Orbital evolution of binary systems

Valli, Ruggero (2026): Orbital evolution of binary systems: the effect of supernova kicks and the interaction with circumbinary disks. Dissertation, LMU München: Faculty of Physics

Abstract

The evolution of massive stars is often shaped by interactions with a companion. The two stars can gravitationally perturb each other, exchange mass, and even merge. The size and eccentricity of the orbit both determine what kind of interactions can happen, and are shaped by them, preserving a memory of the past interactions. Understanding how the orbit evolves during key evolutionary phases of a binary can thus provide insightful clues about the mechanisms that govern binary evolution. In this thesis, I first address the question of what is the result of the interplay between a binary and a surrounding gaseous disk. I develop a new framework for predicting the evolution of such systems, discuss equilibrium configurations and the long-term outcomes. Then, I investigate the death of massive stars, showing how the present-day orbit of binary systems can be used to infer the birth properties of the neutron stars they contain, and the properties of their progenitor stars. I discover two new modes of neutron star formation, corresponding to two different populations of progenitors that differ in pre-explosion mass and neutron star birth velocity. The existence of these populations was previously not recognized, and understanding their origin is a novel theoretical challenge, which I address in the last part of the thesis. There, I suggest an evolutionary explanation for the mass dichotomy of the two populations, based on their mass transfer history, and demonstrate its viability using detailed binary evolution simulations. The orbital properties of binary systems thus emerge as a powerful window into physical processes that are otherwise difficult to observe directly, from the dynamics of circumbinary disks to the mechanism of core-collapse supernovae. The same physical processes leave traces in many different kinds of systems, and future progress will come from combining constraints across them, using the full diversity of binary populations as complementary windows onto the same underlying physics.

• Item Type: Theses (Dissertation, LMU Munich)
• Subjects: 500 Natural sciences and mathematics; 500 Natural sciences and mathematics > 530 Physics
• Faculties: Faculty of Physics
• Language: English
• Date of oral examination: 13. July 2026
• 1. Referee: Mink, Selma de
• Signature of the printed copy: 0001/UMC 32096