New Webb Telescope Discovery: ‘Superstars’ Created The Weird Globular Clusters In Our Galaxy

It’s almost globular cluster season. One of the mysteries of our galaxy and every other, these dense groupings of up to a million stars—the most massive and oldest star clusters in the Universe—are a beautiful sight in a small telescope

As seen from the Orion spiral arm where we are these ancient relics appear clustered around the center of our galaxy, which in summer becomes visible to those of us in the northern hemisphere.

But whether you get eyes-on with the Great Globular in Hercules, the Sagittarius Star Cluster, Omega Centauri or any of the other 177 visible around the halo of our Milky Way, known that some elusive questions about globular clusters remain unanswered by astronomers. What are they, where did they come from, and—perhaps most intriguing—why are the millions of stars in any one of these dense clusters radically different in composition? After all, they must have been born in the same dust cloud.

Answers have eluded astronomers for centuries, but new images by the James Webb Space Telescope (JWST) suggest an answer to all those questions—globular clusters could be caused by supermassive stars.

Published today in Astronomy and Astrophysics, the researchers claim to have found the first chemical trace of supermassive stars in globular proto-clusters existing about 440 million years after the Big Bang.

The supermassive stars in question are extraordinarily large—they’re about 5,000 to 10,000 times more massive and five times hotter at their center than the Sun.

Finding traces of such stars is complicated by the fact that supermassive stars burn fast and die young. Unlike globular clusters.

‘‘Globular clusters are between 10 and 13 billion years old, whereas the maximum lifespan of superstars is two million years,” said Mark Gieles, ICREA professor at the University of Barcelona and co-author of the study. “They therefore disappeared very early from the clusters that are currently observable. Only indirect traces remain.”

Cue JWST’s images of one of the most distant and youngest galaxies known to date in our Universe, GN-z11 (first identified in 2016 by Hubble and the Keck Observatory), which is but a few tens of millions of years old. Its light shows that very high levels of nitrogen, which, say the authors, can only be explained by the combustion of hydrogen at extremely high temperatures. GN-Z11 also contains a very high density of stars. This all suggests that globular clusters are forming inside while a supermassive star still exists, claim the authors.

It’s a tantalizing clue as to the origin of these clumps of ancient stars. The authors will continue to use JWST to study globular clusters in distant galaxies to confirm their theory.

Wishing you clear skies and wide eyes.