When Evan Kirby, associate professor in the Department of Physics and Astronomy at the University of Notre Dame, listed a job posting with “galactic archeology” in the title, he didn’t expect to hire Roman Gerasimov.
Kirby’s research focuses on measuring the composition and abundance of stars. He needed a postdoctoral fellow to write software analysis code for measuring molecules in stellar atmospheres. Gerasimov, who previously studied at the University of California San Diego, wrote his doctoral thesis on modeling the spectra of brown dwarfs — which aren’t exactly star material. These substellar bodies are much cooler than stars, meaning their atmospheres hold greater volumes of hard-to-measure molecules. Kirby realized if Gerasimov could make models of brown dwarf spectra, he could handle stars.
Kirby invited Gerasimov to interview on campus. Gerasimov came prepared with several spectra he’d made to show Kirby. This extra effort cinched Kirby’s hunch: Gerasimov was a brilliant candidate, one he’d be lucky to hire. In September 2023, Gerasimov joined his lab as a University of Notre Dame Society of Science Fellow, and the two began working together on the Subaru Prime Focus Spectrograph (PFS) Project.
“The project is absolutely giant,” shared Gerasimov. Led by the National Astronomical Observatory of Japan, it enlists more than 12 institutions from seven different countries to build a new spectrometer for installation on the Subaru Telescope in Maunakea, Hawaii. The instrument contains 2,400 optical fibers that can target stars and other objects to render spectra for data analysis. Researchers hope to target 100,000 stars over the course of a survey.
“We’re looking at older stars — both in our galaxy and a few adjacent galaxies,” explained Gerasimov. “These stars preserve the fossilized footprint of the chemistry of the universe when those stars first formed.” As a result, he and Kirby can see “how the evolution of our galaxy and a few adjacent galaxies progressed.” For example, ordinary stellar explosions give rise to basic elements like carbon and oxygen. More energetic events correspond to exotic and complex elements like Europium. These elements illuminate the origins of the Universe and its evolution, including that of human life.
The project’s massive scale has resulted in breakthroughs for science and technology alike.
It requires levels of precision that necessitate custom-built solutions, such as the piezoelectric motors attached to each fiber that ensure micron-level accuracy. When the project needed calibration lamps, astronomer James Gunn of Princeton University found a neon lamp artist in Arizona who designed a bespoke parabolic reflector. The lamp provided uniform illumination across an extremely confined space. This innovative solution was also cost-effective — an important consideration for projects like PFS, which require careful budgeting despite $100 million in funding.
Kirby is a leader in the PFS project, but he stressed the value of Gerasimov’s contributions. “It’s no exaggeration to say he’s been transformative to my research group,” said Kirby. “Roman is in a different class because he’s a peer … I learn as much from him as he learns from me.” Example lessons include computational techniques for building more efficient models and insights into stellar physics. Their strongest shared common interest is globular clusters, which Gerasimov’s thesis focused on.
Indeed, Gerasimov wanted to continue his research adjacent to his work with Kirby. So he responded to an open call from the PFS project for ancillary science programs. Because the spectrograph doesn’t simultaneously utilize all 2,400 fibers, researchers can find other uses for those spare fibers — say, for observing brown dwarfs. The project accepted Gerasimov’s case. Additionally, Notre Dame provides him further support and funding for his research interests.
The project will begin surveying in February 2025. It has allowed Kirby and Gerasimov to share insights and expertise with researchers from vastly different fields. It will likely open doors for Gerasimov further down the road, but where it shines the brightest is its potential legacy. The technological achievements can benefit the world of optics at large through commercial and defense applications. Multiple generations of future astronomers will likely devote their careers to the project, and then there’s the legacy of the stars themselves, which will spin long after the telescope shuts down.
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Story by Elisia Guereña