PhD Defense by Sophie Lund Schrøder

Drag in binaries

Compact binaries allow us to study many spectacular and fantastic astrophysical phenomena. The evolution of massive stars in binaries is filled with interesting, open questions that we are just now beginning to be able to answer. The aim of this thesis has been to investigate the evolution of compact binary stars to gravitational wave sources via hydrodynamical simulations of interacting stellar binaries. The thesis is organised in three main parts. In part I, we present models for merger-driven explosions that arise after the merger between a star and compact object following a common envelope event. In the merger accretion onto the compact object produces a neutrino-cooled a disk, and the envelope material is expelled into the surrounding environment, forming a dense circum stellar medium. This event is accompanied by the release of approximately 1051 erg into the surrounding medium, leading to an explosion with a light curve shaped by the merger-produced circum stellar medium.

In part II, we explored the effect on LIGO sources of forming the second compact object in a fallback supernova. We found that the observed black hole systems with smallerMand positive χeff could be formed in fallback supernova. And we propose that GW200115,a black hole neutron star system, was formed in a fallback supernova. Its neutron star has a mass is more massive than mean observed for Galactic binary neutrons stars, and its black hole has a mass close to the lower side of the black hole mass distribution, both of which are possible to form in fallback supernova of a helium star of 10.0 M only depending on the supernova energy. Finally, in part III we investigate the characteristics of an electromagnetic counterpart to a binary black hole merger after a fallback supernova. In a fallback supernova, the ejecta material settles in mini disks around each black hole and accretion continues. We predict that the accretion luminosity at time of merger is ≈ 1035 erg/s for systems formed in symmetric explosions, and can be an order of magnitude higher for systems formed in asymmetric supernova with kicks.