Exploring the Life and Legacy of Stars: Melissa Rasmussen

When PhD student Melissa Rasmussen describes her research, she doesn't shy away from the cosmic scale of the questions she asks.

"One of the big applications for what I do is the question of where all the elements in the universe come from," she said. "We know that heavier elements, like iron, form from supernovae, or stars blowing up. But the details of how, and in what amounts, depend on the physics we put into our models. That's what we're trying to figure out."

Rasmussen, now in her third year of the physics PhD program at Stony Brook University, is part of a research community working at the intersection of nuclear astrophysics and computational science. Her day-to-day work may involve sifting through massive code bases, tinkering with simulation parameters, or running computational models that can take months to complete. But the motivation is timeless: understanding how the building blocks of Earth, and life itself, were forged in the hearts of stars.

From Utah to Stony Brook

Rasmussen's path to Stony Brook began in Utah, where she studied physics as an undergraduate at Utah State University. During her junior year, she participated in a Research Experience for Undergraduates (REU) program with Michael Zingale, professor in the Department of Physics and Astronomy at Stony Brook. "At the time it was fully remote. But even so, I loved it," Rasmussen recalled. "The science problem we worked on was fascinating, and I really felt like Professor Zingale valued my curiosity and the questions I asked." That summer experience left such an impression that when it came time to apply to graduate programs, Stony Brook was at the top of her list.

Her choice proved prescient. At Stony Brook, Rasmussen found not only a mentor whose style matched her own but also an institutional environment rich in resources for computational research. She points to the Institute for Advanced Computational Science (IACS) as a particularly supportive hub, where physicists, mathematicians, and computer scientists collaborate on large-scale simulation challenges. "I've been able to take classes outside the physics department - in computer science, applied math, and numerical methods - that really broaden my perspective," she said. "It's exciting to see how techniques developed in one field can transform another."

Zingale notes that Rasmussen's contributions already extend well beyond her individual project. "Melissa is collaborating on a suite of codes that our entire group uses," he said. "Her contributions will benefit all of the projects in the group, just as contributions from others benefit hers. An important part of our codes is that they are all open source, freely available online."

Simulating Exploding Stars

At the core of Rasmussen's dissertation work is the daunting task of modeling the collapse and explosion of massive stars. This is not a problem that yields easily to pencil-and-paper calculations. Instead, it depends on exascale computing resources and advanced methods like adaptive mesh refinement, which allows simulations to zoom in on regions of interest, such as the turbulent zones where nuclear burning occurs, while using coarser grids elsewhere.

Interestingly, the same computational methods that Rasmussen employs to study stellar explosions have applications far beyond astrophysics. Adaptive mesh refinement is also used in weather modeling and even in epidemiology, where researchers tracked the spread of COVID-19 using similar grid-based approaches. "It's amazing that the same mathematical principles can be applied to storms on Earth, to pandemics, and to stars exploding across the galaxy," she said. "That's one of the things I love about computational science: it can be so collaborative."

Her simulations are also pushing against the limits of dimensionality. While many groups rely on 1D or 2D models, Rasmussen is exploring 3D approaches that more accurately capture turbulence and mixing effects. "If you model turbulence in 2D, it behaves in the opposite way from what we know it does in 3D," she explained. "That means some long-standing approximations are probably misleading. Ultimately, I'd love to see a complete 3D model of a massive star's death, from collapse to explosion to dispersal into space. That would be a real scientific legacy."

Zingale adds that Rasmussen's interests reflect the strength of Stony Brook's research ecosystem. "Melissa's core interests are in computational science," he said. "The work we do uses techniques like designing and developing simulation codes, leveraging supercomputers, and analyzing simulations to answer questions in astrophysics. But these same core techniques carry to other fields as well, which is why computational science is so exciting. It opens doors far beyond any one discipline."

The Value of Curiosity

For Rasmussen, part of the challenge and the thrill of research lies in navigating uncertainty. When new experimental data on nuclear reaction rates becomes available, she and her collaborators incorporate it into their models to see how predictions shift. "It can take a lot of time just to figure out where in the code you need to make a change," she said with a laugh. "But every time you work through that puzzle, you come away with a deeper understanding."

She's quick to admit that her work does not have immediate, practical applications. "Honestly, we study this because it's really cool," she said. "It's a privilege of living in a society where so many people are doing the hard, necessary work that keeps things running. Our work is about satisfying humanity's desire to understand the world." Still, she notes that astrophysics has historically driven technological progress, particularly in supercomputing and data analysis, which often spill over into other domains.

Looking to the future, Rasmussen hopes to apply her computational expertise to areas with more direct societal benefit, such as renewable energy. "If I'm going to pivot at some point, that's the direction I'd like to go," she said. "For now, I'm grateful to be learning from these cosmic systems. But eventually, I'd like to bring that experience back to Earth."

Building Community

Rasmussen is funded by the prestigious Department of Energy Computational Science Graduate Fellowship, which fully supports four years of doctoral study related to high-performance computing. Being a fellow provides her with collaboration opportunities with computational scientists across institutions, professional development funding, and the chance to work at national labs around the country, which extends her reach as a scientist during her graduate studies. Importantly, Rasmussen has used the flexibility provided by the fellowship to invest time in improving the student experience at Stony Brook.

"It started with my own struggles," Rasmussen said. "But once we talked to other students, we realized it wasn't just me. Many of us felt unprepared in different ways. Instead of letting that discourage us, we worked with faculty to create a solution. Now, future students will hopefully be better equipped for the coursework and the research to come."

This ethos of community support extends to her peers as well. Rasmussen credits the graduate student cohort at Stony Brook with being a vital source of intellectual and emotional support. "The student community here has been amazing," she said. "It's not just about research collaboration. It's about helping each other through the ups and downs of graduate school."

A Vision for the Future

As Rasmussen reflects on her journey so far, she's mindful of both the immediate challenges and the larger arc of her career. In the short term, she hopes to contribute to the growing body of 3D stellar models, helping to bridge the gaps between different research groups and simulation approaches. Longer term, she sees herself pivoting toward problems like sustainable energy, where computational modeling can directly improve lives.

Her broader hope, though, is that her work inspires others to stay curious. "We don't always know what discoveries will matter most," she said. "But the act of pursuing them, of asking questions and building tools to answer them, always moves us forward."

In the end, Rasmussen's story is one of expansive curiosity, grounded both in the mysteries of the cosmos and in the lived experience of her peers. Whether modeling the turbulent death of stars or helping new graduate students find their footing, she embodies the spirit of a scientist committed not only to discovery but also to community.