Populations of mass-transferring binary stars

A key challenge in binary star astrophysics, including research on the origins and evolution of gravitational wave progenitors, is reconciling the evolutionary expansion of stars (up to several AU) with the tight separations found in compact-object binaries like those containing white dwarfs, neutron stars, and black holes (often less than 0.1 AU). Mass transfer between binary components plays a critical role here, significantly affecting both orbital separation and the physical properties of the stars.

One possible result of mass transfer is a contact binary, where the two stars orbit so closely that they share a common envelope. Understanding the structure and evolution of these envelopes has been an open question since the 1960s. The prevailing theory suggests that these binaries exchange mass at a high rate over timescales of hundreds of thousands of years. Recent interest focuses on massive contact binaries, which may represent an evolutionary stage on the path to gravitational wave mergers. However, progress in this field has long been stalled by limited access to consistent data and gaps in theoretical models.

In this project, we aim to analyze large, uniform populations of contact binaries to better understand how different astrophysical processes shape their structure and evolution. We will utilize newly available light curve data (from TESS and Kepler), physical parameters (from Gaia and extensive spectroscopic surveys), and previous work by our group applying machine learning to classify binary types (Pešta & Pejcha 2023, 2024). The project may also involve modeling with stellar evolution codes.

References:

[1] Pešta & Pejcha, 2023, Mass-ratio distribution of contact binary stars, https://ui.adsabs.harvard.edu/abs/2023A%26A...672A.176P/abstract
[2] Pešta & Pejcha, 2024, Distinguishing between light curves of ellipsoidal variables with massive dark companions, contact binaries, and semidetached binaries using principal component analysis, https://ui.adsabs.harvard.edu/abs/2024arXiv240811100P/abstract