CAREER: Mixing and Oscillations in Novae

White dwarfs are the dense remnants of stars like our sun after their nuclear fuel runs out. Often, they are found in binary systems (two stars orbiting each other). In such systems, the two stars can exchange matter as they age and change size. When white dwarfs gain material from a companion, they undergo explosions on their surfaces, known as novae, losing some or all of the gained matter to space. If such a white dwarf can grow in mass appreciably over many novae, it can be totally destroyed in a massive explosion known as a type Ia supernova. Type Ia supernovae produce roughly half of the iron in the universe and are used as distance measures in cosmology, but we do not fully understand what causes them. In this project, the investigator and a team of undergraduate researchers will use the Modules for Experiments in Stellar Astrophysics (MESA) software tool to study mass-gaining white dwarfs. They will clarify how nova explosions affect the long-term evolution of white dwarf masses. Additionally, they will investigate how X-ray emission from a nova may be used to measure the mass of the underlying white dwarf. Freely available educational activities utilizing MESA for use in undergraduate astrophysics courses will be developed. This program will probe the effects of diffusion, rotation, and convective boundary mixing on the mass retention efficiency of novae. The group will investigate each mechanism individually before combining two and all three at a time. Since these mixing mechanisms can cause core material to be ejected in the nova event, they may lead to a net mass loss over a single nova cycle. This study will constrain what circumstances, if any, allow a white dwarf to grow to the Chandrasekhar mass from hydrogen accretion alone, shedding light on the Type Ia supernova progenitor problem. To aid in measuring white dwarf masses, the group and collaborators will analyse the MESA models with the open-source GYRE stellar oscillation software to determine if the dominant core oscillation modes in nova models match the observed oscillations in the post-outburst X-ray emission of novae. If such a link can be established, it would provide a robust measure of white dwarf mass and perhaps composition. The investigator will develop online materials to train other researchers on using MESA. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.