WoU-MMA: Toward an Understanding of Common Envelope Interactions of Binary Stars

Harvard University, Cambridge MA

Investigators

Abstract

Changes in observational astronomy are revolutionizing the way we understand the transient night sky. Major efforts in optical surveys and the detection of gravitational waves from merging binaries of compact objects have revealed a dynamic, time-varying universe. A research team at Harvard University will develop computational models to study how common envelope binary-star interactions lead to astronomical transients in the process of the assembly of compact, merging binaries, which will eventually produce gravitational waves. During the common envelope phase, one star in a pair of stars grows to engulf its companion. Drag forces cause the two stellar cores to spiral closer together in the midst of these gaseous surroundings. Binaries that emerge from this interaction exhibit tightened orbits and transformed properties. The details of the common envelope phase, however, remain uncertain. This work will advance computational modeling tools to allow direct model-to-data comparison for astronomical transients generated by mass ejection during common envelope interactions. The project includes an effort to bring stellar astrophysics to a broader community through an informal-education outreach program called "AstroBike." This work pursues the brief but violent common envelope phase of binary star interaction in which one star evolves to engulf its binary companion. During the ensuing hydrodynamic interaction, the binary is transformed by the processes of orbital tightening and mass accretion. The common envelope process is far from rare -- about 10% of stars are in binary systems that will interact. Furthermore, common envelope phases are believed to be critical in the formation of tight binaries of black holes and neutron stars that can merge under the influence of gravitational radiation, the source population for gravitational wave and multi-messenger astrophysics. The work will make direct comparisons of computational models of common envelope interactions with systems detected as astronomical transients through the generation of synthetic observables. This work addresses the Interpretation criterion of NSF's "Windows on the Universe: Multi-Messenger Astrophysics" program by building models that will maximize the interpretive value of multi-messenger observations in revealing the evolutionary processes that lead to the merging-binary source population. 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.