Common Envelope Evolution and the Origins of Massive Compact Binaries

University Of Illinois At Urbana-Champaign, Urbana IL

Investigators

Abstract

Close binary systems experience a brief period in which both stars become embedded in a common gaseous envelope - the Common Envelope (CE) phase. Before its ejection, drag forces within the envelope shrink the stars' separation, leaving behind a much closer system. If both stars are massive (8-100 solar masses), exotic binary systems comprised of neutron stars and black holes may result, which are of great interest as being the likely progenitors of gamma-ray bursts, kilonovae, and gravity wave sources. However, current simulations of the CE phase are unable to achieve envelope ejection for many systems in which it should occur, with the added problem of insufficient orbital shrinkage or "inspiraling." This discrepancy has been attributed to missing physics or insufficient spatial resolution/duration in the simulations. The principal investigator (PI) and team will use 3D radiation-hydrodynamical simulations to address several important questions regarding CE evolution in massive, close binary star systems by considering for the first time the energy released by H/He recombination in the envelope as well as stellar winds and pulsations. The questions to be addressed include (1) the possible roles these mechanisms play in envelope ejection, (2) what kinds of systems result, and (3) whether there are observational signatures that will allow these events to be recognized. This award will also support research efforts of one graduate and two undergraduate students each year, an extension of the Illinois Astrophysical Dynamics Demos site, plus participation in a summer astronomy camp. The PI's team will use radiation-hydrodynamic simulations to study the evolution of common envelope (CE) binaries comprised of a red supergiant and a neutron star or black hole companion. This configuration plays a key role in formation scenarios for high-mass X-ray binaries, binary black holes, and binary neutron stars. To achieve envelope ejection and inspiraling in these systems they will use adaptive mesh refinement simulations that include both H and He partial ionization and radiation diffusion in a self-consistent manner. By including time-dependent envelope heating, the researchers will also explore the role of dynamical pulsations in assisting envelope ejection. And by directly monitoring the emergent radiative flux they will also generate light curves to determine which observational signatures might be useful as triggers for follow-up time-domain survey observations. The results of these simulations will directly guide the work of the binary population synthesis community, whose predictions for the number of gravitational wave sources, double degenerate Type Ia supernovae, and X-ray binaries are sensitive to this evolutionary phase. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.