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UMD Astronomers Help Discover a First for the Early Universe

Birth of Star Clusters in Nascent Galaxy Helped Transform the Cosmos

By Emily C. Nunez

star clusters

Using the James Webb Space Telescope, an international team of astronomers including UMD researchers discovered five young massive star clusters in the Cosmic Gems arc, a galaxy 13 billion light years away.

Images courtesy of ESA/Webb, NASA & CSA, L. Bradley (STScI), A. Adamo (Stockholm University) and the Cosmic Spring collaboration

Using NASA’s James Webb Space Telescope, an international team of scientists including two University of Maryland astronomers revealed the birth of five massive star clusters in the Cosmic Gems arc, a galaxy that formed less than 500 million years after the Big Bang.

The findings, published this week in the journal Nature, mark the first discovery of so-called compact star clusters—extremely dense groups of stars bound by gravity—in an infant galaxy.

Though the light from this galaxy has been traveling for nearly 13 billion years across vast distances to reach Earth, the Webb telescope was able to see the Cosmic Gems arc in high resolution due to a phenomenon known as gravitational lensing. When gravity bends light, it can “act as a telescope, magnifying anything behind it,” and the galaxy just happens to be situated behind one of these natural lenses, explained study co-author and UMD astronomy Professor Massimo Ricotti.

annotated star clusters: lensed galaxy redshift (z): 2.6. lensed galaxy redshift (z): 10.2. mirrored star clusters redshift (z): 10.2.foreground galaxy cluster redshift (z): 0.97
A field of many galaxies is pictured on the right, while the left panel shows two distinct galaxies, including the Cosmic Gems arc.

“These star clusters are among the farthest objects that we have ­­­discovered with Webb, so it’s an incredible magnification,” Ricotti said. “We were able to see compact star clusters that are one parsec in size, which is very small on a cosmological scale. For comparison, the distance between our sun and the center of our galaxy is about 8,000 parsecs.”

Hubble was the first space telescope to observe this distant galaxy, but Webb’s near-infrared camera enabled astronomers to study its millions of densely packed stars in minute detail.

“The surprise and astonishment was incredible when we opened the Webb images for the first time,” said the study’s lead author, Angela Adamo of Stockholm University and the Oskar Klein Centre in Sweden. “We saw a little chain of bright dots, mirrored from one side to the other—these cosmic gems are star clusters! Without Webb we would not have known we were looking at star clusters in such a young galaxy.”

The research team determined that the formation of these star clusters likely played a role in shaping the properties of galaxies during the universe’s early history. Young galaxies underwent bursts of star formation that generated substantial amounts of radiation, changing the chemical composition of the cosmos and enabling light to travel more freely in a process known as reionization.

Some astronomers—including Ricotti—have argued that these early compact star clusters could have evolved into the globular star clusters that we see today, which are similarly dense. Ricotti said his theory was previously considered unpopular, but thanks to Webb, new observations are helping to fill gaps in the universe’s history.

The research team plans to collect more data on the Cosmic Gems arc in hopes of understanding the physical properties of its star clusters in greater detail. And in the future, the team hopes to build a sample of galaxies for which similar resolutions can be achieved.

“I am confident there are other systems like this waiting to be uncovered in the early universe, enabling us to further our understanding of early galaxies,” said study co-author Eros Vanzella from the INAF - Astrophysics and Space Science Observatory of Bologna.

This article was based in part on a press release from the European Space Agency.



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