Illuminating Star Birth: JWST Reveals the Life Stages of Emerging Star Clusters in M83

Star formation doesn’t happen one star at a time. Instead, most stars form in groups called clusters, born from the collapse of large gas clouds. Some of these clusters are gravitationally bound and can live for millions or even billions of years, while others disperse quickly into the galaxy. Understanding the earliest stages of these clusters—when they are still surrounded by gas and dust—has been difficult because visible light can’t penetrate these thick birth clouds. In this study, Alice Knutas and her collaborators use the James Webb Space Telescope (JWST) to peer through the dust and examine the early lives of star clusters in the nearby spiral galaxy M83.

Observations: Peering into M83 with JWST

The team observed M83, a galaxy about 4.7 million parsecs (roughly 15 million light-years) away, which is known for its high rate of star formation. Using JWST’s Near Infrared Camera (NIRCam), they collected images across several infrared wavelengths, allowing them to detect both the glowing gas surrounding young stars and a type of warm dust emission. They combined this data with older images from the Hubble Space Telescope to get a complete picture of clusters at all stages of development.

Identifying Emerging Star Clusters

Knutas et al. define three types of emerging young star clusters (eYSCs) based on the features they emit. The most embedded clusters, eYSCI, show both strong hydrogen line emission and the 3.3 µm PAH feature. Slightly older clusters, eYSCII, show hydrogen emission but no detectable PAH feature. A third group consists of sources that show only the PAH signal, and their nature is still unclear—they might be young clusters without massive stars, or they could be older remnants. This classification helps the authors trace how clusters gradually shed their birth clouds and become visible in optical light.

Analyzing Cluster Properties

The researchers use a computer modeling tool called CIGALE to estimate the age, mass, and dust content of each cluster by comparing their light across many wavelengths. They find that eYSCI are the youngest and most dust-enshrouded, while optical clusters (oYSCs), which can be seen in visible light, are older and less obscured. Most clusters become fully exposed within about 6 million years, but more massive clusters clear their surroundings faster, sometimes in just 5 million years. Interestingly, only about 20–30% of the eYSCs are likely to become long-lasting, gravitationally bound clusters.

Environmental Effects: The Role of Galactic Structure

The study shows that the environment within M83 has a major impact on star cluster formation. The most massive clusters form in the central starburst region, where gas is funneled by the galaxy’s bar structure. In contrast, the outer regions form fewer and smaller clusters. By dividing the galaxy into zones (like the bar, spiral arms, and outer disk), the authors reveal how different parts of the galaxy influence the mass and age of star clusters. These results support earlier studies suggesting that bars and central regions in spiral galaxies can create more extreme star-forming conditions.

The Emergence Sequence: Tracing Cluster Evolution

Color-color diagrams—graphs comparing brightness in different infrared wavelengths—help illustrate the life stages of eYSCs. The authors show a clear progression: clusters start as eYSCI with both dust and gas signatures, then evolve into eYSCII as they lose their dust, and finally become visible as oYSCs. The transition appears to happen over a few million years. A small number of very deeply embedded clusters may exist, but they seem to represent only a short-lived phase. This result helps refine our understanding of how quickly stars can clear out the gas and dust around them.

Conclusion: A New View on Star Cluster Formation

This work demonstrates the power of JWST to uncover the youngest, most hidden stages of star cluster formation. By studying eYSCs in M83, Knutas and colleagues provide new insights into how long clusters remain embedded, how their mass affects their emergence, and how their galactic environment influences their development. These results will help astronomers better understand how galaxies turn gas into stars—and how many of those stars remain together in long-lived clusters. Future studies across other galaxies in the FEAST program will expand on these findings and test how universal these processes really are.

Source: Knutas