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Astronomers are Watching a Newly Forming Super Star Cluster
Six or seven billion years ago, most stars formed in super star clusters. That type of star formation has largely died out now. Astronomers know of two of these SSCs in the modern Milky Way and one in the Large Magellanic Cloud (LMC), and all three of them are millions of years old.
New JWST observations have found another SSC forming in the LMC, and it’s only 100,000 years old. What can astronomers learn from it?
SSCs are responsible for a lot of star formation, but billions of years have passed since their heyday. Finding a young one in a galaxy so close to us is a boon for astronomers. It gives them an opportunity to wind back the clock and see how SSCs are born.
New research published in The Astrophysical Journal presents the new findings. It’s titled “JWST Mid-infrared Spectroscopy Resolves Gas, Dust, and Ice in Young Stellar Objects in the Large Magellanic Cloud.” The lead author is Omnarayani (Isha) Nayak from the Space Telescope Science Institute and NASA’s Goddard Space Flight Center.
At about 160,000 light-years away, the LMC is close in terms of galactic neighbours. It’s also face-on from our vantage point, making it easier to study. The N79 region in the LMC is a massive star-forming nebula about 1600 light-years across. The JWST used its Mid-Infrared Instrument (MIRI) and found 97 new young stellar objects (YSOs) in N79, where the newly discovered super star cluster, H72.97-69.39, is located.
This image from the NASA/ESA/CSA James Webb Space Telescope shows N79, a region of interstellar atomic hydrogen that is ionized and is captured here by Webb’s Mid-InfraRed Instrument (MIRI). N79 is a massive star-forming complex spanning roughly 1630 light-years in the generally unexplored southwest region of the LMC. At the longer wavelengths of light captured by MIRI, Webb’s view of N79 showcases the region’s glowing gas and dust. Star-forming regions such as this are of interest to astronomers because their chemical composition is similar to that of the gigantic star-forming regions observed when the Universe was only a few billion years old, and star formation was at its peak. Image Credit: ESA/Webb, NASA & CSA, M. Meixner CC BY 4.0 INT
Stellar metallicity increases over time as generations of stars are born and die. The LMC’s metallic abundance is only half that of our Solar System, meaning the conditions in the new SSC are similar to when stars formed billions of years ago in the early Universe. This is another of those situations in astronomy where studying a particular object or region is akin to looking into the past.
“Studying YSOs in the LMC gives astronomers a front-row seat to witness the birth of stars in a nearby galaxy. For the first time, we can observe individual low-mass protostars similar to the Sun forming in small clusters—outside of our own Milky Way Galaxy,” said Isha Nayak, lead author of this research. “We can see with unprecedented detail extragalactic star formation in an environment similar to how some of the first stars formed in the universe.”
The YSOs near the SSC H72.97-69.39 (hereafter referred to as H72) are segregated by mass. The most massive YSOs are concentrated near H72, while the less massive are on the outskirts of N79. The JWST revealed that what astronomers used to think were single massive young stars are actually clusters of YSOs. These observations confirm for the first time that what appear to be individual YSOs are often small clusters of protostars.
A composite image created using JWST NIRCam and ALMA data. Light from stars is shown in yellow, while blue and purple represent the dust and gas fueling star formation. Image Credit: NSF/AUI/NSF NRAO/S.Dagnello
This finding brings attention to the complex processes of early star formation. “The formation of massive stars plays a vital role in influencing the chemistry and structure of the interstellar medium (ISM),” the authors write in their published research. “Star formation takes place in clusters, with massive stars dominating the luminosity.”
One of the five young stars is over 500,000 times more luminous than the Sun. As revealed by the JWST Near InfraRed Camera (NIRCam), it’s surrounded by more than 1,550 young stars.
This Spitzer image from the new research shows the N79 region in the LMC. N79 consists of three giant molecular clouds. Spitzer data showed that each of the red circles is a massive young stellar object of at least eight solar masses. However, the JWST has revealed that three of them, with the exception of the one in N79W, aren’t individual YSOs; they’re clusters. Together, they could make up a very young super star cluster. Image Credit: Nayak et al. 2025.
Previous Atacama Large Millimeter/submillimeter Array (ALMA) observations hinted at what might contribute to the formation of SSCs. ALMA showed that colliding filaments of molecular gas at least one parsec long are in the region. These filaments could be behind H72’s formation.
This figure from previous research shows ALMA observations of the region near the super star cluster H72. Each one shows carbon monoxide in a different velocity channel. The white “x” shows the location of H72. “Scrolling through the channels it is clear there is a filament in the northeast to southwest direction and a distinct filament in the northwest to southeast direction,” the authors explain. Image Credit: Nayak et al. 2019.
This work highlights JWST’s power to resolve complex star formation locations in other galaxies. Not only did the JWST show us that what appeared to be individual YSOs are actually groups of stars, but it allowed the researchers to determine their mass accretion rates and chemical properties. The JWST’s new data gives astronomers new insights into complex chemistry, including the presence of organic molecules, dust, and ice in star-forming regions.
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