Interacting white dwarfs in binaries and triples

Rajamuthukumar, Abinaya Swaruba (2025): Interacting white dwarfs in binaries and triples. Dissertation, LMU München: Fakultät für Physik

Abstract

White dwarfs are the most common endpoints of stellar evolution and play a crucial role in various astrophysical phenomena, such as thermonuclear explosions, compact binary mergers, and gravitational wave sources. While the evolution of white dwarfs in binary systems has been extensively studied, many open questions remain, particularly regarding the interactions that lead to thermonuclear events such as Type Ia supernovae. Moreover, the role of hierarchical triples in shaping white dwarf formation and interactions is less well understood. In this thesis, I investigate how both binary and triple-star dynamics shape the white dwarf population and influence their interactions. First, I conduct a population synthesis study of hierarchical triples using the Multiple Stellar Evolution MSE code, focusing on the impact of stellar evolution, binary interactions, and dynamical effects on white dwarf formation. This study simultaneously considers both the single and double degenerate channels and accounts for triples across the entire parameter space, including those with tight inner binaries. Additionally, I investigate the effects of typically overlooked or uncertain physics, such as fly-bys and common envelope prescription parameters. By comparing the outcomes of triple and binary evolution channels, I assess the significance of triples in producing Type Ia supernovae. Next, I use the MESA stellar evolution code to model He star + white dwarf systems in detail. These simulations represent the most up-to-date study of single degenerate progenitors, exploring an extensive grid of hot subdwarf + white dwarf configurations and their possible evolutionary outcomes, including double white dwarf formation, helium novae, and thermonuclear explosions. Additionally, I calculate the runaway velocities of surviving donor stars in systems where an explosion occurs. Finally, I examine the contribution of white dwarfs from the triple channel to the Galactic population of double white dwarfs detectable by the Laser Interferometer Space Antenna (LISA). By combining MSE with a Milky Way-like galaxy model from cosmological simulations TNG50, I construct a synthetic Galactic white dwarf population and compare the contribution from triple systems to that of isolated binaries. While previous studies have primarily focused on binary formation and evolution in isolation, this work presents the first detailed investigation into the role of triple stellar evolution in shaping the LISA double white dwarf population. I predict both the total number of double white dwarfs from the triple channel contributing to LISA's astrophysical noise and the number of individually resolvable double white dwarfs. This thesis emphasizes the critical role of binary and hierarchical triple systems in the formation and evolution of white dwarfs, as well as their influence on shaping the observable population of compact objects. The findings have significant implications for gravitational wave astronomy, interacting white dwarf binaries, progenitors of Type Ia supernovae, and our broader understanding of binary and multiple-star evolution.

• Dokumententyp: Dissertationen (Dissertation, LMU München)
• Themengebiete: 500 Naturwissenschaften und Mathematik ; 500 Naturwissenschaften und Mathematik > 530 Physik
• Fakultäten: Fakultät für Physik
• Sprache der Hochschulschrift: Englisch
• Datum der mündlichen Prüfung: 8. Mai 2025
• 1. Bericht­erstatter:in: Mink, Selma de