2026 Theses Doctoral

Shock and Awe: Probing the Galactic Mass Reservoir with NuSTAR Measurements of White Dwarf Masses and Searches for Dark Matter with GAPS

Bridges, Gabriel L.

"What we don't know could fill a book", and indeed, this thesis concerns two profound unknowns in modern astrophysics. Cosmological and astrophysical observations indicate that nearly eighty-five percent of all matter in the universe is "dark matter", a substance whose composition is entirely unknown. Similarly, more than ninety-five percent of all stars will end their lives as white dwarfs, yet the formation and evolution of these stellar remnants, especially in binary systems, is ill understood.

The nature of dark matter is one of the greatest mysteries of modern physics. Despite the overwhelming evidence for its existence and dominance in the cosmic matter budget, no known particle has the necessary properties to explain it. Identifying dark matter would therefore open a window onto physics beyond the Standard Model. Low-energy cosmic-ray antinuclei are especially powerful probes of dark matter because their astrophysical production is kinematically suppressed. In particular, low-energy antideuterons have virtually no astrophysical background but are readily produced in many dark matter models, including those inaccessible to current terrestrial experiments. The General Antiparticle Spectrometer (GAPS) is the first experiment optimized for the detection of low-energy antideuterons. I led the integration, testing, launch, and flight of the first GAPS scientific payload and will play a central role in the analysis of data from this groundbreaking flight.

A second astrophysical mystery concerns the evolutionary history of white-dwarf binary systems, particularly the origin of their magnetic fields. Several plausible models exist, but observational evidence is sparse, in part because measuring white dwarf masses in contact binary systems is challenging. To address this problem, I have developed a model of accretion in these systems that enables robust mass measurement from X-ray spectroscopy alone.

Together, these two lines of inquiry use astrophysical systems as laboratories for fundamental physics. In this thesis, I search for rare antimatter signatures of dark matter with GAPS and develop new tools to characterize compact stellar remnants in interacting binaries. These efforts advance our ability to probe phenomena that cannot be fully understood through terrestrial experiments alone.