What They Learned: Nick Sweeney ’19

The physics major used his senior thesis to explore methods of conceptualizing dark matter.

Though we can’t see dark matter, a phenomenon described by Nick Sweeney ’19 as “the mysterious material that comprises over 80 percent of matter in the universe,” the astrophysics major found that the subject still encouraged plenty of observations. For his senior thesis, titled “Halo Formation and Ultra-light Axion Dark Matter,” Sweeney analyzed and compared the varying models which are used to conceptualize this invisible substance.

“My thesis enabled me to engage with the competing models for dark matter, and I found this very rewarding,” said Sweeney, who was guided through his research both by his advisor, Assistant Professor of Physics and Astronomy Daniel Grin, and by his experience engaging in similar research in 2018 through the KINSC Summer Scholars program at Haverford.

The amount of time Sweeney dedicated towards his research enabled him to both analyze a series of pre-established models for dark matter and engineer his own code.

“I wrote a computer code in the Python programming language that computes both the ‘clumpiness’ of galaxy clusters during different epochs of the universe, as well as how tightly packed each galaxy is,” said Sweeney.

The senior’s application of his programming to the pre-existing forms of modeling enabled him to achieve a new way of testing the models, a research achievement which helped provide him with the opportunity of presenting at the American Astronomical Society’s meeting at Seattle this past January.

“These opportunities helped me become a better communicator of my work and to share my results with professionals in the field of dark matter, as well as students interested in learning about this field,” he said speaking on the experience.

What did you learn from working on your thesis? 

I learned how applying various different models for dark matter affects the distribution of galaxies in the universe. One particular model posits that theoretical particles, known as axions, are the fundamental constituents of dark matter. This model became the central focus of my inquiry. I enjoyed learning the particle physics background of axions, as well as their hypothesized influence on large-scale structure in the cosmos. In the larger picture, perhaps my biggest takeaway was learning that progress in scientific research is non-linear. There were often weeks when I would make little to no progress, as well as days when I was able to make major breakthroughs on several of the plots central to my thesis.

What are the implications of your thesis research?

My research is impactful because I made both of these kinds of computations for the axion dark matter model. To my knowledge, this model has not been thoroughly tested in this way before. My work is primarily theoretical, but it can also be cross-checked observationally. Thus, my work is potentially helpful to astrophysicists who observationally measure the “clumpiness” of galaxy clusters and their individual densities.

“What They Learned” is a blog series exploring the thesis work of recent graduates.