Physics Colloquium – Sarah Villanova Borges

Constraining Common Envelope Evolution Simulations with Observations

Sarah Villanova Borges, PhD Candidate
University of Wisconsin-Milwaukee

Common Envelope Evolution (CEE) remains one of the biggest unresolved problems in binary stellar evolution, despite being the primary pathway for the formation of close binary systems. One of the main challenges in understanding CEE is its intrinsically multiscale and multiphysics nature, which makes it difficult to model with analytical or 1D models. 3D hydrodynamical simulations have therefore become essential tools for studying this phase. However, validating these simulations requires observational constraints, which are scarce. This lack of direct observations is another major obstacle in modeling CEE. One exception is luminous red novae, which is believed to correspond to CEE events that culminate in stellar mergers. In contrast, there are no confirmed direct detections of ongoing CEE events that result in the survival of a close binary. As a result, studies must rely on observations of post-CEE systems, such as close binaries, planetary nebulae (PNe) and water fountains (WFs), to constrain both numerical simulations and analytical models. Close binaries primarily provide constraints on the final orbital separation between the stellar core and its companion, while PNe and WFs offer insight into the morphology of the ejected envelope.

During my PhD, I focused on constraining CEE hydrodynamical simulations using observations of those post-CEE systems (close binaries, WFs, and PNe). In this colloquium, I will discuss the key insights I have got into the understanding of CEE during my PhD years.