Using clustering of star clusters to measure underlying gas and dust distributions in galaxies
From spiral to dwarf galaxies alike, newborn star clusters appear to arrange themselves according to the same underlying physics. Drew Lapeer, a second-year PhD student at the University of Massachusetts Amherst, has recently published a first-author paper on using star clustering to trace the underlying distribution of gas associated with emerging young star clusters.
Most stars are not born alone, they are born in close knit families composed of the same collapsing gas and dust. When looking at galaxies outside of the Milky Way and our closest neighbors, individual stars become nearly impossible to resolve optically; stellar clusters remain a reliable tracer of recent star formation. The caveat to observing these young star clusters is that they are often embedded in the very material from which they formed. Because these clusters are still emerging from their birth clouds, we refer to them as emerging young star clusters (eYSC). That is what makes them useful. As Lapeer explains, “Because eYSCs are so spatially linked to the distribution of this gas and dust, we can use them as tracers of that structure”. Our best chance of peering through the gas and dust in which these eYSCs are embedded is through infrared observations with the James Webb Space Telescope. With these capabilities, the focus of Lapeer's work becomes: if we map where these newborn clusters appear, can we uncover the hidden patterns that govern how stars form across entire galaxies?
To do this, Lapeer takes a slight deviation from the classical measurements of brightness and color. Instead, they examine how star clusters are arranged relative to one another using a statistical tool called the two-point correlation function. They describe it with a dartboard analogy: if darts land randomly, occasional groupings happen by chance. But if clusters appear together more often than randomness predicts, something must be influencing where they land. In galaxies, that “something” is the structure of the gas and dust where stars form.
To test this idea, Lapeer required a diverse selection of galaxies from which to sample stellar clusters. The data came from the FEAST program, which aims to study stellar feedback across a wide range of star-forming environments. Three out of the four galaxies sampled in this sample are grand-design spiral galaxies, but even these differ dramatically – from spirals with central bars or interacting companions to dwarf galaxies experiencing starbursts. Each of these environments has distinct gas distributions, dynamics, and structural features. If the clustering is consistent across these galaxies despite these differences, it strengthens the argument for a common underlying physical mechanism.
What makes this work especially compelling is that it did not begin as some grand effort to uncover a universal picture of star formation. Rather, it emerged almost serendipitously – Lapeer was looking over some older papers using the exact same statistical methods and thought to apply this method to new JWST data. As Lapeer puts it, “I tend to work a little fast and loose – I try things and see if there’s a thread worth pulling.” This time, there was.
When Lapeer applied the two-point correlation function to embedded clusters across the sample of galaxies, a clear pattern became clear. Despite differences in dynamics, morphology, and star formation history,, the clustering followed remarkably similar trends. The signal neither dissolved into randomness nor varied significantly between systems. Instead, it pointed at something deeper: evidence that star formation is governed by a universal physical process. For Lapeer, this was the moment when the statistics became tangible, providing direct evidence for a very long standing theory of some universal physical process.
Lapeer, who led the study as first author, followed a nontraditional path into astronomy. Growing up in rural Michigan, they began their academic journey at Macomb Community College before transferring to the University of Michigan, where they double-majored in astrophysics and interdisciplinary physics. Their research now focuses on the baryon cycle — the complex interplay between star formation, stellar feedback, and galactic gas.
Beyond the scientific results, this project marked an important milestone for Lapeer. It was their first first-author paper, a goal they set even before starting graduate school. Achieving that in their first year was, as they describe it, “personally the most gratifying”. Their role extended far beyond running analysis. Lapeer coordinated feedback from multiple co-authors, responded to referee reports, and navigated the delicate balance of deciding which suggestions strengthened the paper and which required further discussion. “Going through comments and deciding what to keep, that was the hardest part,” they admit. “Do I agree with this? Should I talk to this person more? It can be daunting.”
At the same time, that challenge is what made the experience so rewarding. They emphasized that, while they benefited from strong guidance from advisors and collaborators, they ultimately took the lead and are proud of the work they accomplished. They also noted that the project was carried out entirely through their own analysis and writing, without the use of generative AI. Professionally, what stands out most is that the project transformed abstract statistical methods into a concrete physical insight. “We were able to pull real, tangible results from something that feels esoteric,” they say. “That was incredibly rewarding.”
This project also opens numerous avenues for future work. Lapeer notes that the two-point correlation function is one of many statistical tools that can be used to study spatial structure. Other methods offer complimentary ways to quantify clustering, each building on the same core question: how exactly does structure in gas translate into structure in stars?
When asked what they would tell their younger self, or an incoming undergraduate, Lapeer offered advice that reaches far beyond mathematics and statistics. They speak openly about coming from a nontraditional background without what they describe as “cultural capital,” the know-how to traverse the landscape of academia. To help others navigate a similar path, they have even written a guide explaining how to apply to graduate school and what makes a strong application. More broadly, they encourage students to hold on to what got them into the field. “Astronomy is probably the closest thing we have to pure art in science,” they reflect. “It’s about learning about the universe simply to learn about the universe.” In the midst of deadlines, referee reports, and long coding sessions, that sense of wonder can be easy to lose. Lapeer emphasizes the importance of maintaining balance and well-being while pursuing science, driven both by the desire to uncover the universal processes that shape the cosmos and by a more personal motivation to understand our origins and help others explore that journey.
About the author: Dan Kidwell is a senior undergraduate studying astronomy and physics at UMass Amherst. He currently works in high-energy astronomy, conducting simulated observations of stellar winds in the Galactic Center. Outside of his studies, he enjoys hiking, camping, and photographing the night sky.