Challenging the Standard Paradigm of TŻO Formation

In this talk, I will present a start-to-end simulation that examines the long-term fate of high-mass X-ray binary LMC X-4, as a means to understand how Thorne-Żytkow objects may be produced. A Thorne-Żytkow object (TŻO) is a conjectured type of star wherein a red giant or red supergiant contains a neutron star at its core, claimed to possibly be formed by the engulfment of a neutron star by an evolving giant star companion. LMC X-4 is modeled using a 3D hydrodynamical simulation after the primary fills its Roche lobe and engulfs the neutron star companion. Our findings suggest that the canonical framework of TŻO formation via common envelope needs to be modified, as the post-merger accretion feedback will unbind the vast majority of the surrounding envelope after the neutron star merges with the core. Additionally, I will discuss the prospects of a bright transient with a luminosity and duration typical of an ultra-long gamma-ray burst, triggered by the neutron star core collapsing into a black hole.