 billion years ago. The clusters contain some of the oldest stars in the Milky Way.

The clusters, however, may not be as old as previously thought. New research at the University of Warwick shows that globular clusters may be 4 billion years younger than previously surmised.

Their research was published last month in Monthly Notices of the Royal Astronomical Society.  

In order to gauge the age of globular cluster stars, scientists compare the physical properties of the light received from globular clusters against properties of starlight that other stars produce.

The new study from the University of Warwick took a different approach. Scientists there used models called binary population and spectral synthesis models. They hypothesized that binary stars, with the help of gravity, steal light from a nearby star, therefore making the emitting star look older than it is.

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